RU2783122C1 - Composite zoned oxidation catalyst for internal combustion engine with compression ignition - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to a composite zoned oxidation catalyst for use in an exhaust system for exhaust gas purification, an engine containing the specified catalyst, the use of a composite catalyst and a method for its production. The composite catalyst (14, 16, 18, 20) is located in the exhaust system upstream relative to the filter substrate (44, 50) of solid particles, and contains: a substrate (5) having a total length L and a longitudinal axis and having a substrate surface extending axially between the first end (I) of the substrate and the second end (O) of the substrate; and three or more zones (1, 2, 3 or 1, 2, 3, 4) of the catalytic coating of porous oxide arranged in series axially on the surface of the substrate and along it, with the first zone (1) of the catalytic coating of porous oxide having a length of L₁, and L₁ <L, formed at one end by the first end (I) of the substrate, and at the second end by the first end (19, 21) of the second zone (2) of the catalytic coating of porous oxide with a length of L₂, with L₂<L, and the first zone (1) of the catalytic coating of porous oxide contains the first material: a substrate of heat-resistant metal oxide and two or more components deposited on it, representing a platinum group metal containing both platinum and palladium with a mass ratio of platinum and palladium ≥1; the second zone (2) of the catalytic coating of porous oxide contains a second material: a substrate of heat-resistant metal oxide and one or more components deposited on it, representing a platinum group metal, and the third zone (3) of the catalytic coating of porous oxide, containing a third material: a substrate of heat-resistant metal oxide and one or more components deposited on it, representing the platinum group metal is formed at its second end by the second end (O) of the substrate. The total load of platinum group metals in the first zone (1) of the porous oxide catalytic coating is greater than the total load of platinum group metals in the second zone (2) of the porous oxide catalytic coating. The total load of platinum group metals in the third zone (3) of the porous oxide catalytic coating is less than the total load of platinum group metals in the second zone (2) of the porous oxide catalytic coating. The first zone (1) of the catalytic coating of porous oxide contains one or more of the first components, which are alkaline earth metal, deposited on the first material: a substrate of heat-resistant metal oxide.

EFFECT: ensuring a stable exothermic effect at a lower temperature.

19 cl, 11 dwg, 10 tbl, 9 ex

Description

Scope of the invention

The invention relates to a composite zoned oxidation catalyst for use in an exhaust system for purifying exhaust gas produced by an internal combustion engine for a compression ignition vehicle, preferably for a heavy duty diesel vehicle, and located in the exhaust system gases upstream of the particulate filter. The invention further relates to an exhaust system or vehicle containing a composite zoned oxidation catalyst. The invention also relates to the use of a composite zoned oxidation catalyst to generate an exothermic effect for the regeneration of an underlying particulate filter; and a method for producing a composite zoned oxidation catalyst.

Prerequisites for the creation of the invention

Internal combustion engines produce exhaust gases that contain pollutants such as carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO _x ) and particulate matter (PM). Emission standards for pollutants in the exhaust gas emitted by an internal combustion engine, in particular in vehicle engines, are becoming increasingly stringent. There is a need to provide improved catalysts and exhaust systems for treating and removing pollutants in such exhaust gases that can meet these standards and that are cost effective.

Exhaust gas from gasoline and diesel engines is typically treated with a catalyst that can oxidize (i) carbon monoxide (CO) to carbon dioxide (CO ₂ ); and (ii) hydrocarbons (HC) to water (H ₂ O) and carbon dioxide (CO ₂ ). Triple catalysts (TWC) are typically used to treat gasoline engine exhaust gas by reducing oxides of nitrogen (NO _x ) to nitrogen (N ₂ ), water (H ₂ O) and carbon dioxide (CO ₂ ) simultaneously with oxidation reactions ( i) and (ii). Exhaust gas from a compression ignition engine such as a diesel engine is typically treated with an oxidation catalyst (commonly referred to as a diesel oxidation catalyst (DOC)) that performs the oxidation reactions (i) and (ii). Some diesel oxidation catalysts are also capable of oxidizing nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ), which can assist in the removal of NO _x by an additional downstream emission control device.

Oxidation catalysts for compression ignition internal combustion engines typically contain one or more platinum group metals. The selection of the particular platinum group metal(s) to be included in the oxidation catalyst depends on a variety of factors such as reactivity with particular contaminants and under varying exhaust gas conditions, cost, high temperature durability, chemical compatibility with the material. -substrate and any other components of the catalyst and susceptibility to impurity poisoning. For example, both platinum (Pt) and palladium (Pd) are capable of oxidizing carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from a compression ignition engine. Palladium is more susceptible to fuel sulfur poisoning than platinum, but has greater heat resistance.

When the internal combustion engine is a compression ignition engine such as a diesel engine for supplying motive power to a vehicle, the vehicle may be a low power diesel vehicle or a heavy duty diesel vehicle.

The vehicle may be a light duty diesel vehicle (LDV) as defined by US or European law. In the US, a light diesel vehicle (LDV) refers to a diesel vehicle with a gross vehicle weight of ≤8500 lbs (US lbs).

In Europe, a vehicle with a small diesel engine is defined as a vehicle of categories M ₁ , M ₂ , N ₁ and N ₂ with a reference mass ≤2610 kg (EU5/6).

In the United States, a Heavy Duty Diesel Vehicle (HDV), as defined by law, is a vehicle with a Gross Vehicle Weight (GVW) of >8,500 lbs (US lbs) in Federal jurisdiction and over 14,000 lbs in California (1995 model year). a year or later).

In Europe, a heavy duty diesel vehicle is a vehicle designed and constructed for the transport of goods and having a maximum mass (i.e. "maximum technically permitted laden mass") of more than 3.5 tonnes ( i.e. metric tons), but not more than 12 tons (category N ₂ ) or more than 12 tons (category N ₃ ), i.e. cargo vehicles; or a vehicle made and designed for the transport of passengers, containing more than 8 seats in addition to the driver's seat and having a maximum mass or not exceeding 5 tons (category M ₂ ); or exceeding 5 tons (category M ₃ ), i.e. buses and coaches, in accordance with EU legislation (Council Directive 2007/46/EC). In China, the European definition is used in a broad sense.

In Japan, an HDV is a heavy commercial vehicle, defined as a vehicle having a GVW >7500 kg.

In Russia and South Korea, emission standards for high performance vehicles are based on European standards and therefore the above definitions for Europe apply.

In Brazil, an HDV is a vehicle for the transport of passengers and/or goods with a maximum gross vehicle weight of more than 3856 kg or a vehicle platform weight of more than 2720 kg.

In India, HDV is a vehicle with a GVW >3500 kg.

Strategies to meet current emission standards for heavy duty diesel engines typically use an exhaust system architecture containing a number of catalyst substrates and injectors. In order from upstream to downstream (with "upstream" being considered from the engine attached to or capable of being attached to the exhaust system), the exhaust system comprises a hydrocarbon fuel injector, a diesel oxidation catalyst (DOC), a catalyzed particulate filter ( CSF, i.e. catalyzed diesel engine dust filter (DPF)), a urea (ammonia precursor) injector, one or more selective catalytic reduction (SCR) catalysts, and an ammonia slip catalyst (ASC), also known as nitrification (AMOX).

The function of the DOC during normal operation is to control CO and HC emissions, encouraging the conversion of NO to NO ₂ for subsequent passive filter regeneration (burning particulate matter retained on the filter into NO ₂ at lower exhaust gas temperatures than O ₂ in the exhaust gas). gas, ie the so-called CRT ^® effect) as well as acting as a catalyst for the exothermic effect during active CSF regeneration performed by injecting hydrocarbon fuel into the exhaust gas. For the avoidance of doubt, it should be clarified that the fuel injection/exotherm generation event does not occur during normal operation: normal operation is the period between fuel injection/exotherm generation events (see C. Ruehl et al., discussed later in this paper) . CSF controls particulate matter (PM) emissions and stimulates NO → NO ₂ conversion to improve SCR efficiency. Urea, a precursor to ammonia, is injected downstream of the CSF and mixed with the exhaust gas. NO _x conversion is carried out on an SCR catalyst by reaction with ammonia (NH ₃ ) and the unreacted NH ₃ is oxidized on an ammonia slip catalytic catalyst (ASC).

SCR catalysts are configured to selectively catalyze NO _x reduction using a nitrogenous reductant, typically NH ₃ , which can be derived from an ammonia precursor such as urea, the reductant being introduced into the exhaust gas stream upstream of the SCR catalyst in an amount of , sufficient to stimulate the main NO _x reduction reactions:

(1) 4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O;

(2) 4NH ₃ + 2NO ₂ + O ₂ → 3N ₂ + 6H ₂ O; and

(3) NO + NO ₂ + 2NH ₃ → 2N _{2 +} 3/2 H ² O ₍ preferred so-called "fast SCR reaction").

It should be understood that all reactions (1)–(3) can occur in parallel, but the kinetically fastest reaction will be preferable. Thus, in an exhaust gas having a NO ₂ : NO _x ratio of 0.5, the kinetically favorable fast SCR reaction prevails. In most, but not all, applications, some level of exhaust gas recirculation (EGR) is used to reduce the level of NO _x leaving the engine to a level that can then be further reduced by post-treatment with urea and SCR. The DPF is required to reduce the increased PM emissions from the engine due to the use of EGR and to meet the Euro VI particulate limit. When using a high performance SCR, some Euro VI engines may reduce the use of EGR, for example through partial EGR and/or EGR without cooling, or eliminate EGR entirely. As a result, three main strategies have been created to ensure that an engine meets the Euro VI standard:

1. Cooled EGR + SCR.

2. Hot (no cooling) EGR + SCR.

3. SCR only.

Using these strategies, typical high power engine emissions are around 60 ppm. CO and about 10 ppm unburned hydrocarbon fuel. However, all such systems include diesel particulate filters. Particulate filtration systems for diesel engines on a vehicle include the effect of regeneration techniques on the filter media. "Regeneration" is the selected method of burning diesel particulate matter retained on the filter. Regeneration is infrequent, but the period between regeneration events depends on several factors including engine design, filtration efficiency during normal operation, engine load during normal operation, and so on. According to a recent publication, empirical regeneration rates for heavy duty diesel trucks ranged from 3–100 hours and 23–4078 miles (see C. Ruehl et al., Environ. Sci. Technol, 2018, 52(10) , pp. 5868–5874).

Regeneration techniques can be broadly categorized as passive, active, and combinations of passive and active. In passive systems, the particulate oxidation temperature is reduced to a level where the filter can be automatically regenerated during normal vehicle operation. Examples of such passive systems include filter material catalysis; adding a catalytic additive to the fuel, with the possibility of incorporating the soot burning catalyst into the particulate matter on the filter; and generating nitrogen dioxide (NO ₂ ) upstream of the filter to combust particulate matter retained on the filter: the particulate matter burns in NO ₂ at lower temperatures than in oxygen. This is the so-called ^CRT® effect (see, for example, publication EP0341832).

Active systems actively trigger filter regeneration by raising the temperature of the solids trapped in the filter. In practice, this can be achieved in the vehicle by burning the hydrocarbon fuel already present in the vehicle and/or by electrical heating. The two methods of fuel combustion include in-cylinder engine control methods such as late cycle additional fuel injection; or injection and combustion of fuel in the exhaust gas, i. e. after the exit of the exhaust gas from the engine cylinder itself.

In passive-active systems, a "passive" filter catalyst or an upstream (contributing to the ^CRT® effect) NO oxidation catalyst, etc. allows active regeneration to be performed at lower exhaust gas temperatures and/or for shorter periods of time compared to non-catalytic active systems. In either case, the fuel economy disruption associated with active regeneration can be minimized (at the cost of additional catalyst costs). Regeneration at a lower temperature can also reduce thermal stress and increase filter life.

The present invention relates to active regeneration systems or active-passive regeneration systems.

Applicant's publication WO 2013/088152 A1 describes a diesel exhaust gas aftertreatment catalytic system, the system comprising a diesel oxidation catalyst (DOC) and an aftertreatment device located downstream of the DOC, the aftertreatment device requiring periodic heat treatment and means for raising the temperature in the post-treatment device, wherein said DOC contains an upstream zone 0.5 to 2 inches (12.7 to 50.81 mm) long with higher hydrocarbon (HC) oxidative activity than the rest part of the DOC. The description explains that during active filter regeneration, the exothermic effect generated by the contact of the initially "ignited" upstream DOC with the injected hydrocarbon fuel may suddenly be extinguished even while the DOC remains in contact with the injected hydrocarbon fuel.

U.S. Published Application No. US 2014/0271429 A1 describes an oxidation catalyst composite comprising a diesel oxidation catalyst deposited on a substrate in zones, wherein the first porous oxide coating zone adjacent to the inlet end of the substrate has a Pt/Pd ratio of less than 3 : 1 and has a platinum group metal (PGM) load of at least twice that of a second porous oxide coating zone adjacent to the downstream end of the substrate, wherein the first porous oxide coating zone has a length that is less than that of the second zone. porous oxide coatings.

US Published Application No. US 2009/288402 describes a zoned diesel oxidation catalyst having a higher noble metal load in the inlet zone than in the outlet zone, and the inlet zone has the same or shorter length.

EP 2000639 A1 describes a process that claims to extend the range of temperatures at which highly concentrated hydrocarbons can be combusted or at which high temperature gas enters the late stage catalyst more quickly. A method for purifying exhaust gas discharged from an internal combustion engine includes using a catalyst to raise the temperature of the exhaust gas to purify the exhaust gas, and is characterized in that hydrocarbon is introduced in an amount of 1,000 to 40,000 vol. ppm exhaust gas, based on the amount of methane, into the exhaust gas passage of the internal combustion engine upstream of the temperature rise catalyst into the exhaust gas stream. Thus, if a hydrocarbon compound in diesel contains a chain of 16 carbon atoms, as defined in EP '639 A1, that hydrocarbon chain corresponds to 16 times the amount of methane (CH ₄ ).

The catalyst in EP '639 A1 is prepared by supporting a catalytically active component (A) consisting of (a) platinum, (b) an oxide of at least one metal selected from the group consisting of magnesium, an alkaline earth metal and an alkali metal optionally selected from of a group consisting of magnesium, calcium, barium, strontium, and potassium, and (c) at least one element selected from the group consisting of palladium and rhodium, on a refractory inorganic oxide powder substrate (B), and applying the inorganic oxide powder with the catalytically active component held thereon onto a refractory three-dimensional structural base.

The Applicant's publication WO 2015/015182 describes an oxidation catalyst for treating exhaust gas from a diesel engine, the catalyst comprising: a support; a first porous oxide coating region disposed on the substrate, the first porous oxide coating region comprising a first platinum group metal and a first substrate material; a second porous oxide coating region adjacent to the first porous oxide coating region, the second porous oxide coating region comprising a second platinum group metal and a second substrate material; a third porous oxide coating region disposed on the substrate, the third porous oxide coating region comprising a third platinum group metal and a third substrate material; and wherein: (i) the third porous oxide coating region is adjacent to the second porous oxide coating region; or (ii) the second porous oxide coating region is located on or applied to the third porous oxide coating region. The first region of the porous oxide coating may or may not contain an alkaline earth metal.

The Applicant's publication WO 2014/132034 A1 describes an oxidation catalyst for treating exhaust gas produced by an internal combustion engine, the oxidation catalyst comprising a support and a catalyst layer, the catalyst layer comprising: a first support material; the first metal of the platinum group; and a second platinum group metal; wherein the catalyst layer is located on the substrate surface, and the catalyst layer has a non-uniform distribution of the first platinum group metal in a direction perpendicular to the substrate surface. The oxidation catalyst can be used to oxidize carbon monoxide (CO), hydrocarbons (HC) as well as nitrogen oxides (NO _x ) in such an exhaust gas.

WO 2009/076574 describes an emission treatment system and method for eliminating oxides of nitrogen (NO _x ), particulate matter and gaseous hydrocarbons present in diesel engine exhaust streams. The emission treatment system comprises an oxidation catalyst located upstream of the particulate filter located upstream of the NO _x reduction catalyst. The oxidation catalyst contains an inlet zone with an axial length and an outlet zone with an axial length, and the inlet zone contains at least one of platinum and palladium with a first load value, while the outlet zone contains palladium with a second load value, and the outlet zone essentially does not contain platinum, which means that platinum is not intentionally introduced into this zone, but unintentionally, platinum can be less than about 1 wt.% of the metal, with the first load greater than the second load, and the axial length of the inlet zone is less than or equal to the axial length of the outlet zone. The diesel oxidation catalyst comprises a catalyst that is effective in that it does not substantially generate additional NO ₂ to the exhaust gas stream passed through the diesel oxidation catalyst for about 90% of the operating range of the diesel oxidation catalyst.

Applicant's publication WO 2006/056811 describes an apparatus comprising a compression ignition engine and its exhaust system comprising at least one exhaust system component for treating the exhaust gas and means for generating an exothermic effect for heating at least one an exhaust system component, wherein the means for generating an exothermic effect consists essentially of a catalyst and a means for injecting hydrocarbon into the exhaust gas for combustion on the catalyst, wherein the catalyst consists essentially of both a palladium (Pd) component and a platinum (Pt) component , as well as an optional substrate material located on the substrate monolith.

Applicant's publication WO 2014/080200 describes an exhaust system for a compression ignition engine comprising an oxidation catalyst for scavenging carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from a compression ignition engine, the oxidation catalyst comprising : a platinum group metal (PGM) component selected from the group consisting of a platinum component (Pt), a palladium component (Pd), and combinations thereof; an alkaline earth metal component; a substrate material containing a modified alumina comprising a heteroatomic component; and a substrate, wherein a platinum group metal (PGM) component, an alkaline earth metal component, and a substrate material are disposed on the substrate. The examples illustrate tests performed on low power diesel engine exhaust gas compositions using alkaline earth metal loads ≥100 g/ft ³ .

Applicant's publication WO 2014/080202 describes a catalyzed particulate filter for a compression ignition engine comprising an oxidation catalyst for scavenging carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from a compression ignition engine, disposed on a filter substrate, wherein the oxidation catalyst comprises: a platinum group metal (PGM) component selected from the group consisting of a platinum component (Pt), a palladium component (Pd), and combinations thereof; an alkaline earth metal component; a substrate material containing a modified alumina, including a heteroatomic component. Example 8 shows that the oxidation of nitrogen monoxide is dependent on the presence of barium oxide in such catalyst compositions.

WO 2010/118125 describes an oxidation catalyst composite for oxidizing unburned hydrocarbons (HC) and carbon monoxide (CO) and reducing oxides of nitrogen (NO _x ) from a diesel engine, comprising at least two porous oxide coating layers, the first coating being porous oxide contains a palladium component, and while the second coating of the porous oxide contains platinum and at least about 50% of the total platinum, located at the back of the catalyst.

The Applicant's publication WO 2015/110818 A1 describes an oxidation catalyst for treating exhaust gas from a diesel engine and an exhaust system comprising an oxidation catalyst. The oxidation catalyst comprises: a first porous oxide coating region for oxidizing carbon monoxide (CO) and hydrocarbons (HC), the first porous oxide coating region comprising a first platinum group metal (PGM) and a first substrate material; a second porous oxide coating region for oxidizing nitric oxide (NO), the second porous oxide coating region comprising platinum (Pt), manganese (Mn), and a second substrate material; and a substrate having an inlet end and an outlet end; wherein the second porous oxide coating region is preferably arranged to contact the exhaust gas at the outlet end of the substrate and after the exhaust gas contacts the first porous oxide coating region.

The Applicant's publication WO 2017/093720 describes an oxidation catalyst for treating diesel exhaust gas, the oxidation catalyst comprising: a support; a capture material for trapping at least one phosphorus-containing impurity and/or at least one sulfur-containing impurity in the exhaust gas emitted by the diesel engine; and a catalytic region located on the substrate; moreover, the catalytic region contains a catalytic material containing a platinum group metal (PGM) selected from the group consisting of platinum (Pt), palladium (Pd) and a combination of platinum (Pt) and palladium (Pd).

It is believed that there are two main mechanisms for possible poisoning of exhaust gas treatment catalysts from internal combustion engines: (i) selective poisoning, in which the pollutant directly reacts with the active site or catalyst support, resulting in a decrease in activity or a catastrophic loss of activity; and (ii) non-selective poisoning, which results in a loss of efficiency due to steric obstruction of access to active sites or pores in the catalytic support as a result of clogging (or closing) of the surface of the support or active sites. The inventors have found that zinc and (at low temperature) phosphorus (in the form of droplets of phosphoric acid), and droplets of oil themselves (derived from fuel or lubricants) are non-selective poisoning components for the function of generating the exothermic effect of oxidation catalysts in active or active-passive systems described in the applicant's publication WO 2013/088152 A1. Toxic substances that chemically react with the catalyst components (mechanism (i)) include (at a higher temperature) phosphorus, which can also poison the function of generating an exothermic effect of the oxidation catalyst. The main source of phosphorus and zinc in the exhaust gas is likely to be zinc dialkyldithiophosphate (ZDDP) additives used in mineral oils or zinc dithiophosphate (ZDTP) in synthetic oil. These additives are used to protect moving parts of the engine, such as the camshaft, from wear during operation. High performance vehicle engine oils have higher concentrations of additives than lubricants designed for low power vehicle engines such as those used in passenger cars, so zinc and phosphorus deactivation is a particular concern for high performance vehicle engines. Phosphorus and zinc deposits cannot be removed from the catalyst except under conditions where thermal deactivation of the oxidation catalyst and other catalyst components in the exhaust system may occur (i.e. at very high operating temperatures). A review of toxic agents and poisoning mechanisms involving phosphorus and zinc can be found, for example, in A.J.J. Wilkins et al., Platinum Metals Review, 1990, 34(1) 16–24.

The platinum group metals are relatively rare naturally occurring metal elements of high economic value compared to industrial base metals such as copper. Briefly, as of the filing date of this description, the London Metal Exchange spot copper price was $5,463 per tonne, while the London Bullion Market Association spot platinum price was $845 an ounce, equivalent to $29,806,530 US dollars per ton (in metric tons 35,274 ounces). However, the corresponding spot price for palladium was $1,968 an ounce. Thus, palladium is currently more than twice as expensive as platinum. Thus, there is a general interest in reducing the amount of palladium in diesel oxidation catalysts relative to platinum and, if possible, in reducing the amount of platinum group metals in diesel oxidation catalysts by appropriately promoting the use of less expensive metal elements.

The present invention is based on the active or active-passive systems described in the applicant's publication WO 2013/088152 A1 and has the general goal of reducing the total amount of platinum group metals present in the diesel oxidation catalyst, and the more specific goal of reducing the mass fraction of palladium relative to platinum, and/or improving active filter regeneration efficiency by using less fuel to achieve the desired filter inlet end temperature, and/or achieving a higher filter inlet end temperature with the same amount of fuel injected upstream of the oxidation catalyst of the prior art to generate an exothermic effect therein, and/or provide for the generation of an exothermic effect on the oxidation catalyst at a lower initial temperature of the exhaust gas at the inlet of the oxidation catalyst. In addition, the inventors have developed a composite oxidation catalyst, i.e. a multifunctional single support catalyst design, wherein one or more of the above objectives can be combined with stable NO ₂ generation to operate downstream catalyst functions, including a ^CRT® effect for burning particulates on the downstream filter and/or promoting so-called fast reaction on a selective catalytic reduction (SCR) catalyst. An additional advantage of the preferred design is a multifunctional catalyst having improved control of hydrocarbon slippage. In a preferred design, in addition to one or more or all of the above benefits, a protective layer may be included in the composite oxidation catalyst configuration to reduce or prevent phosphorus and/or zinc poisoning of the catalyst from engine lubrication additives and thereby essentially maintain the efficiency of the catalyst, ie. its durability, for a longer period.

Statement of the Invention

The present inventors surprisingly found that the combination of platinum and palladium PGM components equivalent in weight or platinum-dominated with an alkaline earth metal component in a porous oxide catalytic coating zone at the upstream end of an oxidation catalyst located upstream of the filter substrate in a compression ignition vehicle engine system, in particular a heavy duty diesel engine, provides one or more of the desired improvements.

According to a first aspect, the invention provides a composite oxidation catalyst for use in an exhaust system for purifying exhaust gas produced by an internal combustion engine for a compression ignition vehicle, preferably for a heavy duty diesel vehicle, and disposed in the exhaust system upstream of the particulate filter, wherein the composite oxidation catalyst comprises:

a substrate having an overall length L and a longitudinal axis and having a substrate surface extending in the axial direction between the first end of the substrate and the second end of the substrate; and two or more porous oxide catalytic coating zones arranged in series in the axial direction on and along the surface of the substrate, wherein the first porous oxide catalytic coating zone having a length L ₁ , where L ₁ <L, is formed at one end by the first end substrate, and at the second end - the first end of the second zone of the catalytic coating of the porous oxide, having a length L ₂ , and L ₂ <L, wherein the first zone of the catalytic coating of the porous oxide contains the first substrate material of the heat-resistant metal oxide and two or more deposited on it components representing a metal of the platinum group, containing both platinum and palladium at a mass ratio of platinum and palladium ≥1; and the second porous oxide catalytic coating zone comprises a second refractory metal oxide substrate material and one or more platinum group metal components deposited thereon, wherein the total load of platinum group metals in the first porous oxide catalytic coating zone, expressed in grams platinum group metals per cubic foot of support volume (g/ft ³ ), greater than the total load of platinum group metals in the second porous oxide catalytic coating zone, and wherein the first porous oxide catalytic coating zone contains one or more first components that are alkaline earth a metal, preferably barium, deposited on a first refractory metal oxide support material.

The product of the claims may also be labeled to indicate that the first end of the substrate must be oriented upstream when installed in any of the second through fifth aspects of the invention set forth herein below.

It should be understood that the feature that determines the axial length of the porous oxide catalytic coating zone is the load of platinum group metals in grams of platinum group metals per cubic foot of support volume (g/ft ³ ). Typically, the platinum group metal load at any point along the axial length of the porous oxide catalytic coating zone varies by no more than +/-20% of the average value along the axial length of the zone as a whole, optionally by +/-15%, for example by + /-ten%. Localized load of platinum group metals can be determined using X-ray fluorescence (XRF) or electron probe microanalysis (EPMA).

In accordance with a second aspect, the invention provides an exhaust system for a compression ignition vehicle engine, comprising a composite oxidation catalyst in accordance with the first aspect of the invention and a particulate filter substrate located downstream of the composite oxidation catalyst, wherein the first end of the catalyst substrate oxidation is oriented to the upstream side.

According to a third aspect, the invention provides a compression ignition internal combustion engine for a heavy duty diesel vehicle, comprising an exhaust system according to the second aspect of the invention, wherein the first end of the composite oxidation catalyst substrate is oriented to the side, located upstream.

According to a fourth aspect, the invention provides a heavy duty diesel engine vehicle comprising an exhaust system according to the third aspect of the invention, i.e. corresponding to any local definition of a heavy duty vehicle as described above. Thus, for example, where the present application is being processed in the United States of America, the United States definition of a heavy duty vehicle in the Background of the Invention section above applies. Likewise, if an application is being considered by the European Patent Office, the relevant EU definition of a heavy duty vehicle from the Background of the Invention section above, etc., applies.

According to a fifth aspect, the invention provides the use of the composite oxidation catalyst according to the first aspect of the invention for heating a particulate filter located downstream of the composite oxidation catalyst in the exhaust system of a compression ignition vehicle engine by generating an exothermic effect as a result of increasing the concentration of hydrocarbon fuel in the exhaust gas flowing through the exhaust system, compared to normal operating conditions by bringing the composite oxidation catalyst into contact with the exhaust gas containing an increased concentration of hydrocarbon fuel.

According to a sixth aspect, the invention provides a method for producing a composite oxidation catalyst, optionally a composite oxidation catalyst according to the first aspect of the invention, for use in an exhaust gas system for purifying exhaust gas produced by an internal combustion engine for a compression ignition vehicle, wherein the composite oxidation catalyst has an overall length L and a longitudinal axis, and has a support surface extending in the axial direction between the first end of the support and the second end of the support; and two or more porous oxide catalytic coating zones arranged in series in the axial direction on and along the surface of the substrate, wherein the first porous oxide catalytic coating zone having a length L ₁ , where L ₁ <L, is formed at one end by the first end substrate, and at the second end - the first end of the second zone of the catalytic coating of the porous oxide, having a length L ₂ , and L ₂ <L, wherein the first zone of the catalytic coating of the porous oxide contains the first substrate material of the heat-resistant metal oxide and two or more deposited on it components representing a metal of the platinum group, containing both platinum and palladium at a mass ratio of platinum and palladium ≥1; and the second porous oxide catalytic coating zone comprises a second refractory metal oxide substrate material and one or more platinum group metal components deposited thereon, wherein the total load of platinum group metals in the first porous oxide catalytic coating zone, expressed in grams platinum group metals per cubic foot of support volume (g/ft ³ ), greater than the total load of platinum group metals in the second porous oxide catalytic coating zone, and wherein the first porous oxide catalytic coating zone contains one or more first components that are alkaline earth a metal, preferably barium, deposited on a first refractory metal oxide support material, the method comprising the steps of:

(a) depositing a catalytic porous oxide coating layer on the surface of a substrate from one end of the substrate, the catalytic porous oxide coating layer comprising a heat resistant metal oxide substrate material and one or more platinum group metal components; and

(b) impregnating the catalytic porous oxide coating layer in a zone of length L ₁ formed at one end by the first end of the support with a solution containing one or more platinum group metals,

wherein one or more alkaline earth metal components are present in the porous oxide catalytic coating layer in step (a) and/or in the impregnation solution used in step (b). It should be understood that the porous oxide catalytic coating layer from step (a) may contain a platinum component, a palladium component, or both platinum and palladium components, and the solution from step (b) may contain platinum, palladium, or both platinum and palladium. provided that the combination of steps (a) and (b) provides a first porous oxide catalytic coating zone having a length L ₁ and containing two or more deposited platinum group metal components containing both platinum and palladium, when the mass ratio of platinum and palladium ≥1.

In a seventh aspect, a composite oxidation catalyst in accordance with the invention may be defined as a product obtained or made possible to obtain by the method in accordance with the sixth aspect of the invention.

More specific elements of aspects of the invention may improve the durability of the composite oxidation catalyst in terms of ability to cope with phosphorus and/or zinc poisoning from engine lubricants, improve control of NO oxidation in downstream processes such as selective catalytic reduction of oxides of nitrogen (NO _x ), and reduce costs by limiting the relative amounts of palladium in the inventive oxidation catalyst composite compared to platinum.

The present invention will be further described below. The following sections describe various aspects of the invention in more detail. Each described aspect can be combined with any other aspect or aspects, unless explicitly stated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Description of graphic materials

On FIG. 1 shows a composite oxidation catalyst (12) according to the invention, comprising a first porous oxide catalytic coating zone (1) located at the inlet end (I) of a flow-through honeycomb substrate monolith (5) having an overall length L, and a second zone (2) a porous oxide catalytic coating adjacent to the first porous oxide catalytic coating zone (1) and located at the outlet end (O) of the substrate (5), wherein the first and second porous oxide catalytic coating zones are arranged in series on the surface of the substrate and along it. Thus, in use, the oxidation catalyst composite substrate is oriented such that exhaust gas from the engine first enters the oxidation catalyst composite through the inlet (or upstream) end (I) and exits the oxidation catalyst composite through the exhaust (or downstream) end. flow) end (O), and the exhaust gas flow is indicated by an arrow numbered 10. The same orientation and order of contacting the composite oxidation catalyst with the exhaust gas is used in all the embodiments described in FIG. 1-5 inclusive, and presented in this document.

The composite oxidation catalyst shown in FIG. 1 can be made by coating the substrate (5) over its entire axial length L with a first porous oxide catalyst layer comprising a first heat-resistant metal oxide substrate material and an aqueous solution of one or more salts of platinum group metals, drying and firing coated parts; and then impregnating only a portion of the substrate coated with the first porous oxide catalytic coating for a length L ₁ , L ₁ < L, with an aqueous solution with a relatively high concentration of one or more platinum group metals and optionally one or more alkaline earth metal components, to form a first zone (1) of the porous oxide catalytic coating, wherein the second catalytic porous oxide coating (2) comprises an unimpregnated first porous oxide catalytic coating layer. In an alternative embodiment, the first porous oxide catalytic coating layer may contain one or more alkaline earth metal components in place of the alkaline earth metal components present in the impregnation medium. Of course, the alkaline earth metal components may also be present in both the impregnation medium and the first porous oxide catalytic coating layer. A description of "impregnation" techniques is provided later in this document. The configuration is provided such that in the finished product, a portion of the first catalytic porous oxide coating layer having a length L ₁ contains two or more platinum group metal components deposited on the substrate material, containing both platinum and palladium, at a mass ratio of platinum and palladium ≥ 1.

In an alternative embodiment, the composite oxidation catalyst shown in FIG. 1 can be or can be made by depositing on the substrate (5) in any order from its first end a first porous oxide catalytic layer to form a first porous oxide catalytic coating zone comprising a first refractory oxide substrate material. metal, two or more platinum group metal components containing both platinum and palladium, such as platinum and palladium being the only platinum group metal components, and one or more alkaline earth metal components, for an axial length L ₁ (see element marked 9 in Fig. 1); and a second, different porous oxide catalytic layer comprising a second refractory metal oxide support material, one or more second platinum group metals, and optionally one or more second alkaline earth metal components to form a second oxidation catalyst zone (see element 11) by an axial length L ₂ , so that the second end (13) of the first porous oxide catalytic layer (9) and the first end (15) of the second (11) porous oxide coating catalytic layer are adjacent to each other without overlapping between first and second porous oxide coating layers. In the latter method for obtaining the embodiment shown in FIG. 1, it should be understood that the axial length of the first zone L _{1 of} the catalytic porous oxide coating is equal to or substantially equal to the axial length of the first catalytic layer (9) of the porous oxide coating; and the axial length of the second zone L _{2 of} the catalytic porous oxide coating is equal to or substantially equal to the axial length of the second zone L _{2 of} the catalytic porous oxide coating.

On FIG. 1 and in each of the embodiments shown in FIG. 2 to 5 inclusive, there is a preferred optional element: a porous outer porous oxide coating layer covering the first zone (1) of the porous oxide catalytic coating, as a protective layer to reduce or prevent poisoning of the first zone of the porous oxide catalytic coating with deposits of phosphorus and / or zinc derived from lubricant additives such as ZDDP or ZDTP. The optional protective layer (G) is shown in dotted lines in each of the embodiments shown in FIG. 1–5, inclusive.

On FIG. 2 and 3 show composite oxidation catalysts (14, 16 respectively) according to the invention, based on the same production principle, i.e. the second layer (7) of the porous oxide catalytic coating is applied from the second end corresponding to the outlet end (O) of the substrate (5) to an axial length L ₄ that is less than the total axial length L (i.e. L ₄ <L) of the flow monolith (5) honeycomb substrates. The second porous oxide catalytic coating layer comprises a second heat resistant metal oxide substrate material and one or more platinum group metal components and optionally one or more second alkaline earth metal components. The substrate coated with the second porous oxide catalytic coating layer (7) is then itself coated with the first porous oxide catalytic coating layer (6) from the opposite end of the substrate (5) corresponding to the inlet or the first end (I) of the substrate, to the point from which a second porous oxide catalytic coating layer was deposited on the substrate (5). The first porous oxide catalytic coating layer comprises a first refractory metal oxide substrate material, one or more platinum group metal components, and optionally one or more first alkaline earth metal components. The axial length (L ₃ ) of the coating from the first porous oxide catalytic coating layer (6) is less than the total axial length L of the substrate, but it is sufficient to overlap with the length (L ₄ ) of the second porous oxide catalytic coating layer (7) to form a region in which the first (6) and second (7) porous oxide catalytic coating layers are present in a two-layer structure: in other words, a "zone". The axial length of the overlap zone of the first porous oxide coating layer and the second porous oxide coating layer can be defined as "L ₅ " and shown as "2" in FIG. 2, i.e. the second zone of the catalytic coating of the porous oxide; and as "4" in FIG. 3, i.e. the fourth zone of the porous oxide catalytic coating.

It can be seen that the zone of length L ₅ having the overlap of the first (6) and second (7) porous oxide catalytic coating layers contains the sum of the amounts of one or more platinum group metals and optionally one or more alkaline earth metals present both in the first layer ( 6) porous oxide catalytic coating, and in the second (7) layer of porous oxide catalytic coating in the overlap area. In addition, it can be seen that since the overlap area of the first (6) and second (7) layers of the porous oxide catalytic coating is a separate zone, the zone (indicated as 3 in both Fig. 2 and 3) containing one layer from the second layer (7) a porous oxide catalytic coating, and formed at the first end (17) by the second (downstream or outlet) end of the overlap region of the first (6) and second (7) layers of the porous oxide catalytic coating, and at the second end - the second end of the substrate (or outlet end (O)) will have a lower total platinum group metal load than the immediately preceding adjacent upstream overlap zone (zone 2 in FIG. 2; and zone 4 in FIG. 3).

In the design shown in Fig. 2, the overlap zone of the first (6) and second (7) porous oxide catalytic coating layers is the second porous oxide catalytic coating zone (labeled 2 in FIG. 2). Part of the total length of the first layer (6) of the porous oxide catalytic coating, which is the first zone of the porous oxide catalytic coating (denoted 1) and is formed at the first end by the inlet / first end (I) of the substrate, and at the second end by the first ( located upstream, i.e. closest to the inlet end) end (19) of the second zone (2) of the porous oxide catalytic coating, and the point also corresponds to the first or upstream end of the second layer (7) of the porous oxide catalytic coating , has a greater total load of platinum group metals (in g/ft ³ ) than the second zone (2) of the porous oxide catalytic coating. In addition, it can be seen that since zone 2 shown in FIG. 2 comprises an overlap of the first (6) and second (7) porous oxide coating layers, the axial length L _{3 of} the first layer (6) of the porous oxide catalytic coating is equivalent to the sum of the axial lengths of the first (1) and second (2) zones of the catalytic coating of porous oxide. In addition, the length of the first porous oxide catalytic coating layer (6) present in the first porous oxide coating zone (1) is the total length of the porous oxide catalytic coating layer 6 minus the length of the first porous oxide coating layer located in overlap zone 2, i.e. L ₅ .

In practice, the feature of the total platinum group metal loading of the first zone (1) of the catalytic porous oxide coating, which exceeds the total load of platinum group metals of the second zone (2) of the catalytic porous oxide coating, in each of the embodiments as shown in FIG. 2-5 inclusive can be obtained by impregnating the desired length (8) L( ₁ ) of the underlying first porous oxide catalytic layer (6) with a relatively high concentration of salts of platinum group metals, for example, their aqueous solution, optionally also containing aqueous salts of one or more alkaline earth metals. "Impregnation" is a method known to the person skilled in the art and described, for example, in Catalytic Air Pollution Control - Commercial Technology, 3rd ^Edition , Ronald M. Heck et al., John Wiley & Sons, Inc. (2009) at point 2.3. On FIG. 2, the axial length L _{1 of} the first porous oxide catalytic coating zone (denoted 1) is essentially the length of the first porous oxide catalytic coating layer (6) up to the point at which the first porous oxide catalytic coating layer (6) begins to overlap the second layer. (7) porous oxide catalytic coating at point 19.

If the porous oxide coating for forming the first layer (6) of the catalytic porous oxide coating does not contain platinum and palladium, for example, the impregnation medium should contain dissolved salts of palladium or platinum, which are not present in the first layer (6) of the catalytic porous oxide coating, so so that the required length (8) (L ₁ ) of the underlying first porous oxide catalytic coating layer contains two or more deposited platinum group metal components containing both platinum and palladium, with a mass ratio of platinum to palladium ≥1. Of course, in any combination, the first porous oxide catalytic coating layer itself may contain platinum, palladium, or both platinum and palladium; and separately, the impregnation medium may contain platinum, palladium, or both platinum and palladium, i. e. the content of PGM in the first porous oxide catalytic coating layer and in the impregnation medium may be the same or different, provided that in the end the desired length (8) (L ₁ ) of the underlying first porous oxide catalytic coating layer will contain two or more applied to these components, representing a metal of the platinum group, containing both platinum and palladium, with a mass ratio of platinum and palladium ≥1. If the porous oxide coating for forming the first layer (6) of the catalytic porous oxide coating does not contain one or more alkaline earth metal components, for example, the impregnation medium must contain salts of one or more alkaline earth metals. It is, of course, also possible that both the porous oxide coating forming the first layer (6) of the catalytic porous oxide coating and the impregnation medium contain one or more alkaline earth metals, in which case the alkaline earth metal or metals in the porous oxide coating composition and in impregnation medium may be the same or different.

The third zone of the porous oxide catalytic coating (denoted 3) is formed at its second (or outlet (O)) end by the second end of the substrate and has an axial length L ₆ . First end, i.e. closest to the first (or inlet (I)) end of the substrate, the third zone (3) of the porous oxide catalytic coating, described above in this document as (17).

From the configuration shown in Fig. 2 and from the description above herein, it can be seen that each porous oxide catalytic coating zone may be partially formed by only a portion of the axial length of the porous oxide catalytic coating layer. Thus, the underlying refractory metal oxide substrate material is present in the porous oxide catalytic coating zone of which the porous oxide catalytic coating layer is a part. It follows that if the porous oxide catalytic coating zone has an overlap of porous oxide catalytic coating layers, then the refractory metal oxide substrate material in the porous oxide catalytic coating zone formed as a result of the overlap comprises a refractory metal oxide substrate in each from porous oxide catalytic coating layers present at the overlap. Thus, if the refractory metal oxide substrate material in the first porous oxide catalytic coating layer in the overlap zone is different from the refractory metal oxide substrate material in the second porous oxide catalytic coating layer, in the overlap zone of porous oxide catalytic coatings as a whole two (or more) refractory metal oxide substrate materials will be present. It is, of course, also possible for a single porous oxide catalytic coating layer to comprise two or more different refractory metal oxide substrate materials, in which case the porous oxide catalytic coating zone formed from this single porous oxide catalytic coating layer would be contain two or more different heat-resistant metal oxide substrate materials. Similarly, if the refractory metal oxide substrate material is the same in each of the two porous oxide catalytic coating layers that form the porous oxide catalytic coating zone on the substrate by overlapping, only one material will be present in the porous oxide catalytic coating zone. heat-resistant metal oxide substrate.

The configuration shown in Fig. 3 is similar to that shown in FIG. 2 and described above herein, except that the axial length L _{1 of} the first zone of the porous oxide catalytic coating (denoted 1) is the smaller length of one first layer (6) of the porous oxide catalytic coating, formed, for example, by impregnation a shorter length (8) of the substrate (5) coated with a first layer of catalytic porous oxide coating (6) with a relatively high concentration of an aqueous solution of one or more platinum group metal salts and optionally also salts of one or more alkaline earth metals. In this embodiment, a second porous oxide catalytic coating zone (denoted 2) is formed at the first end, i. closest to the first or inlet end of the substrate, the second end (21) of the first zone 1 of the catalytic coating of porous oxide, for example, the length of impregnation (8) of the first layer (6) of the catalytic coating of porous oxide, and at the second end - the first end (23) an overlap region of the first porous oxide catalytic coating layer (6) with the underlying second porous oxide catalytic coating layer (7) closest to the inlet end (I). The nature of the total load of platinum group metals in the first zone of the porous oxide catalytic coating, which exceeds the total load of platinum group metals in the second zone of the porous oxide catalytic coating, is provided, for example, by impregnation of the underlying first layer of the porous oxide catalytic coating, which contains one or more platinum group metal components with a relatively high concentration of one or more platinum group metals. Such impregnating medium may also include aqueous salts of one or more alkaline earth metals.

In accordance with the definition of the invention, the third porous oxide catalytic coating layer (denoted 3) is formed at its second (or outlet (O)) end by the second end of the substrate. Thus, in the embodiment shown in FIG. 3, a zone consisting of an overlapping point of the first porous oxide catalytic coating layer (6) and the second porous oxide catalytic coating layer (7), which is located in the axial direction between the second zone (2) of the porous oxide catalytic coating and the third zone ( 3) of the porous oxide catalytic coating is numbered as the fourth zone of the porous oxide catalytic coating and is indicated in FIG. 3 with the number "4". On FIG. 3 that the axial length of the first porous oxide coating layer (6) is the sum of the axial lengths of the first (1), second (2), and fourth (4) zones of the porous oxide catalytic coating. In addition, it can be seen that the axial length of zone 2 is the total axial length L _{3 of} the first porous oxide catalytic coating layer (6) minus the axial length of the overlap zone, zone 4, i. e. equivalent to L ₅ and the length L _{1 of} the first zone 1 of the porous oxide catalytic coating. The axial length of zone 3 is formed at its second (outlet (O) or downstream end) by the second end of the substrate and has an axial length L ₆ .

The configurations shown in Fig. 4 and 5 (composite oxidation catalysts 18 and 20, respectively) are similar to those shown in FIG. 2 and 3, respectively, except that in the embodiments shown in FIG. 4 and 5, a first porous oxide coating layer (6) comprising a first refractory metal oxide substrate material and deposited with one or more platinum group metal components and optionally one or more first alkaline earth metal components. applied to the flow monolith (5) substrates with a honeycomb structure, starting from the inlet end (I) to the length L ₃ . The substrate coated with the first porous oxide catalytic coating layer (6) is then itself coated with the second porous oxide catalytic coating layer (7) (i.e. to a length where L ₄ <1) starting from the opposite end of the substrate (5) corresponding to the outlet end (O) and up to the point from which the first porous oxide catalytic coating layer (6) is deposited on the substrate (5). The axial length of the coating for the second layer (7) of the porous oxide catalytic coating is less than the total axial length L of the substrate, but it is sufficient to overlap with the first layer (6) of the porous oxide catalytic coating to form a region in which the second (7) and the first ( 6) a porous oxide catalytic coating layer is present in the two-layer zone. For the avoidance of repetition, Applicant refers the reader to the explanations provided herein above regarding the description of the length of the axial zones, the definitions of the zone boundaries, the total load of platinum group metals in the zones, the description of the refractory metal oxide substrate material in the zones, etc. Similarly.

On FIG. 6 is a schematic representation of one layer, such as the layer of the first zone of a porous oxide catalytic coating, in accordance with embodiments of the invention, which has a uniform or uniform distribution of the first platinum group metal (for example, platinum group metal 1, denoted D) and uneven (t i.e. non-uniform) distribution of the second platinum group metal (for example, platinum group metal 2, denoted by ○).

On FIG. 7 is a schematic diagram showing the uniform distribution of two platinum group metals (e.g., platinum group metal 1, denoted by D, and platinum group metal 2, denoted by ○) in embodiments of a single layer porous oxide catalytic coating zone of the invention.

On FIG. 8A-D show various system designs containing composite oxidation catalysts in accordance with the first aspect of the invention, such as any of those described in each of FIGS. 1–5 inclusive.

Detailed description of the invention

For the avoidance of doubt, the composite oxidation catalyst described herein is referred to as an "oxidation catalyst" because it can oxidize contaminants in the exhaust gas during normal lean burn operation in a compression ignition engine, resulting in a lean exhaust gas, mainly carbon monoxide and unburned hydrocarbons. The composite oxidation catalyst can also oxidize the nitrogen monoxide in the exhaust gas to nitrogen dioxide to promote subsequent catalytic activity, such as a ^CRT® effect, and/or promote a selective catalytic reduction reaction, and such NO oxidizing activity can be enhanced by exploiting the features of one or more dependent claims. the claims appended to this document. Since such a catalyst is preferably used for purifying exhaust gases generated by a compression ignition diesel engine, it may also be referred to as a "diesel oxidation catalyst". However, sometimes the composite oxidation catalyst of the present invention is designed to generate an exothermic effect using additional hydrocarbons introduced into the exhaust gas, which heats the downstream particulate filter and regenerates it (i.e., burns off the soot it has trapped ( active regeneration.

The activity of the composite oxidation catalyst is not limited to oxidation reactions, although the oxidation catalyst must be capable of oxidizing one or more contaminants in the exhaust gas of a compression ignition engine during normal lean burn operation. For example, under appropriate conditions, the oxidation catalyst may be further capable of carrying out a reduction reaction, such as the reduction of oxides of nitrogen (NO _x ), using a hydrocarbon in the exhaust gas as a reducing agent (so-called NO _x catalysis for lean conditions, DeNO _x catalysis, or hydrocarbons). -SCR) and/or may be capable of temporarily storing one or more pollutants from the exhaust gas, such as temporarily _adsorbing NOx and/or hydrocarbons. For the avoidance of further doubt, it should be noted that the use of a composite oxidation catalyst to generate an exothermic effect using additional hydrocarbon fuel injected into the exhaust gas is not "normal use" (see the description of the frequency of regenerations in the "Background of the Invention" section above in this document ). Thus, a "normal lean burn operation" is the period between exothermic generation events.

With respect to NO oxidative activity, the overall oxidation catalyst composite preferably promotes NO oxidation for a period of >10% of the operating range of the oxidation catalyst during normal use, such as >20%, >30%, >40%, or >50%. This differs markedly from the oxidation catalyst described in WO 2009/076574 discussed above herein, wherein the diesel oxidation catalyst substantially produces no additional NO ₂ to the exhaust gas stream after it has passed through the diesel oxidation catalyst for a period of about 90% of the operating range of the diesel oxidation catalyst. The composite oxidation catalyst of the present invention accomplishes this by including at least one oxidation catalyst zone having a weight ratio of platinum to palladium >1, such as >1.5:1 or >2:1, optionally only platinum as the only platinum group metal present in that particular zone, i.e. the mass ratio of platinum and palladium is 1 : 0 (or "infinity" (∞)). In the case of porous oxide catalytic coating zones other than the first porous oxide catalytic coating zone, such other zones may optionally exhibit increased NO oxidation when a lower alkaline earth metal load is present in the zone or zones other than the first porous oxide catalytic coating zone. or essentially no alkaline earth metal.

According to a first aspect, a second porous oxide catalytic coating zone may be formed at its second end by a second end of the substrate. Thus, the composite oxidation catalyst generally comprises two porous oxide catalytic coating zones (see, for example, the configuration shown in FIG. 1).

Methods for producing such a catalyst having two zones of porous oxide catalytic coating include the method according to the sixth aspect of the invention, wherein in step (a) the porous oxide catalytic coating extends along the entire length L of the substrate. It should be understood that in this method, the first refractory metal oxide substrate material is similar to the second refractory metal oxide substrate material. In an alternative embodiment, the composite oxidation catalyst shown in FIG. 1 can be obtained or can be made possible to obtain by depositing on the substrate (5) in any order from its first end the first porous oxide catalytic layer to form the first zone of the porous oxide catalytic coating, and containing the first substrate material of heat-resistant metal oxide, two or more platinum group metal components containing both platinum and palladium, and one or more alkaline earth metal components over an axial length L ₁ (see element labeled 9 in FIG. 1) ; and a second, different porous oxide catalytic layer comprising a second refractory metal oxide support material, one or more second platinum group metals, and optionally one or more second alkaline earth metal components to form a second oxidation catalyst zone (see element 11) by an axial length L ₂ , so that the second end (13) of the first porous oxide catalytic layer (9) and the first end (15) of the second (11) porous oxide coating catalytic layer are adjacent to each other without overlapping between first and second porous oxide coating layers. In the latter method for obtaining the embodiment shown in FIG. 1, it should be understood that the axial length of the first zone L _{1 of} the catalytic porous oxide coating is equal to or substantially equal to the axial length of the first catalytic layer (9) of the porous oxide coating; and the axial length of the second zone L _{2 of} the catalytic porous oxide coating is equal to or substantially equal to the axial length of the second zone L _{2 of} the catalytic porous oxide coating. Further information on methods for preparing a two-zone composite oxidation catalyst in accordance with the first aspect of the invention is given above in this document with reference to FIG. one.

In an alternative embodiment according to the first aspect, the composite oxidation catalyst may comprise three or more porous oxide catalytic coating zones, wherein a third porous oxide catalytic coating zone comprising a third refractory metal oxide support material and one or more components deposited thereon , which is a platinum group metal, is formed at its second end by the second end of the substrate, and the total load of platinum group metals in the third zone of the porous oxide catalytic coating, expressed in grams of platinum group metal per cubic foot of support volume (g/ft ³ ) , less than the total load of platinum group metals in the second zone of the porous oxide catalytic coating.

The composite oxidation catalyst according to the first aspect of the invention may comprise four porous oxide catalytic coating zones, wherein the fourth porous oxide catalytic coating zone is located between the second porous oxide catalytic coating zone and the third porous oxide catalytic coating zone, the fourth catalytic coating zone from porous oxide contains a fourth material-substrate of heat-resistant metal oxide and one or more components deposited on it, representing a platinum group metal, and is formed at the first end by the second end of the second zone of the porous oxide catalytic coating, and at the second end by the first end of the third porous oxide catalytic coating zone, and wherein the total platinum group metal load in the fourth porous oxide catalytic coating zone, expressed in grams of platinum group metal per cubic foot of substrate volume (g/ft ³ ), is greater than the total load of platinum group metals in each of the second porous oxide catalytic coating zone and the third porous oxide catalytic coating zone.

Preferably, the oxidation catalyst composite according to the first aspect of the invention comprises four porous oxide catalytic coating zones, wherein the composite oxidation catalyst comprises a first porous oxide catalytic coating layer and a second porous oxide catalytic coating layer, wherein the first porous oxide catalytic coating layer the oxide comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₃ , with L ₃ <L, and is formed at one end by the first end of the substrate; and the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₄ , where L ₄ <L, and is formed at the second end by the second end of the substrate , wherein the fourth zone of the porous oxide catalytic coating contains a two-layer region of overlap of the first layer of the porous oxide catalytic coating and the second layer of the porous oxide catalytic coating, and the third zone of the porous oxide catalytic coating contains one layer of the second layer of the porous oxide catalytic coating A that is not formed from the overlap region. Methods for making such a composite oxidation catalyst are described above herein with reference to the embodiments shown in FIG. 3 and 5, and with additional reference to the embodiments shown in FIG. 2 and 4 and related descriptions.

The composite oxidation catalyst comprising three porous oxide catalytic coating zones may have a third porous oxide catalytic coating zone formed at its first end by a second end of the second porous oxide catalytic coating zone (see, for example, the configurations shown in FIG. 2 and 4).

Such a composite oxidation catalyst may comprise a first porous oxide catalytic coating layer and a second porous oxide catalytic coating layer, wherein the first porous oxide catalytic coating layer comprises a refractory metal oxide support material and one or more supported metal components. platinum group, has a length L ₃ with L ₃ <L, and is formed at one end by the first end of the substrate; and the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₄ , with L ₄ <L and is formed at the second end by the second end of the substrate, wherein the second porous oxide catalytic coating zone comprises a two-layer overlapping region of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer, and the third porous oxide catalytic coating zone comprises one layer of the second porous oxide catalytic coating layer, which is not formed from the overlap area.

In the three and four zone configurations described herein above, it is preferred that one or more platinum group metal components in the third zone of the porous oxide catalytic coating consist essentially of platinum. It should be understood that if one or more of the platinum group metals in the third zone of the porous oxide catalytic coating consist essentially of platinum, then in configurations involving overlapping of the first and second porous oxide catalytic coating layers, the second porous oxide catalytic coating layer, which forms the third zone of the porous oxide catalytic coating, also consists essentially of platinum.

Additionally, it should be understood that in composite oxidation catalysts having two zones as described herein, the second zone of the porous oxide catalytic coating may contain one or more alkaline earth metals such as barium and/or strontium, preferably barium.

It should also be understood that in composite oxidation catalysts having three zones as described herein, each of a second porous oxide catalytic coating zone, a third porous oxide catalytic coating zone, or both a second porous oxide catalytic coating zone, and a third zone The porous oxide catalytic coating may contain one or more alkaline earth metals such as barium and/or strontium, preferably barium.

It is further to be understood that in composite oxidation catalysts having four zones as described herein, each of the second porous oxide catalytic coating zone, the third porous oxide catalytic coating zone, and/or the fourth porous oxide catalytic coating zone may comprise one or more alkaline earth metals such as barium and/or strontium, preferably barium.

Additionally, it should be understood that in composite oxidation catalysts having three or four zones as described herein, each of the first porous oxide catalytic coating layer, the second porous oxide catalytic coating layer, and/or both the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer may contain one or more alkaline earth metals such as barium and/or strontium, preferably barium.

Methods for producing three- or four-zone composite oxidation catalysts in accordance with the invention include a method in accordance with the sixth aspect of the invention, in which in step (a) the porous oxide catalytic coating layer is a first porous oxide catalytic coating layer that extends from the first end of the substrate to a length less than the total length of the substrate, the method further comprising step (a') before step (a) or after step (a), but in any case before step (b) of applying a second layer of porous oxide catalytic coating on the substrate from the second end of the substrate to a length less than the total length of the substrate so that the first porous oxide catalytic coating layer partially overlaps the second porous oxide catalytic coating layer or the second porous oxide catalytic coating layer partially overlaps the first porous oxide catalytic coating layer, and the second catalytic coating layer The porous oxide coating comprises a refractory metal oxide support material and one or more platinum group metal components, it being understood that the composition of the platinum group metals in the porous oxide catalytic coating zone comprising two overlapping layers includes the sum of the amounts platinum group metals present in each of the two overlapping layers of the zone.

If the method described above is used to prepare a composite oxidation catalyst according to the invention having three or more zones, it should be understood that the axial length L ₁ in the impregnation step may determine the number of porous oxide catalytic coating zones present along the axial length of the substrate. This is further explained with reference to FIG. 2, 3, 4 and 5 in this document.

If L ₁ is less than the axial length between the first end of the substrate and the first end of the second porous oxide catalytic coating, which is the end of the overlap region of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer closest to the first end of the substrate, the second catalytic zone The porous oxide coating comprises one layer of the first porous oxide catalytic coating formed at one end by the second end of the _first porous oxide catalytic coating zone L a coating of porous oxide closest to the first end of the substrate. In this case, the fourth porous oxide catalytic coating zone is formed by the first end of the overlap region of the first and second porous oxide coating layers closest to the first end of the substrate, wherein the platinum group metal loading in the first porous oxide catalytic coating zone (g/ft ³ ) > fourth porous oxide catalytic coating zone > second porous oxide catalytic coating zone. The third porous oxide catalytic coating zone is formed at the second end by the end of the substrate opposite to the end of the substrate from which the first porous oxide catalytic coating layer extends, and at the first end by the end of the overlap region of the first porous oxide catalytic coating layer and the second catalytic coating layer of porous oxide closest to the end from which the second porous oxide catalytic coating extends, i. e. also corresponds to the second end of the fourth zone of the porous oxide catalytic coating. The design is shown in Fig. 3 and 5 in this document.

Moreover, the length L ₁ coincides with the axial length of one layer of the first porous oxide catalytic coating extending from the first end of the substrate to the place where the first porous oxide catalytic coating layer enters the overlap region with the second zone of the porous oxide catalytic coating, and the oxidation catalyst in generally contains three axially located porous oxide catalytic coating zones, which can be sequentially numbered from the first end of the substrate as the first, second and third porous oxide catalytic coating zones.

In an alternative embodiment, an oxidation catalyst having three or more porous oxide catalytic coating zones in accordance with the invention can be manufactured in accordance with the method for producing an oxidation catalyst according to the sixth aspect of the invention with two porous oxide catalytic coating zones described herein above. , in the following way. First, a first porous oxide catalytic coating layer is applied to the substrate along its entire length L. Secondly, a second porous oxide catalytic coating layer comprising a heat-resistant metal oxide substrate material and one or more group may be applied from the first end of the substrate over the first porous oxide catalytic coating layer to an axial length less than the overall length of the substrate L or alternatively, the first porous oxide catalytic coating layer may be impregnated from the first end of the substrate with the impregnation solution containing one or more platinum group metal salts and optionally one or more alkaline earth metal salts to a length that is less than the total length L of the substrate. The second porous oxide catalytic coating layer or the impregnated first porous oxide catalytic coating layer partially forms the middle or second of the three porous oxide catalytic coating zones axially along the substrate. Third, a third porous oxide catalytic coating layer comprising a heat-resistant metal oxide substrate material and one or more platinum group metal components constituting the first zone L ₁ of the porous oxide catalytic coating can be coated from the first end substrates over the second porous oxide catalytic coating layer (or otherwise impregnated over the impregnated first porous oxide coating layer for a zone length L ₁ corresponding to the first porous oxide catalytic coating zone) to an axial length that is less than the length of the second porous oxide catalytic coating layer , or less than the axial length of the first impregnation from the second step above. It should be understood that the content of platinum group metals in the first zone L ₁ of the porous oxide catalytic coating provides for a combination of the composition of the platinum group metals of the underlying first porous oxide catalytic coating layer, the second porous oxide catalytic coating layer or impregnation solution, and the third catalytic coating layer of porous oxide or impregnation solution, provided that in L ₁ as a whole, the combination of layers and impregnation solutions contains platinum and palladium in a mass ratio of ≥1. One or more alkaline earth metal components may be present in the porous oxide coating or impregnation step of the first, second and/or third deposition steps.

It is preferable to carry out at least the third stage as an impregnation to a length L ₁ corresponding to stage (b) of the sixth aspect of the invention. This is due to the fact that a plurality of coating layers deposited on top of each other reduce the cross-sectional area of the substrate open in the frontal region for the passage of gas and thereby increase the back pressure in the system. Thus, a composite oxidation catalyst is preferred in which at least one porous oxide catalytic coating zone is formed in the step of impregnating the underlying layer of the porous oxide catalytic coating, preferably in the third step corresponding to the formation of the first porous oxide catalytic coating zone.

During operation in the exhaust system of a compression ignition vehicle engine, the first end of the oxidation catalyst substrate according to the first aspect of the invention, comprising the first porous oxide catalytic coating zone, is oriented upstream, i. closest to the engine. Thus, the first end of the substrate may be defined as the first upstream inlet end of the substrate, and the second end of the substrate may be defined as the second downstream (or outlet) end of the substrate.

Loading with platinum group metals

Generally, each porous oxide catalytic coating zone in the oxidation catalyst composite according to the present invention contains one or more; or two or more platinum group metal components selected from the group consisting of platinum, palladium, rhodium, iridium, ruthenium, and a mixture or alloy of any two or more of them, except in the case of a first porous oxide coating zone, which in according to the first aspect of the invention contains both platinum and palladium in a mass ratio of platinum and palladium ≥1. If the porous oxide catalytic coating zone other than the first porous oxide catalytic coating zone contains only one platinum group metal, it is preferably platinum, i. one or more platinum group metal components consist essentially of or consist of platinum.

In particular, two or more platinum group metal components in the first porous oxide catalytic coating zone and/or the first porous oxide catalytic coating layer contain both platinum and palladium, for example two or more platinum group metal components. , consist predominantly of or consist of platinum and palladium. Preferably, the only platinum group metals present in the first porous oxide catalytic coating zone and/or the first porous oxide catalytic coating layer are platinum and palladium. It should be understood that if the first porous oxide catalytic coating layer contains both platinum and palladium, any porous oxide catalytic coating zone including the first porous oxide catalytic coating layer will also contain both platinum and palladium.

It is further preferred that one or more of the platinum group metal components in the second zone of the porous oxide catalytic coating contain, i. e. intentionally contains platinum, e.g. both platinum and palladium, or platinum may be the only platinum group metal present in the second zone of the porous oxide catalytic coating, e.g. one or more platinum group metal components in the second zone of the porous oxide catalytic coating consist of platinum; or more than one platinum group metal component in the second zone of the catalytic porous oxide coating consists of both platinum and palladium. Optionally, the content of platinum in the second zone of the porous oxide catalytic coating is greater than 1 wt. % of the total amount of metal, including platinum group metals and base metals (e.g., alkaline earth metals) deposited on the refractory metal oxide substrate material in the zone. This feature differs from that set forth in WO 2009/076574, cited above in the "Background of the Invention" section.

If the substrate preferably comprises three or more porous oxide catalytic coating zones, the third porous oxide catalytic coating zone or the second porous oxide catalytic coating layer contains platinum, i. intentionally contains platinum, such as platinum and palladium, or the platinum may be the only platinum group metal present in the third porous oxide catalytic coating zone or the second porous oxide catalytic coating layer. Optionally, the content of platinum in the third zone of the porous oxide catalytic coating is greater than 1 wt % of the total amount of metal, including platinum group metals and base metals (e.g., alkaline earth metals) deposited on the refractory metal oxide substrate material in the zone. This feature differs from that set forth in WO 2009/076574, cited above in the "Background of the Invention" section.

In a preferred design, platinum is the only platinum group metal in the second porous oxide catalytic coating layer, i. one or more platinum group metal components in the second porous oxide catalytic coating layer are composed of platinum (weight ratio P : Pd 1 : 0), since this characteristic provides a more stable formation of NO ₂ for the operation of downstream catalytic functions, in particular, in configurations in which the second porous oxide catalytic coating layer overlaps with the first porous oxide catalytic coating layer, as shown in FIG. 4 and 5. Thus, for stable NO ₂ generation, a configuration is preferred in which one or more platinum group metal components in the second porous oxide catalytic coating layer are composed of platinum, the second porous oxide catalytic coating layer overlaying the first layer of porous oxide catalytic coating. In preferred constructions, in which platinum is the only platinum group metal present in the third zone of the porous oxide catalytic coating or in the second layer of the porous oxide catalytic coating, i. e. the mass ratio of Pt : Pd is 1 : 0, the third zone of the porous oxide catalytic coating or the second layer of the porous oxide catalytic coating contains manganese (see below in this document).

Preferably, the second zone of the porous oxide catalytic coating contains both platinum and palladium, for example, more than one platinum group metal component in the second zone of the porous oxide catalytic coating consists of platinum and palladium, since this feature improves the control of hydrocarbon slippage.

Thus, in general, in contrast to the disclosure in WO 2009/076574, cited in the Background section above, in any zone of a porous oxide catalytic coating that is defined at its second end by the second (outlet) end of the substrate, intentionally contains platinum, and optionally the platinum content in the zone of the porous oxide catalytic coating is more than 1 wt.% of the total amount of metal, including platinum group metals and base metals (for example, alkaline earth metals) deposited on a substrate material of a heat-resistant metal oxide in zone.

Typically, the total load of platinum group metals on the substrate as a whole (calculated as elemental metal) is 5 to 60 g/ft ³ , preferably 8 to 50 g/ft ³ for heavy duty diesel engine exhaust systems. conditions.

The weight ratio of Pt : Pd on the substrate as a whole (calculated as elemental metal) is preferably 3:2 to 9:1, preferably 2:1 to 7:1, most preferably 3:1 to 5:1.

The load of platinum group metals in the first zone of the porous oxide catalytic coating (based on elemental metal) is preferably less than 100 g/ft ³ , preferably 25-75 g/ft ³ , and most preferably 35-65 g/ft ³ . It should be understood that the first porous oxide catalytic coating zone may have an "underlying" load of platinum group metals in the first porous oxide catalytic coating layer in substantially one layer of the first porous oxide catalytic coating, which is subsequently impregnated with a highly concentrated solution of platinum group metal salts. before drying and roasting. As a result, the first porous oxide catalytic coating zone is a combination of the platinum group metal loadings of the first porous oxide catalytic coating layer and the impregnation solution.

Loading with platinum group metals in the second and subsequent zones of the porous oxide catalytic coating as a whole, i.e. The total content of platinum group metals in the porous oxide catalytic coating zones other than the first porous oxide catalytic coating zone (calculated as elemental metal) may depend on the embodiment used. Thus, for example, in embodiments containing only two zones, as shown in FIG. 1, the total load of platinum group metals in the second zone of the porous oxide catalytic coating is preferably from 1 to 10 g/ft ³ .

However, in embodiments comprising three porous oxide catalytic coating zones, wherein the second porous oxide catalytic coating zone comprises an area of overlap of the first and second porous oxide catalytic coating layers (see, for example, the embodiments of FIGS. 2 and 4) , or in embodiments comprising four porous oxide catalytic coating zones, wherein the fourth porous oxide catalytic coating zone comprises an area of overlap of the first and second porous oxide catalytic coating layers (see, for example, the embodiments of FIGS. 3 and 5) ; the total load of platinum group metals in the second (or fourth) zone of the porous oxide catalytic coating may be from 10 to 40 g/ft ³ , preferably from 15 to 35 g/ft ³ .

In embodiments comprising three or four porous oxide catalytic coating zones, such as those shown in any of FIGS. 2-5 inclusive, the total load of platinum group metals in the third zone of the porous oxide catalytic coating can be from 1 to 30 g/ft ³ , preferably from 5 to 20 g/ft ³ .

In embodiments comprising four porous oxide catalytic coating zones, such as those shown in FIG. 3 or 5, the total load of platinum group metals in the second zone of the porous oxide catalytic coating may be from 1 to 30 g/ft ³ , preferably from 5 to 20 g/ft ³ . However, the total load of the porous oxide coating in the second zone of the porous oxide catalytic coating is always higher than in the third zone of the porous oxide catalytic coating.

One or more platinum group metal components deposited on the refractory metal oxide substrate material and/or one or more alkaline earth metal components may be prefixed to the refractory metal oxide substrate material prior to being formed with it. porous oxide coating layer, and thus they will be present in the entire layer of any porous oxide coating coated with such a porous oxide coating. However, in a preferred technique, a dissolved salt of one or more of the platinum group metal components and optionally a dissolved salt of one or more of the first alkaline earth metal components are present, for example, in an aqueous porous oxide coating slurry also containing "fresh" material. refractory metal oxide, and applied to a substrate, and one or more platinum group metal components and one or more first alkaline earth metal components are attached to the refractory metal oxide substrate material through a drying and calcination process after application. porous oxide coating slurry onto the substrate. The term "fresh refractory metal oxide material" means that the platinum group metal component and/or the alkaline earth metal component has not previously been attached to the refractory metal oxide component. This method is preferred due to the lower energy consumption, i.e. due to this, there is no need for a two-step process in which a refractory metal oxide preattached product is first obtained and then this preattached product is used to prepare a porous oxide slurry for coating. In addition, the inventors have found that, in order to generate an exothermic effect, it may be advantageous for at least the first porous oxide catalytic coating layer to have an uneven distribution of one or more platinum group metal components and/or one or more platinum group metal components. is an alkaline earth metal, throughout its thickness (ie, in a direction perpendicular to the surface of the substrate, representing the thickness of the catalyst layer). This advantageous feature is not available or not available to the extent that the desired effect is obtained when the platinum group metal or the alkaline earth metal is prefixed on the heat-resistant metal oxide substrate material.

Explanations of this aspect of the invention of the applicant are given below in this document.

According to a sixth aspect of the invention, also described below, the first porous oxide catalytic coating zone is made or made to be made in part by the steps of:

(a) applying a porous oxide catalytic coating layer to the surface of the substrate to a length from one end of the substrate, the porous oxide catalytic coating layer comprising a refractory metal oxide substrate material and one or more platinum group metal components; and

(b) impregnating the porous oxide catalytic coating layer in a zone of length L ₁ defined at one end by the first end of the support with a solution containing one or more platinum group metals.

Thus, it should be understood that if a porous oxide catalytic coating layer, for example a first porous oxide catalytic coating layer containing one or more platinum group metal components deposited on a refractory metal oxide substrate material, is itself impregnated solution containing one or more platinum group metal components, the platinum group metal composition in the resulting zone is a combination of an underlying porous oxide catalytic coating layer and an impregnating solution. Thus, for example, the weight ratio of platinum to palladium in the first zone of the porous oxide catalytic coating is generally obtained from the total content of platinum and palladium as in the porous oxide catalytic coating layer, i. e. in the first layer of the porous oxide catalytic coating, and in the impregnating solution.

Further, it should be understood that according to the sixth aspect of the invention, in step (a), the porous oxide catalytic coating layer is the first porous oxide catalytic coating layer that extends from the first end of the substrate to a length less than the overall length of the substrate. , the method further comprising step (a') before step (a), but in any case before step (b) of applying a second layer of porous oxide catalytic coating to the substrate from the second end of the substrate to a length less than the total length of the substrate so that the first layer porous oxide catalytic coating partially overlapped the second porous oxide catalytic coating layer or the second porous oxide catalytic coating layer partially overlapped the first porous oxide catalytic coating layer, wherein the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more components which is a metal of the platinum group.

As described above herein with reference to FIG. 4 and 5, preferably the first porous oxide catalytic coating layer extends from the first end of the substrate and the second porous oxide catalytic coating layer extends from the second end of the substrate, wherein the second porous oxide catalytic coating layer partially overlaps the first porous oxide catalytic coating layer. .

In accordance with the present invention, the first zone of the porous oxide catalytic coating contains both platinum (Pt) and palladium (Pd) at a mass ratio of platinum to palladium ≥1. Although there is a general need to reduce the amount of palladium in the composite oxidation catalyst compared to platinum to reduce the overall cost of the platinum group metals in the catalyst, as can be seen from sample 9.5 in example 9 below, applicant's experimental data indicate that from the first zone of the catalytic coating it is undesirable to completely remove palladium from the porous oxide, since this will have a negative impact on the function of generating an exothermic effect of the catalyst during its aging. In this regard, Sample 9.5 in Example 9 shows that if an underlying porous oxide coating layer having a Pt:Pd weight ratio of 2:1 is impregnated with a palladium-free impregnation medium, i. with a mass ratio of Pt : Pd 1 : 0 with the formation of the first zone of the porous oxide catalytic coating, having a mass ratio of Pt : Pd of about 47 : 1, the ability of the obtained catalyst to stimulate the exothermic effect deteriorates, i.e. the first zone of the porous oxide catalytic coating is less resistant to aging. However, although less preferred, Sample 9.5 in Example 9 remains an effective composite oxidation catalyst for the purposes of the present invention.

However, it is substantially preferred that the weight ratio of platinum (Pt) and palladium (Pd) in the first zone of the porous oxide catalytic coating is 10:1 ≥ 1:1, preferably 10:1 ≥ 1.5:1 or 6:1 ≥ 1 .5 : 1, more preferably 4 : 1 ≥ 1.5 : 1, e.g. 6 : 1 ≥ 2 : 1, 4 : 1 ≥ 1.5 : 1 or 2 : 1 ≥ 1 : 1 aged composite oxidation catalysts having a first porous oxide catalytic coating zone obtained by impregnating an underlying porous oxide catalytic coating layer having a weight ratio of Pt : Pd 2 : 1 impregnating medium having a weight ratio of Pt : Pd 1 : 1, 2 : 1, 3 : 1 and 4 : 1. In addition, it was found that in combination with an alkaline earth metal component, the weight ratio characteristic Pt : Pd ≥ 1 : 1 improves ignition temperature exothermic effect a (reducing the ignition temperature), which makes it possible to increase the generation of the exothermic effect at lower exhaust gas temperatures in active and active-passive regeneration systems.

It should be understood that a further reduction in the overall cost of the platinum group metals in the inventive composite oxidation catalyst, with equivalent functionality, can be achieved if the first zone of the porous oxide catalytic coating has a higher Pt : Pd weight ratio (because the present value of the mass of palladium is significantly exceeds the cost of platinum), e.g. at ≥ 1.5 : 1, e.g. in the preferred range of 10 : 1 ≥ 1.5 : 1 or at ≥ 2 : 1 in combination with the fact that the exhaust zone, for example the third zone of the porous oxide catalytic coating , formed at one end by the outlet end of the composite oxidation catalyst support, contains pre-formed manganese-doped mixed magnesium-aluminum oxide. Example 8 shows that a composite oxidation catalyst having an outlet zone of such a composition improves exothermic efficiency and can allow the use of lower amounts of platinum group metal in the outlet zone or the second porous oxide catalytic coating layer partially forming the outlet zone (the third zone of the catalytic coating of porous oxide).

Preferably, particularly in embodiments comprising three or more porous oxide catalytic coating zones, the one or more platinum group metals in the second porous oxide catalytic coating zone contain both platinum and palladium. In a particularly preferred characteristic, the weight ratio of platinum to palladium in the second zone of the catalytic porous oxide coating is greater than the weight ratio of platinum to palladium in the first zone of the catalytic porous oxide coating. In combination with the loading of platinum group metals in the second zone of the porous oxide catalytic coating, the advantage of this Pt : Pd weight ratio in the second zone of the porous oxide catalytic coating is that the catalyst improves hydrocarbon slip control, CO oxidation and NO oxidation.

In this regard, in embodiments consisting of two zones, for example, as shown in FIG. 1 allowing for any overlap by manufacturing methodology (see the "Definitions" section below in this document), it is preferred that the second zone of the porous oxide catalytic coating contain a Pt-rich PGM composition containing palladium, preferably in a weight ratio of ≥ 10 : 1, ≥ 5 : 1, ≥ 3 : 1, or ≥ 2 : 1. In combination with a first porous oxide catalytic coating zone containing Pt : Pd in a ratio ≥ 1 : 1, this characteristic was found to be favorable because it was found that the second zone of the porous oxide catalytic coating containing only Pt (i.e. the mass ratio of Pt : Pd 1 : 0) negatively affects the activation of the exothermic effect and the breakthrough of hydrocarbons in the aged catalyst. Therefore, the presence of Pd in addition to Pt in the second zone of the porous oxide catalytic coating can improve the aging resistance of the second zone of the porous oxide catalytic coating, i. e. maintain oxidative activity during aging. However, in combination with manganese, the Pt : Pd 1 : 0 weight ratio in the second zone of the porous oxide catalytic coating was found to be favorable for NO oxidation (see Example 8 and below herein).

In composite oxidation catalysts according to the invention comprising three porous oxide catalytic coating zones, the preferred weight ratio of platinum to palladium increases from the first porous oxide catalytic coating zone to the second porous oxide catalytic coating zone and to the third porous oxide catalytic coating zone. . This can be achieved, for example, in the embodiments shown in FIG. 2 and 4, in which the second porous oxide catalytic coating layer (7) has a higher Pt:Pd mass ratio than the first porous oxide catalytic coating layer, preferably has a mass ratio of 1:0, i.e. contains only Pt and substantially no Pd, so that one layer of the second porous oxide catalytic coating layer in the third porous oxide catalytic coating zone (3) has the highest Pt : Pd ratio of all porous oxide catalytic coating zones located on substrate. However, the same comments apply here as for composite oxidation catalysts containing only two zones of porous oxide catalytic coating, i.e. the aging resistance of the third zone of the porous oxide catalytic coating can be improved by including some palladium, for example ≥ 10:1, ≥ 5:1, ≥ 3:1, or ≥ 2:1, while maintaining the preferred mass ratio distribution of platinum and palladium increasing from the first porous oxide catalytic coating zone to the second porous oxide catalytic coating zone and to the third porous oxide catalytic coating zone. In the context of three-zone composite oxidation catalysts, the inclusion of manganese in the third zone (3) of the porous oxide catalytic coating is also noted to be beneficial (see example 8 and below in this document).

In addition, in the composite oxidation catalyst having four porous oxide catalytic coating zones, the mass ratio of platinum to palladium in each successive porous oxide catalytic coating zone from the inlet end and sequentially along the length L of the substrate after the first porous oxide catalytic coating zone is larger, than in the immediately preceding zone of the porous oxide catalytic coating. This can also be achieved, for example, in the embodiments shown in FIG. 3 and 5, in which the second porous oxide catalytic coating layer (7) has a higher Pt : Pd mass ratio than the first porous oxide catalytic coating layer, preferably has a mass ratio of 1 : 0, i.e. contains only Pt and substantially no Pd, so that one layer of the second porous oxide catalytic coating layer in the third porous oxide catalytic coating zone (3) has the highest Pt:Pd ratio of all porous oxide catalytic coating zones. However, the same comments apply here as for composite oxidation catalysts containing only two zones of porous oxide catalytic coating, i.e. the aging resistance of the third zone of the porous oxide catalytic coating can be improved by including some palladium, for example ≥ 10:1, ≥ 5:1, ≥ 3:1, or ≥ 2:1, while maintaining the preferred mass ratio distribution of platinum and palladium increasing from the first porous oxide catalytic coating zone to the second porous oxide catalytic coating zone and to the third porous oxide catalytic coating zone. In the context of four-zone composite oxidation catalysts, the inclusion of manganese in the third zone (3) of the porous oxide catalytic coating is also noted to be beneficial (see example 8 and below in this document).

It should be understood that in the context of a four-zone composite oxidation catalyst according to the invention, the characteristic "in each successive porous oxide catalytic coating zone located in series along the length of the substrate L after the first zone of porous oxide catalytic coating at the inlet end, the ratio is greater than in the directly preceding porous oxide catalytic coating zone" provides a different numbering order than in the porous oxide catalytic coating zones of FIG. 3 and 5. That is, in FIG. 3 and 5, the following order of numbering of the porous oxide catalytic coating zones from the first porous oxide catalytic coating zone (1) is given: 1→2→4→3. This is because the third zone (3) of the porous oxide catalytic coating is formed at the second end by the second end of the substrate (or outlet end). However, the characteristic that "in each successive porous oxide catalytic coating zone successively along the length L of the substrate after the first inlet end porous oxide catalytic coating zone, the ratio is greater than in the immediately preceding porous oxide catalytic coating zone" requires, for example, that the weight ratio of Pt : Pd in the fourth zone of the catalytic porous oxide coating is greater than that of the immediately preceding second zone (2) of the catalytic porous oxide coating, and that the mass ratio of Pt : Pd in the third zone (3) of the catalytic porous oxide coating was greater than in the immediately preceding fourth zone (4) of the porous oxide catalytic coating.

Preferably, one or more of the platinum group metals in the second zone of the catalytic porous oxide coating contains both platinum and palladium, with a mass ratio of platinum to palladium being > 1:1, preferably 10:1 > 3:2, for example 5:1 > 3 : 2.

Typically, the first zone of the porous oxide catalytic coating or the first layer of the porous oxide catalytic coating does not contain rhodium.

It may be preferred that the second zone of the porous oxide catalytic coating or the second layer of the porous oxide catalytic coating does not contain rhodium.

The third or fourth zone of the porous oxide catalytic coating may not contain rhodium.

In addition, the composite oxidation catalyst according to the invention may be substantially free of rhodium.

The inventors have also found that it is possible to take advantage of an improved exotherm if there is an uneven distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate. This is described in more detail in the section below.

Alkaline earth metal component

It should be understood that the purpose of the alkaline earth metal in the oxidation catalyst composite of the invention is not to store NO _x for subsequent release and reduction in the lean-burn NO _x catalysis process described above. This is done using a specially designed catalyst called a lean NO _x trap (LNT) which may also include components such as alkaline earth metal, platinum group metals and optionally cerium oxide, doped cerium oxide or mixed cerium oxide, but LNT should be used in combination with specially programmed engine control unit. This engine control provides a lean stoichiometric operation during which NO _{x is} absorbed onto the LNT and an operation in which a pulse of enriched exhaust gas containing additional reducing substances such as CO and/or hydrocarbons contacts the LNT and thus desorbs the absorbed NO _x and reduces them by means of a NO _x catalysis reaction under lean mixture conditions on a platinum group metal. When using LNT, the lean/rich cycle frequency is on the order of about 60 seconds lean and 5 seconds rich. LNT desulfation occurs less frequently, but the enrichment period may be longer. However, a specially programmed engine control unit is also required to control the desulfation event.

The composite oxidation catalyst of the present invention may differ from LNT in at least two significant respects. First, LNT is not used in exhaust gas treatment of heavy duty diesel engines, which use SCR catalysts instead. This is primarily because the LNT catalyst for a heavy duty diesel vehicle must be so large that the cost of the required platinum group metals can make the cost of the catalyst unacceptable. Secondly, it is preferable that the composite oxidation catalyst of the present invention is substantially free of cerium oxide, doped cerium oxide, or mixed cerium oxide or composite oxide components.

In accordance with a first aspect of the invention, the first porous oxide catalytic coating zone comprises one or more first alkaline earth metal components supported on a first refractory metal oxide substrate material. The inventors have found that in order to generate an exothermic effect with hydrocarbon fuels, the presence of an alkaline earth metal component, preferably containing barium, improves the HC conversion to such an extent that the amount of one or more platinum group metals in the first porous oxide coating zone can be reduced by about 7 g/ft ³ and still have the same activity. It is believed that the relatively high load of platinum group metals in the first zone of the catalytic porous oxide coating quickly starts and accelerates the exothermic reaction, while the presence of one or more alkaline earth metals stabilizes the PGM, for example, by reducing sintering and improving thermal stability.

One or more alkaline earth metal components in the first zone of the porous oxide catalytic coating is preferably barium (Ba) or strontium (Sr), preferably Ba, for example one or more first alkaline earth metal components in the first zone of the catalytic coating. porous oxide coating consists of barium.

The reasons for preferring barium over other alkaline earth metals are described later in this document in the section "Uneven distribution of the alkaline earth metal component and/or the platinum group metal components in the porous oxide coating layer".

The total load of the alkaline earth metal component in the first zone of the porous oxide catalytic coating may be from 10-100 g/ft ³ based on the elemental metal, preferably 20-80 g/ft ³ . Too much of the alkaline earth metal component can adversely affect the generation of the exothermic effect. In this regard, the ratio of the total weight of the alkaline earth metal component to the total weight of the platinum group metal (PGM) component may be from 1:1 to 1:2, preferably from 1:1 to 50:80.

According to the method of the sixth aspect of the invention, one or more of the first alkaline earth metal components may be present in the porous oxide catalytic coating layer applied in step (a) and/or in the impregnation solution for step (b), but preferably they are present in the porous oxide catalytic coating layer, for example in the first porous oxide catalytic coating layer for step (a) of the sixth aspect of the invention. This is because, if alkaline earth metal salts, such as barium, are present in the impregnation medium for step (b), they may be difficult to control using the pH ranges preferred for the use of platinum group metal salts in the impregnation medium, and therefore may migrate by capillary discharge from the target first zone of the porous oxide coating. Because the final location of the alkaline earth metal in the final product can be better controlled if the alkaline earth metal component is present in the porous oxide coating that is dried and baked after coating, this option is preferred.

It should be understood that if a porous oxide catalytic coating layer, for example a first porous oxide catalytic coating layer containing one or more alkaline earth metals, is applied in step (a) of the sixth aspect of the invention, and the porous oxide catalytic coating layer itself is impregnated solution in step (b) of the sixth aspect of the invention containing one or more alkaline earth metal components, the resulting impregnated zone composition is a combination of the content of the alkaline earth metal component in the underlying porous oxide catalytic coating layer and the impregnating solution.

The second zone of the porous oxide catalytic coating may also contain one or more alkaline earth metal components, preferably containing barium. It may be derived from one or more of the first alkaline earth metal, preferably barium, present in the porous oxide catalytic coating layer of the sixth aspect of the invention from step (a), for example in the first porous oxide catalytic coating layer, or if the composite oxidation catalyst comprises a third or fourth porous oxide catalytic coating zone in a second porous oxide catalytic coating layer. The one or more alkaline earth metal components present in the second porous oxide catalytic coating layer may be referred to herein as one or more second alkaline earth metal components. The third and fourth porous oxide catalytic coating layers may also include one or more second components of an alkaline earth metal, preferably barium.

The inventors have also found that it is possible to take advantage of an improved exothermic effect, at least for the first zone of a porous oxide catalytic coating, if there is an uneven distribution of one or more platinum group metal components and/or one or more first components representing an alkaline earth metal, in a direction perpendicular to the surface of the substrate. This is described in more detail in the section below.

Heat Resistant Metal Oxide Substrate Material

Each of the first, second, third or fourth refractory metal oxide substrate material or refractory metal oxide substrate material of the first and/or second porous oxide catalytic coating layer is typically selected from the group consisting of alumina, magnesium oxide, silica , zirconia, titanium dioxide, cerium dioxide, and a composite oxide or mixed oxide of two or more of them. In principle, any suitable heat resistant metal oxide substrate material can be used as the first refractory metal oxide substrate material. The support material of each of the first, second, third or fourth refractory metal oxide support material or the refractory metal oxide support material of the first or second porous oxide catalyst layer may be the same or different materials. However, it should be understood that if the composite oxidation catalyst shown in FIG. 1 may be one porous oxide coating layer of length L impregnated from the first end to the axial length L ₁ to form a first porous oxide catalytic coating zone (1) and a second porous oxide catalytic coating zone (2), substrate material of heat-resistant metal oxide in the first and second zones of the porous oxide coating will be the same.

Furthermore, in the embodiments comprising three and four porous oxide catalytic coating zones shown in FIG. 2 to 5 inclusive, if the refractory metal oxide support material used in the first porous oxide catalytic coating (6) is designated "X", then since the first, second and (if any) fourth zones of the porous oxide catalytic coating contain only a portion of the entire length L _{3 of} the first porous oxide catalytic coating layer (6), each of the first, second and (if any) fourth porous oxide catalytic coating zones will each contain a heat-resistant metal oxide support material "X", i.e. . the first(s), second(s), and (if any) fourth(s) refractory metal oxide backing material(s) will be the same. Similarly, if the second porous oxide catalytic coating layer (7) in the embodiments shown in FIG. 2-5 contains a refractory metal oxide substrate material, designated "Y", the third porous oxide catalytic coating zone and, if present, the second or fourth porous oxide catalytic coating zones, which contain areas of overlap, will contain only a portion the entire length L _{4 of} the second layer (7) of the porous oxide catalytic coating, and therefore each of these zones will contain material(s)-substrate(s) of heat-resistant metal oxide Y.

Preferably, the refractory metal oxide substrate material is selected from the group consisting of alumina, silica, zirconia, cerium dioxide and composite oxide or a mixed oxide of two or more of them, most preferably selected from the group consisting of alumina, silica and zirconia and a composite oxide or mixed oxide of two or more of them. Mixed oxides or composite oxides include alumina-silica or cerium oxide-zirconium oxide, most preferably alumina-silica. Preferably, the refractory metal oxide substrate material does not contain cerium oxide, or a mixed oxide, or a composite oxide including cerium oxide. More preferably, the heat resistant oxide is selected from the group consisting of alumina, silica, and alumina-silica. The heat-resistant oxide may be alumina. The heat-resistant oxide may be silicon oxide. The heat-resistant oxide may be silica-alumina.

Since the first porous oxide catalytic coating zone comprises one or more first alkaline earth metal components deposited on the first refractory metal oxide substrate material, preferably the first refractory metal oxide substrate material of the first porous oxide catalytic coating zone or underlying catalytic the porous oxide coating, for example the first catalytic porous oxide coating, contains or consists essentially of alumina doped with a heteroatomic component. The heteroatomic component typically contains silicon, manganese (see below), magnesium, barium, lanthanum, cerium, titanium, or zirconium, or a combination of two or more of these. The heteroatomic component may comprise or consist essentially of silicon oxide, manganese oxide, magnesium oxide, barium oxide, lanthanum oxide, cerium oxide, titanium oxide, or zirconium oxide. More preferably, the heteroatom doped alumina is silica doped alumina or magnesium oxide doped alumina or manganese oxide doped alumina. Even more preferably, the heteroatom doped alumina is silica doped alumina. Alumina doped with a heteroatomic component can be prepared using methods known in the art or, for example, the method described in US 5,045,519.

By incorporating a dopant, the refractory metal oxide substrate material can be stabilized or the catalytic reaction of the supported platinum group metal can be stimulated. Generally, the dopant may be selected from the group consisting of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium ( Nd), barium (Ba) and their oxide. As a rule, the dopant is different from the refractory metal oxide (ie, the refractory metal oxide cation). Thus, for example, when the heat-resistant metal oxide is titanium dioxide, the dopant is not titanium or an oxide thereof.

When a refractory metal oxide substrate material is doped with a dopant, typically the refractory metal oxide substrate material has a total dopant content of 0.1 to 10% by weight. Preferably, the total dopant content is 0.25 to 7% by weight, more preferably 2.5 to 6.0% by weight. Preferably the dopant is silica because oxidation catalysts containing such support materials in combination with platinum group metals and alkaline earth metals promote oxidation reactions such as the oxidation of CO and hydrocarbons.

When the refractory metal oxide substrate material is silica-alumina, typically the refractory oxide consists essentially of 20-95 wt. % alumina and 5-80 wt. % silica (e.g., 50-95 wt. % alumina and 5-50 wt.% silica), preferably 35-80 wt.% alumina and from 20-65 wt.% silicon dioxide (for example, 55-80 wt.% alumina and from 20-45 .% silica), even more preferably 45-75 wt.% alumina and 25-55 wt.% silicon dioxide. Mixed oxides of alumina and silicon with a higher content of silicon dioxide, for example with a content of silicon dioxide of approximately 30 wt.%, can generally provide greater stability of the composite oxidation catalyst to sulfur.

When the refractory metal oxide is cerium-zirconium oxide, typically the refractory oxide consists essentially of 20-95 wt% cerium oxide and 5-80 wt% zirconium oxide (for example, 50-95 wt% cerium oxide and 5-50 wt.% zirconium oxide), preferably 35-80 wt.% cerium oxide and 20-65 wt.% zirconium oxide (for example, 55-80 wt.% cerium oxide and 20-45 wt.% zirconium oxide), even more preferably 45-75 wt.% cerium oxide and 25 to 55 wt.% zirconium oxide.

Typically, the first and second porous oxide catalytic coating layers have a content of the first heat-resistant metal oxide substrate material of 0.1 to 3.5 g in ^-3 (e.g., 0.25 to 3.0 g in ^-3 ) , preferably from 0.3 to 2.5 g in ^-3 , even more preferably from 0.5 to 2.0 g in ^-3 and even more preferably from 0.6 to 1.75 g in ^-3 (for example, from 0.75 to 1.5 g in ^-3 ).

In general, refractory metal oxide substrate materials for use in the present invention are in the form of particles. The first substrate material may have a particle size D ₉₀ ≦50 µm, preferably ≦30 µm, and more preferably ≦20 µm (determined by standard laser diffraction techniques). The particle size distribution of the refractory metal oxide substrate material is chosen to promote adhesion to the substrate. The particles are essentially obtained by milling.

In addition, one or each substrate material in each of the first, second, third, or fourth refractory metal oxide substrate material and/or the refractory metal oxide substrate material of the first or second porous oxide catalytic coating may comprise or substantially no contain an adsorbent of hydrocarbons. The hydrocarbon adsorbent may be selected from zeolite, activated charcoal, porous graphite, and a combination of two or more of these. The hydrocarbon adsorbent, if present, is preferably a zeolite, most preferably an aluminosilicate zeolite.

When the support material contains hydrocarbon adsorbent, typically the total amount of hydrocarbon adsorbent is from 0.05 to 3.00 g in ^-3 , in particular from 0.10 to 2.00 g in ^-3 (for example, from 0.2 to 0.8 g in ^-3 ).

When the hydrocarbon adsorbent is a zeolite, preferably each zeolite is a medium pore zeolite (eg a zeolite with a maximum ring size of ten tetrahedral atoms) or a large pore zeolite (eg a zeolite with a maximum ring size of twelve tetrahedral atoms).

Examples of suitable zeolites or types of zeolite include faujasite (FAU), clinoptilolite, mordenite, silicalite (MFI), ferrierite, zeolite X (FAU), zeolite Y (FAU), ultra stable zeolite Y (FAU), zeolite AEI, zeolite ZSM-5, zeolite ZSM-12 (MTW), zeolite ZSM-20, zeolite ZSM-34, zeolite CHA, zeolite SSZ-13, zeolite SAPO-5 (AFI), offretite, beta zeolite or copper-containing zeolite CHA. The zeolite, if present, is preferably ZSM-5 (medium pore zeolite), beta zeolite (large pore zeolite), or Y zeolite (large pore zeolite). If a zeolite is present, a Y zeolite or a beta zeolite is preferred, with a beta zeolite being most preferred.

However, in accordance with the present invention, it is preferred that the oxidation catalyst (not including any protective layer against phosphorus and/or zinc, for an explanation of this detail, see later in this document) does not contain hydrocarbon adsorbents, in particular zeolites, since zeolites can be subjected to hydrothermal decomposition in the process of generating an exothermic effect, which makes their inclusion less desirable. The inclusion of hydrocarbon adsorbents in oxidation catalysts for high output vehicles is also less necessary because exhaust gas temperatures emitted from high output diesel engines rarely fall below temperatures at which hydrocarbon adsorption is desired to improve the overall hydrocarbon conversion cycle.

Porous oxide catalytic coating zone length

In embodiments containing only two porous oxide catalytic coating zones, such as those shown in FIG. 1, the length of the first zone of the porous oxide catalytic coating may be <50%, preferably 20 to 40% of the total length of the substrate.

However, in embodiments comprising three or four porous oxide catalytic coating zones, such as those shown in any of FIGS. 2-5 inclusive, the length of the first porous oxide coating zone can be from 15 to 35% of the total length of the substrate (L).

In embodiments comprising three or four porous oxide catalytic coating zones, such as those shown in any of FIGS. 2–5 inclusive, the length of the overlap region of the first and second layers (6, 7) of the porous oxide catalytic coating, i.e. the length of the second zone of the porous oxide catalytic coating shown in FIG. 2 and 4, or the length of the fourth zone of the porous oxide catalytic coating shown in FIG. 3 and 5 may be 10-40%, preferably 10-30% of the total length (L) of the substrate.

In embodiments comprising three or four porous oxide catalytic coating zones, such as those shown in any of FIGS. 2-5 inclusive, the length of the third zone of the porous oxide catalytic coating may be 10-40% of the total length (L) of the substrate, more preferably 15-35%, such as 20-30% of the total length (L) of the substrate.

In embodiments comprising four porous oxide catalytic coating zones, such as those shown in FIG. 3 and 5, the second porous oxide catalytic coating zone shown in FIG. 3 and 5 may be 1-40%, preferably 5-30% of the total length (L) of the substrate.

In a particularly preferred embodiment, the inlet porous oxide catalytic coating layer 6 is first applied to the substrate to a length of approximately 80% of L, and then the outlet porous oxide catalytic coating layer 7 is applied to the substrate to a length of approximately 50% of L, i. overlapping the porous oxide catalytic coating layer 6 by 30% of L. The length of the first porous oxide coating zone may be 15 to 35% of the total length (L) of the substrate.

Since the length of the substrate may vary, it is generally more useful to indicate the lengths of the first, second, and fourth zones of the porous oxide catalytic coating, if present, by their axial length relative to the overall axial length of the substrate, i. in percentages or parts. As such, the substrates used in the present invention have a length of 3-6 inches, inclusive, in particular 4-6 inches. Thus, it is possible to describe the length of the porous oxide coating layer or the length of the porous oxide coating zone as a percentage of the zone length x the total length of the substrate (L).

Uneven distribution of the alkaline earth metal component and/or the platinum group metal components in the porous oxide coating layer

This aspect is shown in FIG. 6 and 7 and briefly described in the description of the drawings presented above in this document.

In a first aspect of the invention, the first zone of the porous oxide catalytic coating may have a non-uniform distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate, as measured electronically. -probe microanalysis (EPMA), wherein the concentration of one or more platinum group metal components and/or the first alkaline earth metal components decreases perpendicular to the surface of the substrate as measured by EPMA.

It has been found that uneven vertical distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components can be achieved within a single layer. Thus, the multilayer advantages of achieving a non-uniform vertical distribution of these components across the catalyst beds can be achieved using a single layer or fewer layers.

In the oxidation catalyst composite of the invention, the first porous oxide catalytic coating zone may have an uneven distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate, optionally in a single layer, for example in a porous oxide catalytic coating layer, such as the first porous oxide catalytic coating layer (i.e., the catalyst layer does not have multiple layers).

Preferably, the porous oxide catalytic coating layer has a non-uniform distribution of one or more platinum group metal components and/or one or more alkaline earth metal components throughout its thickness (i.e., in a direction perpendicular to the surface of the substrate, representing the thickness of the catalyst layer), most preferably one or more platinum group metal components and one or more alkaline earth metal components.

Typically, the porous oxide catalytic coating layer has a first surface and a second surface. Typically, the first surface is parallel (eg, substantially parallel) to the second surface (ie, the plane containing the first surface is parallel to the plane containing the second surface). The first surface and the second surface are generally parallel to the surface of the substrate. Thus, the direction perpendicular to the surface of the substrate is also perpendicular to the first surface and/or the second surface.

The perpendicular distance between the first surface and the second surface is essentially the thickness of the porous oxide catalytic coating layer.

The first surface may be the exposed surface of the catalyst layer, or an additional layer (eg, a second layer) may be located or deposited on the first surface. The first surface is essentially on the top side (ie it is the top surface) of the catalyst layer. By openness is meant that the first surface is not completely covered or substantially not covered by another material, and, as a rule, the exhaust gas passing through the catalyst comes into contact with the first surface before coming into contact with the second surface.

The second surface is not an open surface of the porous oxide catalytic coating layer. Typically, the second surface is in direct contact with the surface of the substrate and/or the surface of the other layer. Thus, the second surface is essentially the underside (ie, the lower or lowest surface) of the porous oxide catalytic coating layer.

Preferably, the content of one or more platinum group metal components and/or one or more first alkaline earth metal components decreases in a direction perpendicular to the surface of the substrate (i.e., the amount of one or more platinum group metal components). group, and/or one or more first alkaline earth metal components decreases from the first surface to the second surface). The content of one or more platinum group metal components and/or one or more first alkaline earth metal components may decrease continuously or decrease discontinuously, preferably decreasing continuously in a direction perpendicular to the surface of the substrate. Thus, when, for example, the first porous oxide catalytic coating zone comprises one layer, which is a porous oxide catalytic coating layer, the content of one or more platinum group metal components and/or one or more first components representing is an alkaline earth metal, decreases from the exposed surface of the porous oxide catalytic coating layer to the surface of the substrate.

The porous oxide catalytic coating layer may have a linear or non-linear degree of reduction in the amount of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate (i.e. linear or non-linear rate of reduction of the amount of the first platinum group metal in the perpendicular direction from the first surface to the second surface).

Typically, at least 60% of the total amount of one or more platinum group metal components and/or one or more first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and a point or plane in the porous oxide catalytic coating layer that is half the distance between the first surface and the second surface (eg, 50% of the perpendicular distance between the first surface and the second surface). This plane is generally parallel to the first surface. The designation "at half the distance" in this context essentially refers to half the average distance between the first surface and the second surface. Preferably at least 70%, more preferably at least 75%, such as at least 80%, even more preferably at least 90% of the total amount of one or more platinum group metal components and/or one or more the first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and a point or plane in the porous oxide catalytic coating layer that is halfway between the first surface and the second surface.

Typically, at least 60% of the total amount of one or more platinum group metal components and/or one or more first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and a point or plane in the porous oxide catalytic coating layer located at 25% of the perpendicular distance from the first surface to the second surface. This plane is generally parallel to the first surface. Preferably at least 70%, more preferably at least 75%, such as at least 80%, even more preferably at least 90% of the total amount of one or more platinum group metal components and/or one or more the first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and a point or plane in the porous oxide catalytic coating layer located at 25% of the perpendicular distance from the first surface to the second surface.

At least 60% of the total amount of one or more platinum group metal components and/or one or more first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and the point or a plane in the porous oxide catalytic coating layer located at 10% of the perpendicular distance from the first surface to the second surface. This plane is generally parallel to the first surface. Preferably at least 70%, more preferably at least 75%, such as at least 80%, even more preferably at least 90% of the total amount of one or more platinum group metal components and/or one or more the first alkaline earth metal components (e.g., porous oxide catalytic coating layer) may be distributed between the first surface and a point or plane in the porous oxide catalytic coating layer located at 10% of the perpendicular distance from the first surface to the second surface.

The uneven distribution of the first platinum group metal in a direction perpendicular to the surface of the substrate may generally be an ordered distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components. In an alternative embodiment, the uneven distribution of the first platinum group metal in a direction perpendicular to the surface of the substrate may be a staggered distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components.

The porous oxide catalytic coating layer may have a uniform horizontal distribution or a non-uniform horizontal distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components.

Typically, the distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction parallel to the surface of the substrate (i.e., the longitudinal plane) and perpendicular to the central longitudinal axis of the substrate ( i.e. in a direction parallel to the inlet end surface and/or the outlet end surface of the substrate) is uniform or non-uniform. Preferably, the distribution of the first platinum group metal in a direction parallel to the surface of the substrate and perpendicular to the central longitudinal axis of the substrate is uniform.

As such, the distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction parallel to the surface of the substrate (i.e., longitudinal plane) and parallel to the central longitudinal axis of the substrate (m i.e. in a direction perpendicular to the inlet end surface and/or the outlet end surface of the substrate) may be uniform or non-uniform. Preferably, the distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction parallel to the substrate surface and parallel to the central longitudinal axis of the substrate is uniform.

Methods for obtaining a non-uniform distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in the first zone of a porous oxide catalytic coating in a direction perpendicular to the surface of the substrate are conventional thermal drying of dissolved salts of one or more platinum group metal components impregnated with a porous oxide coating containing one or more platinum group metals, and a first heat-resistant metal oxide substrate material, wherein one or more of the first components is an alkaline earth metal, is present in the porous oxide coating and/or as a dissolved salt in the impregnation medium along with a dissolved salt of one or more platinum group metal components. The first alkaline earth metal components are preferably present in a porous oxide coating on which one or more platinum group metal components are deposited. Impregnation is a common known technique described, for example, in Chapter 2.3 of Heck et al., Catalytic Air Pollution Control—Commeral Technology, Third Edition (2009), John Wiley & Sons, Inc. This reference chapter also discusses thermal drying and calcination. The inventors have found that an alternative drying method, freeze drying (see, for example, WO 2009/080155), which forms well-dispersed alkaline earth metal particles in a direction perpendicular to the surface of the substrate, provides less usable exothermic effects. Additional explanation can be found in the Obtaining Methods section later in this document.

The alkaline earth metal is preferably barium. When using alkaline earth metals other than barium, for example in the form of acetates, it has been found that alkaline earth metal salts other than barium are less mobile in the drying step and therefore do not generally form an uneven distribution, and this applies to such alkaline earth metal salts like strontium, calcium or magnesium. The applicant believes that the presence of a platinum group metal, in particular palladium, and barium on the upper surface of the porous oxide catalytic coating layer, for example, in the so-called "skin", is favorable for generating an exothermic effect, which is the main purpose of the composite oxidation catalyst of the present invention. Thus, in addition to the uneven distribution of the barium component in the direction perpendicular to the substrate surface, as measured by EPMA, with the concentration of the barium component decreasing in the perpendicular direction towards the substrate surface, the concentration of palladium also decreases in the perpendicular direction towards the substrate surface.

Protective layer against phosphorus and/or zinc

As explained in the introduction to the present description, lubricants for high performance vehicles have a relatively high content of additives containing zinc and/or phosphorus. As a result, catalysts in the exhaust systems of high-performance vehicles are exposed to relatively large amounts of zinc and/or phosphorus compounds during the lifetime of a vehicle. The inventors analyzed the oxidation catalyst, which was the first catalytic support located in the exhaust system downstream of a Euro 6 heavy duty diesel engine at the end of the vehicle's life (about 1 million kilometers), and found that In the oxidation catalyst, 1.0 to 1.5 weight percent phosphorus was present in the first quarter of the coated support, counted from the inlet end of the support.

In the present invention, the first zone of the porous oxide catalytic coating has the largest load of platinum group metals on the substrate, and it is located in the zone provided at the first end of the substrate corresponding to the inlet end in use. According to the invention, the highest load of platinum group metals in the form of a platinum-rich combination of platinum and palladium is a key characteristic of the composite oxidation catalyst for generating an exothermic effect using increased amounts of hydrocarbons present in the exhaust gas. Thus, the presence of zinc and/or phosphorus catalyst poisoning agents in the exhaust gas entering the upstream end of the composite oxidation catalyst can have a disproportionate effect in reducing catalyst activity when generating an exothermic effect using hydrocarbons due to the additional need for hydrocarbons to achieve the desired exothermic temperature, as a result of which the fuel economy of the vehicle is indirectly reduced; and/or due to an increase in the ignition temperature of hydrocarbons, i. e. the temperature at which the catalyst activates the initiation of the oxidation of hydrocarbons and thus the generation of an exothermic effect, as compared to an oxidation catalyst uniformly coated with the same porous oxide coating composition (see also Examples 4, 5 and 6 below herein). Thus, hydrocarbons introduced into the exhaust gas at relatively lower temperatures, at which some exotherm would normally be expected, may result in reduced exotherm and increased hydrocarbon slippage and hence higher hydrocarbon emissions and/or hydrocarbon pollution. downstream exhaust system components or processes and/or internal diagnostic (OBD) failure mode.

The inventors studied methods for reducing or preventing the effects of phosphorus and/or zinc poisoning in a composite oxidation catalyst and found that by applying a porous oxide coating layer as an outer layer to the first zone of the porous oxide catalytic coating with sufficient load (correlating with layer thickness porous oxide coating), and optionally the porous oxide coating contains a particulate metal oxide with a sufficient average pore diameter, and/or the resulting porous oxide coating has a sufficient average pore size between particles, contact of phosphorus and/or zinc compounds with located below the first zone of coating of porous oxide, and during the operation of the catalyst, a higher proportion of fresh catalyst activity is maintained than in a catalyst without the use of such an additional feature, while access of the exhaust gas in terms of mass exchange with the located oh below the first porous oxide coating zone.

Accordingly, in a preferred construction, the composite oxidation catalyst according to the first aspect of the invention comprises an outer porous oxide coating layer extending axially from the first end of the support to protect at least a portion of the underlying first zone of the porous oxide coating from phosphorus poisoning and/ or zinc in service, wherein the outer porous oxide coating layer has a metal oxide powder load of ≥0.8 g/in ³ .

Applicant's studies have shown that the depth of the outer layer of the porous oxide coating appears to be important to achieve the desired function of the protective layer against phosphorus and/or zinc compounds, since it was found that the relatively low load of the outer layer of the porous oxide coating of 0.5 g /in ³ is not as effective as loading with an outer layer of porous oxide coating of 1.0 g/in ³ (see examples 4, 5 and 6 below in this document).

The outer layer of the porous oxide coating may consist essentially of powdered metal oxide, and the outer layer of the porous oxide coating may contain certain binders or additives to aid processing, such as powder flow modifiers, rheology modifiers of the porous oxide coating, etc. That is, although catalytic components such as barium or one or more platinum group metals may seep or migrate into the outer layer of the porous oxide coating of their underlying layer during the manufacture of the composite oxidation catalyst, the metal oxide particles are applied as a coating, such as a porous oxide coating. , which does not include such metals and is not intended to include such metals in the outer layer of the porous oxide coating. In this context, the term "substantially" used herein above should encompass the end product in which any such metals inadvertently migrate into the outer porous oxide coating layer.

Typically, the outer layer of the porous oxide coating has a powder metal oxide load of 0.8 to 3.5 g/in ^-3 , preferably 0.9 to 2.5 g/in ^-3 , even more preferably 1.0 up to 2.0 g/in ^-3 , for example from 1.1 to 1.75 g/in ^-3 .

Preferably, the outer porous oxide coating layer is applied directly to the porous oxide coating of the first zone of the porous oxide catalytic coating. However, it is within the scope of the present invention to include one or more porous oxide coating layers between the first porous oxide catalytic coating zone and an outer porous oxide coating layer of a preferred configuration.

It should be understood that the application of the protective layer element is essentially applicable to all embodiments of the present invention, and therefore can be easily combined with each and every embodiment of the present invention, as specifically shown in the embodiments described in FIG. 1–5 inclusive, and as shown by the optional dashed line G.

The outer porous oxide coating layer may have one or more of the following additional optional features:

(a) the metal oxide powder in the outer layer of the porous oxide coating has an average pore diameter of ≥10 nm and/or the outer layer of the porous oxide coating has an average pore diameter between particles of ≥10 nm;

(b) the metal oxide powder in the outer layer of the porous oxide coating is selected from the group consisting of alumina, silica, titanium oxide, zirconium oxide, cerium oxide, and a mixed or composite oxide of any two or more of these, or an aluminosilicate zeolite. Preferably, the metal oxide powder is silica-doped alumina or alumina having an average pore diameter of ≧15 nm;

(c) the specific surface area of the metal oxide powder in the outer layer of the porous oxide coating is >100 m ² /g;

(d) the outer porous oxide coating layer extends axially up to 150% of the axial length of the underlying first porous oxide catalytic coating layer from the first end of the substrate, to thereby protect it from phosphorus and/or zinc poisoning during operation in the exhaust system of a heavy duty diesel engine, preferably >50% of the axial length of the underlying first porous oxide catalytic coating zone, for example >60%, >70%, >80%, >90%, or >100%, or up to 120% of its axial length; and

(e) the metal oxide powder in the outer layer of the porous oxide coating is coated with a platinum group metal, which is platinum or a combination of platinum and palladium at a mass ratio of Pt : Pd ≥ 1 : 1, and optionally loading with platinum group metals in the outer layer of the coating from porous oxide is 1–35 g ft ^-3 . The platinum group metal is deliberately incorporated into the outer layer of the porous oxide coating.

The metal oxide powder may have one or both of an average pore diameter and an interparticle pore diameter of ≧10 nm. Preferably, the average pore diameter or interparticle pore diameter is ≥12 nm or ≥15 nm. The Applicant has found that certain parameters of the metal oxide powder may undesirably reduce the oxidative activity of hydrocarbons in the underlying first zone of the porous oxide coating. Thus, when Applicant tested colloidal silica (Ludox™) as a possible metal oxide powder for use in the outer porous oxide coating layer, it was found that the porous oxide coating layer was insufficiently porous and sufficiently permeable to support the oxidative function of the underlying first layer. porous oxide catalytic coating. Thus, the oxidation of hydrocarbons in the composite oxidation catalyst including colloidal silica as metal oxide powder was limited in terms of gas mass transfer. Although a lower colloidal silica load may provide improved mass transfer, it is expected that the protective effect of the outer layer of the porous oxide coating will be insufficient (see load limitation of the porous oxide coating ≥0.8 g/in ³ described above in this document). Thus, in order to better maintain the main function of hydrocarbon oxidation of the composite oxidation catalyst, the metal oxide powder has an average pore diameter of ≥10 nm and/or the outer layer of the porous oxide coating has an average interparticle pore diameter of ≥10 nm.

In embodiments that use a porous oxide outer coating layer without a deposited platinum group metal, the present inventors have found that some metal oxide powders having a relatively low average pore diameter, such as cerium oxide powder having a fresh average pore diameter of 8 nm can be effective in the present invention. Preferably, however, the metal oxide powder in the outer porous oxide coating layer has an average pore diameter of ≥10 nm and/or the outer porous oxide coating layer has an average particle-to-particle pore diameter of ≥10 nm, preferably an average pore diameter of ≥10 nm. Thus, a powdered metal oxide, such as cerium oxide material, which initially has a low average pore diameter, can find use in the present invention by appropriately selecting the particle size distribution (see also below herein) such that the average pore diameter between particles in the porous oxide coating layer was ≥10 nm.

The average pore diameter between the particles of the outer layer of the porous oxide coating can be determined using mercury porosimetry.

The average pore diameter of the metal oxide powder can be determined from N ₂ adsorption-desorption isotherms using the Barrett-Joyner-Halend (BJH) technique.

If the metal oxide powder has a bimodal pore diameter, then the requirement is met that at least one of the two modes has a particle diameter of ≥10 nm. For the avoidance of doubt, it should be clarified that the preferred silicon dioxide doped refractory metal oxide powder meets at least the general definition given in this section.

Aluminosilicate zeolites essentially do not meet the requirement that the average pore diameter be ≥10 nm. The characteristic that the pore diameter between the particles is ≥10 nm can be obtained by appropriate selection of the particle size, i.e. particle size distribution. As explained above with respect to colloidal silica in which the porous oxide coating particles are too small, the pores between the particles are too small to support the mass exchange of the exhaust gas with the underlying first porous oxide catalytic coating layer. By appropriate choice of particle size, pores between particles of a suitable size can be obtained to meet the preferred condition of pore diameter between particles ≧10 nm.

For example, the D90 value for powdered metal oxide particles may be <100 µm. The metal oxide powder particles may preferably have a D90 of <75 µm, eg <50 µm (eg <30 µm), and more preferably <20 µm, eg <15 µm. When the refractory oxide has a lower D90 value, better packing and adhesion can be achieved.

As known to those skilled in the art, D90 is a particle size value such that 90% of the particles in the distribution are smaller than this value. For the avoidance of doubt, D90 measurements can be made using laser diffraction particle size analysis on a Malvern Mastersizer 2000™ analyzer, which is a volume-based technique (i.e. D90 can also be called D _V 90 (or D(v,0, 90)) and uses the mathematical model of Mie theory to determine the particle size distribution.

Typically, the D90 value for powdered metal oxide particles is <0.1 µm. Preferably, the D90 value for the metal oxide powder is >.0 µm, eg >5.0 µm.

Powdered metal oxides that meet the required conditions for use in the protective layer of the outer coating of porous oxide in accordance with the preferred configuration and find use in the present invention include alumina, silicon dioxide, titanium oxide, zirconium oxide, cerium oxide and mixed or composite oxide any two or more of these, such as silica-doped titania, cerium-zirconium mixed oxide, the preferred silica-doped alumina, or aluminosilicate zeolite. For example, the metal oxide powder may be selected from the group consisting of alumina, cerium oxide, silica-doped alumina, titanium oxide-aluminum oxide, zirconium oxide-alumina, cerium oxide-alumina, cerium oxide-zirconium oxide aluminium, silicon dioxide-titanium oxide, silicon dioxide-zirconium oxide, zirconium oxide-titanium oxide, cerium oxide-zirconium oxide and aluminum oxide-magnesium oxide. Preferably, the metal oxide powder is selected from the group consisting of alumina, silica-doped alumina, titania-alumina, zirconia-alumina, silica-titania, silica-zirconia, zirconia-titania and oxide aluminum-magnesium oxide.

The metal oxide powder may optionally be doped (eg with a dopant). The dopant may be selected from the group consisting of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), and their oxide. By incorporating a dopant, the metal oxide powder can be thermally stabilized. It should be understood that any reference to the term "doped" in this context refers to a material in which the main crystal lattice or the crystal lattice of the basic substance of the metal oxide powder is doped with a substituent or doped in between with a dopant. In some embodiments, small amounts of dopant may be present on the surface of the metal oxide powder. However, most of the dopant will essentially be present in the bulk of the metal oxide powder.

When doping the metal oxide powder, the total amount of the dopant is 0.5 to 15 wt%, preferably 1 to 10 wt% (eg about 5 wt%), based on the weight of the metal oxide powder. The preferred metal oxide powder is a refractory silica-doped alumina metal oxide that can meet the requirements for an average pore diameter of ≥10 nm and can also have a specific surface area of ≥ about 120 m ² /g (see below in this document ).

In embodiments where the metal oxide powder contains an aluminosilicate zeolite, examples of suitable zeolites or zeolite frameworks include faujasite, clinoptilolite, mordenite, silicalite, ferrierite, zeolite X, zeolite Y, ultrastable zeolite Y, zeolite AEI, zeolite ZSM-5, zeolite ZSM -12, ZSM-20 zeolite, ZSM-34 zeolite, CHA zeolite, SSZ-13 zeolite, offretite, beta zeolite or CHA copper zeolite. The zeolite is preferably ZSM-5, beta zeolite, or Y zeolite. The aluminosilicate zeolite may include one or more base metals, such as at least one of copper, iron, or manganese. For example, if the aluminosilicate zeolite has a framework type code CHA, the CHA may contain a copper promoter. In an alternative embodiment, the aluminosilicate zeolite may be intentionally free of base metals.

The powdered metal oxide may be a refractory metal oxide, a term which, as defined herein, excludes aluminosilicate zeolites.

A particularly preferred metal oxide powder for use in the present invention is a refractory metal oxide - doped with silica alumina at the total amount of doped silica described above herein, free of intentionally introduced noble metal, including a platinum group metal. In addition, alumina with an average pore size of ≥15 nm is preferred. Such materials are referred to herein as "wide-pore aluminas" and are known, for example, from EP1077769 A1.

It is believed that the specific surface area of the metal oxide powder is also important, since the greater the specific surface area of the metal oxide powder component, the greater the expected adsorption capacity of the outer layer of the porous oxide coating, for example, vitreous zinc phosphate, derived from lubricant additives.

The metal oxide powder particles for use in the outer layer of the porous oxide coating in the fresh composite oxidation catalyst according to the invention have a mean specific surface area (SSA) ≥ about 100 m ² /g (> about 100 m ² /g), preferably ≥ about 120 m ² /g (> about 120 m ² /g), for example ≥ about 150 m ² /g (> about 150 m ² /g), ≥ about 180 m ² /g (> about 180 m ² /g) or ≥ about 200 m ² /g (> about 200 m ² /g). Typically, aluminosilicate zeolites have an SSA ≥ about 200 m ² /g.

The average specific surface area (SSA) of the refractory oxide particles can be determined from the physical sorption of nitrogen at -196° C. using a volumetric method. The average SSA is determined using the BET equation for the adsorption isotherm.

In preferred embodiments, the metal oxide powder in the outer layer of the porous oxide coating is coated with a platinum group metal that is platinum or a combination of platinum and palladium at a weight ratio of Pt : Pd ≥ 1 : 1. It should be understood that the weight ratio of Pt : Pd 1 : 0, i.e. using only Pt, is in the range "≥1 : 1".

Preferably, the load of platinum group metals in the outer layer of the porous oxide coating is from 1 to 35 g/ft ^-3 , preferably from 2.5 to 25 g/ft ^-3 , for example from 5 to 17.5 g/ft ^-3 .

Adding Manganese to the Porous Oxide Catalyst Exhaust Layer to Improve NO ₂ Control and Exothermic Characteristics

During research into the development of the four-zone composite oxidation catalyst shown in FIG. 5, Applicant has found that manganese added to the third porous oxide catalytic coating zone formed at its second end by the second (i.e., outlet) end of the substrate as part of the second porous oxide catalytic coating layer (7) applied from the second ( outlet) end of the substrate, may favorably promote the generation of an exothermic effect and/or prevent the quenching of the exothermic reaction during regeneration of the active filter, increase the activity of the downstream SCR catalyst to reduce nitrogen oxides (NO _x ) to N ₂ and/or improve injection control a nitrogenous reducing agent for use in the downstream SCR catalyst. These observations can be applied equally to, inter alia, two-, three- and four-zone composite oxidation catalysts in accordance with the invention.

With respect to enhancing the activity of a downstream SCR catalyst for reducing NO _x to N ₂ as described above herein, it is known that in an exhaust gas containing both nitrogen monoxide and nitrogen dioxide, SCR catalysis occurs through a combination of reactions SCR, including reactions (1)–(3), each of which reduces NO _x to elemental nitrogen (N ₂ ).

The corresponding undesirable non-selective side reaction corresponds to reaction (4):

2NH ₃ + 2NO ₂ → N ₂ O + 3H ₂ O + N ₂ (4)

In practice, reactions (1) to (3) inclusive occur simultaneously, with the dominant reaction favoring, inter alia, according to the reaction kinetics and the relative concentrations of the reactants. From a kinetic point of view, reaction (2) is relatively slow compared to reaction (1), and reaction (3) is the fastest. Thus, according to these chemical properties, SCR catalysis works most efficiently if the NO ₂ /NO _x ratio in the exhaust gas entering the downstream SCR catalyst is approximately 0.5, i.e. ratio 1 : 1 NO : NO ₂ in accordance with reaction (3).

Applicant's investigators have found that by incorporating manganese into the third zone of the porous oxide catalytic coating of the composite oxidation catalyst shown in FIG. 5, the composition of the second porous oxide catalytic coating layer (7) can suppress the peak passive oxidative activity of NO, i. e. the oxidative activity of NO occurring between active exothermic/regeneration events. The "peak passive oxidative activity of NO" is illustrated by the values in the column "fresh, NO ₂ /NO _x at 300°C (%)" in tables 7 and 8.

By suppressing peak oxidative activity using manganese, Applicant's researchers have found that the NO ₂ /NO _x ratio in a "fresh" and "aged" composite oxidation catalyst can be varied over a significant portion of a vehicle's life to a more stable value between 0.55 and 0. .45, i.e. "favorable window" for carrying out the reaction (3) on the downstream SCR catalyst instead of the kinetically slower and less efficient reaction (2) NO _x reduction. If the activity of the fresh catalyst in terms of passive oxidation of NO is too high, then the peak content of NO ₂ /NO _x in the exhaust gas can rise to a value in excess of 0.65, which not only shifts the composition of the exhaust gas from the preferred NO ratio for promoting reaction (3): NO ₂ 1 : 1 in the downstream SCR catalyst, but also, secondly, stimulates the slowest reaction (2). Moreover, an excess of NO ₂ can lead to undesirable formation of N ₂ O in accordance with reaction (4).

In terms of improving the control of nitrogenous reductant injection for use in the downstream SCR catalyst, Applicant's investigators also found that if the third zone contained manganese, the difference (delta) between the fresh and aged composite catalyst in terms of NO passive oxidative activity was generally reduced. (see the results presented in tables 7 and 8). Thus, the resulting NO ₂ /NO _x ratio in the exhaust gas downstream of the composite oxidation catalyst was more predictable over the life of the vehicle exhaust system, since the catalyst is fresh at the beginning and ages with use. In practice, this observation is important because the catalytic SCR reaction essentially requires the provision of a nitrogenous reducing agent (see reactions (1)-(3) above in this document). Typically, this nitrogenous reducing agent is ammonia (NH ₃ ), which is present in the vehicle in the form of a precursor, urea, for delivery into the exhaust gas stream by an injector. On contact with hot exhaust gas, urea decomposes into ammonia and water vapour. It can be seen from reactions (1)–(3) that, depending on which reaction is dominant at any particular point in time, slightly different amounts of the nitrogenous reducing agent, ammonia, are required to ensure the most efficient reduction of total NO _x if NH ₃ slip is to be avoided. .

An additional level of complexity is that the ability of the oxidation catalyst to oxidize NO to NO ₂ decreases over time; this is the so-called "aging". This loss of activity over time leads to increased complexity in the design of control systems for the delivery of a nitrogenous reducing agent, since the gradual loss of activity in system software algorithms must be compensated for. However, if the difference between NO oxidizing activity of fresh and aged catalyst is reduced, in addition to suppressing increased NO oxidizing activity, with "focusing" NO ₂ /NO _x at about 0.5, as described above in this document, diesel vehicle manufacturers heavy-duty engine, it will be easier to maintain system software control of nitrous reductant injection over the life of the vehicle.

Thirdly, and very unexpectedly, Applicant's investigators have found, as shown in Example 9 below herein, that the incorporation of manganese into the third porous oxide coating zone/second porous oxide coating layer can have a favorable exothermic and/or exotherm promoting effect. to prevent exotherm damping during active filter regeneration. Due to this observation, it is possible to maintain the functionality of the composite oxidation catalyst using an inexpensive base metal, i.e. manganese, instead of the much more expensive platinum group metals.

During the post-treatment step in the exhaust system, manganese can be affected by sulfur poisoning. Palladium is also known to be poisoned. For this reason, it may be preferable to avoid including palladium in addition to manganese in the porous oxide coating layer and/or zone containing the manganese catalyst. However, as mentioned above herein, palladium at a relatively low content can increase the stability of the platinum component in the zone. In this regard, it is preferable that the manganese-containing layer and/or zone of the porous oxide catalytic coating have a mass ratio of Pt : Pd with a high content of platinum, for example ≥10 : 1, or, otherwise, one or more platinum group metals in containing The manganese layer and/or the catalytic porous oxide coating zone may consist essentially of or consist of platinum (ie have a Pt : Pd weight ratio of 1 : 0).

To take advantage of the described technical effects of manganese incorporation, the load of platinum group metals in the layer and/or zone of the catalytic coating of porous oxide containing manganese is preferably ≥2 g ft ^-3 , preferably from 5 to 15 g ft ^-3 , for example from 7 to 13 g ft ^-3 .

In addition, the Applicant has found that the technical effect of the manganese-reduced "delta" between the oxidation of NO to NO ₂ with fresh and aged catalyst can be enhanced by proper selection of a heat-resistant metal oxide support material in the porous oxide catalytic coating zone formed on its second the end of the second end of the substrate, for example in the third zone of the porous oxide catalytic coating, and/or in the second layer of the porous oxide catalytic coating.

In this regard, the Applicant has observed the advantage of heteroatom-doped alumina substrate materials, preferably the heteroatom being silicon and/or manganese; or is a mixed oxide of magnesium-aluminum. The manganese may be present as a heteroatom per se and/or it may be incorporated as a soluble salt in combination with a refractory porous metal oxide support material such as mixed magnesium-alumina or a silica-doped alumina support material, e.g. , as manganese nitrate, followed by precipitation onto the substrate material using a reducing agent such as citric acid, tetrabutylammonium hydroxide, formic acid, ascorbic acid, etc. The refractory metal oxide substrate containing doped manganese can in turn be impregnated with additional manganese.

Accordingly, the refractory metal oxide substrate material in the manganese containing zone or layer may comprise silica doped alumina, manganese doped alumina, both silica and manganese doped alumina, magnesium-aluminum mixed oxide, or "preformed" manganese-doped mixed magnesium-aluminum oxide. The impregnating manganese component can be applied to a heat-resistant metal oxide substrate material.

The mixed magnesium-alumina may have a pre-calcination magnesium content of less than 15 wt.% based on Mg, for example 0.1 to 12 wt.% or 2.0 to 10 wt.%. The calcined substrate material containing mixed alumina-magnesium oxide may be magnesium-deficient, i.e. non-stoichiometric, spinel. Most preferably, the manganese-containing refractory metal oxide substrate material is a manganese-doped "pre-produced" mixed magnesium-aluminum oxide. The amount of manganese doping additive in manganese-doped alumina-magnesium oxide can be 1–15 wt %. % based on MnO ₂ . Example 8 shows that samples containing manganese-doped magnesium alumina exhibited an unexpected improvement in exotherm generation at lower temperature, as evidenced by the "continuous exotherm" test, as well as a reduction in "delta" between fresh and aged catalysts for the ratio _NO2 / _NOx .

Substrate

Supports for containing the components of the porous oxide catalytic coating layer and the porous oxide catalytic coating zone of the composite oxidation catalyst of the present invention are well known in the art. In general, the substrate is made of a ceramic material or a metal material.

Preferably, the substrate is made or consists of cordierite (SiO ₂ -AI ₂ O ₃ -MgO), silicon carbide (SiC), aluminum titanate (AT), Fe-Cr-AI alloy, Ni-Cr-AI alloy or stainless steel.

As a rule, the substrate is a monolith, i.e. monolithic substrate. Preferably, the monolith is a flow-through honeycomb monolith substrate or a filter substrate monolith, most preferably a flow-through honeycomb substrate monolith.

The composite oxidation catalyst is preferably for use as a diesel oxidation catalyst (DOC) or a catalyzed diesel particulate filter (CSF). In practice, the catalyst compositions used in DOC and CSF are similar. However, in general, the main difference between DOC and CSF lies in the support on which the catalyst composition is applied and the amount of platinum group metal in the coating.

A flow monolith is typically a honeycomb monolith (eg, a metal or ceramic honeycomb monolith) through which a plurality of channels pass, the channels being open at both ends. When the support is a flow monolith, the composite oxidation catalyst of the invention is generally referred to as a diesel oxidation catalyst (DOC) or for use as a diesel oxidation catalyst (DOC).

When the monolith is a filter monolith, the filter monolith is preferably a flow wall filter. In a flow wall filter, each inlet is in turn separated from the outlet by a porous structure wall and vice versa. The inlet and outlet are preferably honeycomb-shaped. In a honeycomb structure, passages vertically and laterally adjacent to the inlet are preferably plugged at the upstream end and vice versa (i.e., passages vertically and laterally adjacent to the outlet are plugged at the downstream end). move end). When viewed from both ends, the alternately closed and open ends of the channels should look like a checkerboard. When the substrate is a filter monolith, the oxidation catalyst of the invention is typically a catalyzed diesel particulate filter (CSF) or is intended for use as a catalyzed diesel particulate filter (CSF).

In principle, the substrate may be of any shape or size. However, the shape and size of the support is generally chosen to optimize the effect of the catalytically active materials in the catalyst on the exhaust gas. The support may, for example, be tubular, fibrous or particulate. Examples of suitable substrates include a monolithic cordierite honeycomb substrate, a monolithic SiC honeycomb substrate, a layered fiber or woven substrate, a foam substrate, a cross-flow substrate, a metal wire mesh substrate, a metal porous body substrate, and a ceramic particle substrate.

high power motors

For the avoidance of doubt, it should be clarified that for high power motors in accordance with the third aspect of the invention, any of the definitions presented above in the "Background of the Invention" section can be used. Thus, for example, if the patent application is for Japan, the claims may include the restrictions required by Japanese heavy duty diesel vehicle emission standards. The same applies to the legislation of Europe, the USA, etc. For the avoidance of further doubt, it should be clarified that high power engines for use in the present invention do not provide lean/rich cycle control suitable for normal operation or desulfation of the LNT catalyst. In preferred designs, the exhaust system according to the invention does not include LNT.

The high power compression ignition engine according to the third aspect of the present invention is preferably a diesel engine, optionally a compressed natural gas (CNG) engine. The heavy duty diesel engine may be a homogeneous mixture compression ignition (HCCI) engine, a premixed compression compression ignition (PCCI) engine, or a low temperature combustion (LTC) engine. Preferably, the diesel engine is a conventional (ie conventional) diesel engine.

How to get

Methods for preparing the oxidation catalyst of the invention are known in the art. See, for example, our publications WO 99/47260, WO 2007/077462 and WO 2011/080525. Likewise, the conditions for drying and calcining a porous oxide coating are also well known.

As mentioned above, in an alternative embodiment according to the first aspect of the invention, the oxidation catalyst may comprise three or more porous oxide catalytic coating zones, preferably four porous oxide catalytic coating zones.

The method for producing such a catalyst corresponds to the sixth aspect of the invention, wherein in step (a) the porous oxide catalytic coating layer is a first porous oxide catalytic coating layer that extends from the first end of the substrate to a length less than the total length of the substrate, the method further includes step (a') before step (a) or after step (a), but in any case before step (b), consisting in applying a second layer of porous oxide catalytic coating on the substrate from the second end of the substrate to a length less than the total length of the substrate so that the first porous oxide catalytic coating layer partially overlaps the second porous oxide catalytic coating layer or the second porous oxide catalytic coating layer partially overlaps the first porous oxide catalytic coating layer, wherein the second porous oxide catalytic coating layer comprises a substrate material of heat-resistant oxide me tallium and one or more platinum group metal components.

In this regard, it is preferable that the first porous oxide catalytic coating layer can extend from the first end of the substrate, and the second porous oxide catalytic coating layer extends from the second end of the substrate, the second porous oxide catalytic coating layer partially overlapping the first porous oxide catalytic coating layer. porous oxide.

In embodiments, this preferred method may provide configurations such as those shown in FIG. 4 and 5, i.e. depending on the axial length of the region of application of the second porous oxide catalytic coating in step (a'), and thus on the axial length of the overlap region of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer, wherein the first catalytic zone The porous oxide coating comprises one layer of a first porous oxide catalytic coating deposited on the surface of the substrate. Depending on the axial length of the application area L ₁ in step (b), the second or fourth porous oxide catalytic coating zone may include an overlap region of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer. The third porous oxide catalytic coating zone comprises one porous oxide coating layer deposited on the substrate surface, formed at its second end by the second end of the substrate, and at its first end by the second end of the first porous oxide catalytic coating layer, i. at the point at which the second layer extending from the second end of the substrate towards the first end of the substrate begins to overlap the first porous oxide catalytic coating layer. Typically, the first end of the third porous oxide catalytic coating zone is the second end of the second or fourth porous oxide catalytic coating zone.

Such an arrangement is advantageous because the exhaust gas entering the oxidation catalyst of the invention at the first inlet end of the support substantially contacts the porous oxide catalytic coating overlap region zone in front of the third porous oxide catalytic coating zone. The zone of overlap of the catalytic porous oxide coatings (depending on the embodiment, either the second or the fourth zone of the catalytic porous oxide coating) acts as a "stabilizer" for the first zone of the catalytic porous oxide coating. The overlap region zone of the porous oxide catalytic coatings acts as a "stabilizer" in that it performs some or all of the oxidation reactions of the first zone of the porous oxide catalytic coating, but the overlap region zone of the catalytic porous oxide coatings may have a higher firing temperature for HC. and/or CO than the first zone of the porous oxide catalytic coating.

It should be understood that in the sixth aspect of the invention, because the first zone of the porous oxide catalytic coating is obtained in step (b) by impregnating the porous oxide catalytic coating applied in step (a), the refractory metal oxide support material in the first zone of the porous oxide catalytic coating may be the same heat-resistant metal oxide substrate material used in the porous oxide catalytic coating, for example, in the first porous oxide catalytic coating layer deposited in step (a).

A first zone of a porous oxide catalytic coating having a non-uniform distribution of one or more platinum group metal components, and optionally one or more first alkaline earth metal components, in a direction perpendicular to the surface of the substrate, as determined by electron probe microanalysis (EPMA) ), wherein the concentration of one or more platinum group metal components, and optionally the first alkaline earth metal components, decreases in a direction perpendicular to the surface of the substrate according to EPMA, can generally be obtained by a method in which one or more of the platinum group metal components and/or one or more of the first alkaline earth metal components do not rapidly attach to the refractory metal oxide substrate material and remain movable within the porous oxide coating when drying. A porous oxide coating containing one or more platinum group metal components may be applied to the substrate followed by a thermal drying step and a calcination step using conditions to move one or more platinum group metal components and optionally one or more of the first alkaline earth metal components within the coating until they are fixed in place. Such conditions are known in the art, particularly since prior art conditions are typically chosen to quickly fix the components of the coating (ie, the porous oxide coating) to prevent them from moving within the coating. Thus, if there is awareness of the conditions for fast fixation and prevention of migration of platinum group metal salts within a drying porous oxide coating, this provides an idea of the conditions that allow such migration.

The transport of solutes to or from a wet surface during evaporation is an effect known in other technical fields. The transfer of the first platinum group metal (i.e. platinum group metal salt and/or alkaline earth metal salt) in the wet coating can be represented by the Richards equation:

where:

t is time (eg, time to substantial or complete evaporation of the solvent (ie water)); and represents the content of the solvent (ie water), as a rule, in the coating; K - hydraulic conductivity; z - height; and w - head height. The hydraulic conductivity can be approximated by the hydraulic conductivity of the first substrate material and/or any other substrate material present.

A method for producing a porous oxide catalytic coating zone having an uneven distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the substrate surface includes:

(a) providing an aqueous slurry comprising a refractory metal oxide support material, one or more platinum group metal components, and optionally one or more alkaline earth metal components;

(b) applying an aqueous suspension to a substrate to form a porous oxide coating; and

(c) drying and calcining the porous oxide coating, the drying conditions allowing at least one or more platinum group metal components and optionally one or more alkaline earth metal components to flow to or from the substrate, such that to obtain uneven distribution of one or more platinum group metals and optionally one or more alkaline earth metal components in a direction perpendicular to the surface of the substrate.

The porous oxide coating may comprise two or more platinum group metal components, wherein the first platinum group metal component may be referred to as the first platinum group metal component and the second platinum group metal component may be referred to as the second component, which is a platinum group metal.

Generally, at least one of the heat-resistant metal oxide substrate material, the first platinum group metal component, and the second platinum group metal component is insoluble. However, it should be understood that the slurry may be a solution, for example, when one or more of the refractory metal oxide substrate material precursors, the first platinum group metal component, and the second platinum group metal component are soluble (i.e., e. dissolved).

Generally, the refractory metal oxide substrate material precursor is a compound that undergoes transformation into a refractory metal oxide substrate material after drying and/or calcining the coating. Such refractory metal oxide substrate material precursors are well known in the art and include, for example, boehmite as a gamma alumina precursor.

Typically, the first platinum group metal component is a salt of the first platinum group metal or is the first platinum group metal (ie, it is the first platinum group metal as such). Preferably, the first platinum group metal component is a salt of the first platinum group metal. The salt of the first platinum group metal may be a nitrate salt of the first platinum group metal, an acetate salt of the first platinum group metal, or a carboxylate (eg, citrate) salt of the first platinum group metal.

The second platinum group metal component is typically a salt of a second platinum group metal or a second platinum group metal (ie, the second platinum group metal itself). Preferably, the second platinum group metal component is a salt of the second platinum group metal. The second platinum group metal salt may be a nitrate salt of the second platinum group metal, an acetate salt of the second platinum group metal, or a carboxylate (eg, citrate) salt of the second platinum group metal.

When two or more different platinum group metals are used (for example, when the first platinum group metal is different from the second platinum group metal), there may be a difference in mobility between the first platinum group metal component and the second platinum group metal component, which is due to the difference in the metals present, resulting in a different distribution profile of each platinum group metal compared to the other (or each) platinum group metal in the porous oxide coating layer (see FIG. 6). The same applies to the differential mobility of the alkaline earth metal relative to one or more platinum group metal components present in the porous oxide catalytic coating layer. It is possible to vary the mobility as well as the preferred perpendicular flow direction in the porous oxide catalytic coating layer of the platinum group metal components by selecting the appropriate anion when the platinum group metal component is a salt of the platinum group metal. The platinum group metal components may also interact differently with the heat resistant metal oxide substrate material and may be selected on this basis. Similarly, the mobility of the alkaline earth metal components within the porous oxide catalytic coating layer can be varied by appropriate selection of their soluble salt.

Preferably, the counter anion of the salt of the first platinum group metal is different from the counter anion of the salt of the second platinum group metal. For example, the first platinum group metal component may be palladium nitrate and the second platinum group metal component may be platinum carboxylate. The nitrate anion is different from the carboxylate anion.

The mobility of at least one of the platinum group metal components can be altered by applying it to a support material (i.e., pre-fixing the platinum group metal component) prior to mixing with the other platinum group metal component. For example, the pre-fixed first platinum group metal/first refractory metal oxide substrate material may be mixed with a second refractory metal oxide substrate material and an aqueous salt of the second platinum group metal and optionally an aqueous salt of one or more alkaline earth metals.

One method by which the first platinum group metal component can be applied to the first refractory metal oxide substrate material is by: (i) mixing the first refractory metal oxide substrate material and the first platinum metal oxide component. groups, in solution, preferably to impregnate or fill the pores of the final first heat-resistant metal oxide substrate material; and (ii) drying and/or calcining the aqueous solution to form a first platinum group metal component (eg, a first platinum group metal) supported on a first heat resistant metal oxide substrate material. Step (i) may be followed by step (i)(a) adding a reducing agent to reduce the first platinum group metal component, preferably to impregnate or fill the pores of the first support material. In steps (i) and/or (i)(a), it is preferred that the first platinum group metal component be the only platinum group metal component present.

Thus, step (a) of the method described above may be step (a) of obtaining an aqueous slurry containing a second platinum group metal component and a first platinum group metal component deposited on the first substrate material precursor.

With respect to step (b), methods for applying suspensions or porous oxide coatings to a substrate are well known in the art (see, for example, Applicant's WO 99/47260).

In one embodiment, step (c) comprises drying the coating under drying conditions that allow at least the first platinum group metal component and the second platinum group metal component to move at different speeds from each other in a direction perpendicular to plane representing the surface of the substrate. In another embodiment, step (c) comprises drying the coating under drying conditions that allow only the first platinum group metal component to flow to or from the substrate.

Step (c) determines the point at which the platinum group metal components are generally fixed to a heat-resistant metal oxide substrate or substrate material. The drying conditions used will depend on the nature of the materials (e.g., platinum group metal components, alkaline earth metal components, heat resistant metal oxide support materials, etc.) present in the coating and the size of the oxidation catalyst (e.g. , the size of the support, which will vary depending on the application of the catalyst).

Typically, drying conditions include drying the coating for at least 15 minutes, preferably at least 20 minutes. Under such conditions, uneven distribution of the first platinum group metal and the optional alkaline earth metal can be obtained. Uniform distributions are generally obtained when the drying time is approximately 5 minutes or less.

Then the coating can be calcined at a temperature of from 400 to 800°C, preferably from 450 to 600°C, more preferably at a temperature of at least 500°C.

For example, it has been found that if the first porous oxide catalytic coating layer has a first load and a weight ratio of platinum and palladium as two or more platinum group metal components and one or more alkaline earth metal components is barium, wherein both the platinum group metals and barium are deposited on a refractory metal oxide support material, which is silica-doped alumina, with a preferred content of silica, and such a first porous oxide catalytic coating layer is impregnated with an aqueous solution of relatively highly concentrated salts of platinum and palladium to form the first zone of the porous oxide catalytic coating after applying the drying methods described above, palladium and barium more easily migrate to the exposed surface of the porous oxide catalytic coating layer and observe Xia in the form of a "crust" when analyzed by the EPMA method. Without prior fixation on the underlying refractory metal oxide substrate material, the platinum component exhibits some mobilization towards the same exposed surface within the cross section of the first porous oxide catalytic coating layer, remaining relatively more evenly distributed over the cross section of the first porous catalytic coating layer. oxide than palladium and barium. It was found that the finished product shows a favorable activity in terms of generating an exothermic effect. This effect is also shown in part in Example 2 below in this document.

Exhaust systems

Exhaust systems according to a second aspect of the invention comprise a composite oxidation catalyst according to the invention and a downstream particulate filter substrate, with a first end of the composite oxidation catalyst substrate oriented upstream.

The particulate filter substrate can be coated with a catalyst composition and is usually coated with it.

The diesel particulate filter catalyst composition may be suitable for oxidizing: (i) particulate matter (PM) and/or (ii) carbon monoxide (CO) and hydrocarbons (HC). If the catalyst composition is suitable for PM oxidation, the resulting emission control device is referred to as a catalyzed diesel particulate filter (CSF). Typically, the composition of the catalyst in CSF includes a platinum group metal, such as a first platinum group metal and/or a second platinum group metal, as defined above.

SCR catalysts are also well known in the art and can be supported on a flow support or on a filter support such as a flow wall filter support. When the exhaust system of the invention comprises an SCR catalyst, for example deposited on a flow-through substrate monolith, the exhaust system may further comprise an injector for injecting a nitrogenous reducing agent, such as ammonia or urea, into the exhaust gas downstream of the monoxide oxidation catalyst. carbon (CO) and hydrocarbons (HC), in this case a composite oxidation catalyst according to the invention or a CSF catalyst located downstream of the composite oxidation catalyst according to the invention and upstream of the SCR catalyst. The exhaust system may further comprise an engine control means for enriching the exhaust gas with hydrocarbons to bring the oxidation catalyst composite into contact with hydrocarbons and generate an exothermic effect to regenerate the downstream particulate filter. In an alternative or additional embodiment, the introduction of hydrocarbons may be facilitated by a self-contained hydrocarbon injector for injecting hydrocarbon fuel into the exhaust gas downstream of the engine manifold but upstream of the composite oxidation catalyst.

In an alternative embodiment of the CSF catalyst formulation, the particulate filter substrate, preferably a flow wall filter, may be coated with an SCR catalyst, in which case it is referred to as a SCRF catalyst.

Typically, SCR catalysts cannot reduce significant amounts of NO _x in the exhaust gas shortly after starting a compression ignition engine because the temperature of the exhaust gas (and hence the temperature of the catalyst) is too low. NO _x trap catalysts for lean conditions (e.g. NO _x adsorption catalysts) are used, for example, upstream of the SCR catalysts so that the NO _x can be stored until the SCR catalyst becomes active at higher exhaust gas temperatures. However, lean NO _x trap catalysts are often unable to adequately store NO _x in the presence of a high exhaust gas mass flow rate (eg, when an engine is running in a high speed cycle).

In accordance with the second aspect of the invention, the exhaust systems used in the present invention are shown in the accompanying FIGS. 8A–D. The first embodiment of the exhaust system (see FIG. 8A) includes a composite oxidation catalyst of the invention on a honeycomb flow-through support monolith (see item 42 in FIG. 8A) and a selective catalytic reduction filter (SCRF). Such a configuration may be referred to as DOC/SCRF. This embodiment also relates to the use of a composite oxidation catalyst for treating exhaust gas from an internal combustion engine, in particular a compression ignition engine, in combination with a selective catalytic reduction (SCRF) filter catalyst. Preferably, the composite oxidation catalyst is or is intended to be used as such a diesel oxidation catalyst. The composite oxidation catalyst of the invention is usually followed by, i. located downstream, the selective catalytic reduction (SCRF) filter catalyst. The nitrogenous reductant injector may be located between the composite oxidation catalyst and the selective catalytic reduction (SCRF) filter catalyst. Thus, the composite oxidation catalyst may be followed (i.e., it may be located downstream of it) by a nitrogen reductant injector, and the nitrogen reductant injector may be followed by (i.e., it may be located downstream of it ) selective catalytic reduction (SCRF) catalyst-filter.

In a second embodiment of the exhaust system (see Fig. 8B), the exhaust system comprises a composite oxidation catalyst of the invention on a honeycomb flow-through substrate monolith and either a (non-catalyzed) diesel engine dust filter (DPF) or a catalyzed diesel particulate filter (CSF). ). Such a configuration may be referred to as DOC/DPF or DOC/CSF. This embodiment also relates to the use of a composite oxidation catalyst for purifying exhaust gas from an internal combustion engine, in particular a compression ignition engine, in combination with a diesel engine particulate filter or a catalyzed particulate filter. Preferably, the composite oxidation catalyst is or is intended to be used as a diesel oxidation catalyst. The composite oxidation catalyst is typically followed by (ie downstream of) a diesel engine dust filter or catalyzed particulate filter (CSF). Thus, for example, the outlet of the composite oxidation catalyst is connected to the inlet of a diesel engine dust filter or a catalyzed particulate filter.

A third embodiment of an exhaust system (see Fig. 8C) relates to an exhaust system comprising a composite oxidation catalyst of the invention on a honeycomb flow-through substrate monolith, a diesel engine dust filter or a catalyzed particulate filter (CSF), and a selective catalytic reduction catalyst. (SCR). Such a configuration may be referred to as DOC/DPF/SCR or DOC/CSF/SCR. This embodiment also relates to the use of a composite oxidation catalyst for purifying exhaust gas from an internal combustion engine, in particular a compression ignition engine, in combination with a diesel engine particulate filter or catalyzed particulate filter (CSF) and a selective catalytic reduction (SCR) catalyst, wherein the oxidation catalyst is preferably or intended to be a diesel oxidation catalyst. The composite oxidation catalyst is typically followed by (ie downstream of) a diesel engine particulate filter or catalyzed particulate filter (CSF). The DPF or CSF is typically followed by (ie downstream of) a selective catalytic reduction (SCR) catalyst. The nitrogen reductant injector may be located between the DPF or CSF and the selective catalytic reduction (SCR) catalyst. Thus, the DPF or CSF catalyst may be followed by (i.e. downstream of) a nitrogen reductant injector, and the nitrogen reductant injector may be followed by (i.e. downstream of) an injector selective catalytic reduction (SCR) catalyst.

The fourth embodiment of the exhaust system (see Fig. 8A) relates to an exhaust system comprising a composite oxidation catalyst of the invention on a flow wall substrate monolith (CSF - see item 42 in Fig. 8A) and a selective catalytic reduction catalyst (SCR). This also applies to the CSF/SCR configuration. A further aspect of this embodiment relates to the use of a composite oxidation catalyst for purifying exhaust gas from a compression ignition engine in combination with a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) catalyst, the composite oxidation catalyst being preferably a catalyzed particulate filter ( CSF) or intended to be used as such. The diesel oxidation catalyst (DOC) is typically followed by (ie, located downstream of) a composite oxidation catalyst of the invention. The composite oxidation catalyst of the invention is typically followed by (ie downstream of) a selective catalytic reduction (SCR) catalyst. The nitrogen reductant injector may be located between the oxidation catalyst and the selective catalytic reduction (SCR) catalyst. Thus, the composite oxidation catalyst may be followed by (eg, downstream of) a nitrogen reductant injector, and the nitrogen reductant injector may be followed by (eg, downstream of) a selective catalytic reduction (SCR) catalyst.

In a fifth embodiment of the exhaust system (see Fig. 8D), the exhaust system comprises a composite oxidation catalyst of the invention, preferably in the form of a DOC, a selective catalytic reduction (SCR) catalyst, and either a catalyzed diesel particulate filter (CSF) or a particulate filter. diesel engine (DPF). The configuration is either DOC/SCR/CSF or DOC/SCR/DPF. This embodiment also relates to the use of a composite oxidation catalyst for purifying exhaust gas from an internal combustion engine, in particular a compression ignition engine, in combination with a selective catalytic reduction (SCR) catalyst and either a catalyzed diesel particulate filter (CSF) or a diesel particulate filter. engine (DPF), and the composite oxidation catalyst is preferably a diesel oxidation catalyst, or is intended for use as such.

Such structures are shown in Fig. 8A-D, respectively, wherein element 30 is a heavy duty diesel engine; element 32 is an exhaust system for a heavy duty diesel engine; member 34 is a pipe for supplying exhaust gas from a heavy duty diesel engine to or from the exhaust system component (42, 44, 50) to atmosphere 36; element 38 is an injector for injecting hydrocarbon fuel into the exhaust gas downstream of the engine manifold 40 and upstream of the composite oxidation catalyst 42 in accordance with the present invention, such as any of those composite oxidation catalysts shown in FIG. 1-5 inclusive, wherein the first zone 1 of the porous oxide catalytic coating is oriented upstream, the substrate of the composite oxidation catalyst may be a flow-through support monolith or a flow wall filter support monolith; item 44 is a diesel engine dust filter (DPF) or a catalyzed particulate filter (CSF); element 46 is an injector for injecting liquid nitrous reductant precursor, such as urea, held in reservoir 48 into the exhaust gas stream; element 50 is a selective catalytic reduction (SCR) catalyst supported on a flow-through support monolith or flow wall filter support (SCRF) monolith.

In addition to the appended claims, the invention may be defined in accordance with one or more of the following definitions:

1. A composite oxidation catalyst for use in an exhaust system for purifying exhaust gas produced by an internal combustion engine for a compression ignition vehicle, preferably for a heavy duty diesel vehicle, and located upstream in the exhaust system downstream of the particulate filter, wherein the composite oxidation catalyst comprises:

a substrate having an overall length L and a longitudinal axis and having a substrate surface extending in the axial direction between the first end of the substrate and the second end of the substrate; and

two or more porous oxide catalytic coating zones arranged sequentially in the axial direction on and along the surface of the substrate, wherein the first porous oxide catalytic coating zone having a length L ₁ , where L ₁ <L, is formed at one end by the first end of the substrate , and at the second end - the first end of the second zone of the catalytic coating of the porous oxide, having a length L ₂ , and L ₂ <L, wherein the first zone of the catalytic coating of the porous oxide contains the first substrate material of heat-resistant metal oxide and two or more deposited on it components representing a metal of the platinum group, containing both platinum and palladium with a mass ratio of platinum and palladium ≥1; and the second zone of the porous oxide catalytic coating comprises a second material-substrate of a heat-resistant metal oxide and one or more platinum group metal components deposited thereon,

wherein the total platinum group metal loading in the first zone of the porous oxide catalytic coating, expressed as grams of platinum group metals per cubic foot of substrate volume (g/ft ³ ), is greater than the total platinum group metal load in the second zone of the porous oxide catalytic coating, and wherein the first porous oxide catalytic coating zone comprises one or more first alkaline earth metal components deposited on a first refractory metal oxide substrate material.

2. The composite oxidation catalyst of claim 1, wherein the second zone of the porous oxide catalytic coating is formed at its second end by the second end of the support.

3. The composite oxidation catalyst of claim 1, comprising three or more porous oxide catalytic coating zones, the third porous oxide catalytic coating zone comprising a third refractory metal oxide support material and one or more components deposited thereon, which are platinum group metal is formed at its second end by the second end of the support, and wherein the total load of platinum group metals in the third zone of the porous oxide catalytic coating, expressed in grams of platinum group metal per cubic foot of support volume (g/ft ³ ), is less than the total loads of platinum group metals in the second zone of the porous oxide catalytic coating.

4. The composite oxidation catalyst of claim 3, comprising four porous oxide catalytic coating zones, wherein the fourth porous oxide catalytic coating zone is located between the second porous oxide catalytic coating zone and the third porous oxide catalytic coating zone, the fourth zone of catalytic porous oxide coating from porous oxide contains a fourth material-substrate of heat-resistant metal oxide and one or more components deposited on it, representing a platinum group metal, and is formed at the first end by the second end of the second zone of the porous oxide catalytic coating, and at the second end by the first end of the third porous oxide catalytic coating zones, and wherein the total platinum group metal loading in the fourth porous oxide catalytic coating zone, expressed in grams of platinum group metal per cubic foot of substrate volume (g/ft ³ ), is greater than the total platinum group metal loading pps in each of the second porous oxide catalytic coating zone and the third porous oxide catalytic coating zone.

5. The composite oxidation catalyst of claim 4, comprising a first porous oxide catalytic coating layer and a second porous oxide catalytic coating layer, wherein the first porous oxide catalytic coating layer comprises a refractory metal oxide substrate material and one or more the platinum group metal component has a length L ₃ , with L ₃ <L, and is formed at one end by the first end of the substrate; and the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₄ , where L ₄ <L, and is formed at the second end by the second end of the substrate , wherein the fourth porous oxide catalytic coating zone comprises a two-layer area of overlap of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer, and wherein the third porous oxide catalytic coating zone comprises one layer of the second porous oxide catalytic coating layer A that is not formed from the overlap region.

6. The composite oxidation catalyst of claim 3, comprising three porous oxide catalytic coating zones, wherein the third porous oxide catalytic coating zone is formed at its first end by the second end of the second porous oxide catalytic coating zone.

7. The composite oxidation catalyst of claim 6, comprising a first porous oxide catalytic coating layer and a second porous oxide catalytic coating layer, wherein the first porous oxide catalytic coating layer comprises a refractory metal oxide substrate material and one or more the platinum group metal component has a length L ₃ , with L ₃ <L, and is formed at one end by the first end of the substrate; and the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₄ , where L ₄ <L, and is formed at the second end by the second end of the substrate , wherein the second porous oxide catalytic coating zone comprises a two-layer area of overlap of the first porous oxide catalytic coating layer and the second porous oxide catalytic coating layer, and wherein the third porous oxide catalytic coating zone comprises one layer of the second porous oxide catalytic coating layer A that is not formed from the overlap region.

8. Composite oxidation catalyst according to any one of paragraphs. 1–7, in which the mass ratio of platinum and palladium in the first zone of the porous oxide catalytic coating is 10 : 1 ≥ 1.5 : 1.

9. Composite oxidation catalyst according to any one of paragraphs. 2-7, wherein the porous oxide catalytic coating zone formed at its second end by the second end of the substrate contains manganese and/or the second porous oxide catalytic coating layer contains manganese.

10. The composite oxidation catalyst of claim 9, wherein the refractory metal oxide support material in the manganese-containing zone or layer comprises silica-doped alumina, manganese-doped alumina, both silica-doped alumina and and manganese, magnesium-aluminum mixed oxide, or magnesium-aluminum mixed oxide doped with manganese.

11. The composite oxidation catalyst of claim 9 or 10, wherein the impregnating manganese component is applied to a refractory metal oxide support material.

12. Composite oxidation catalyst according to any one of paragraphs. 3-11, wherein one or more of the platinum group metal components in the second porous oxide coating layer or in the third zone of the porous oxide catalytic coating consist essentially of platinum.

13. Composite oxidation catalyst according to any one of paragraphs. 5-12, wherein two or more platinum group metal components in the first porous oxide catalytic coating layer consist of both platinum and palladium.

14. Composite oxidation catalyst according to any one of paragraphs. 1-13 in which the total platinum group metal loading in the first zone of the porous oxide catalytic coating is <100 g/ft ³ on an elemental metal basis.

15. Composite oxidation catalyst according to any one of paragraphs. 1-14, wherein one or more platinum group metal components in the second zone of the porous oxide catalytic coating contain both platinum and palladium.

16. The composite oxidation catalyst of claim 15, wherein the weight ratio of platinum to palladium in the second zone of the porous oxide catalytic coating is greater than the weight ratio of platinum to palladium in the first zone of the porous oxide catalytic coating.

17. Composite oxidation catalyst according to any one of paragraphs. 4–16, in which the mass ratio of platinum and palladium in each subsequent porous oxide catalytic coating zone located sequentially along the length L of the substrate after the first porous oxide catalytic coating zone is greater than in the immediately preceding porous oxide catalytic coating zone.

18. Composite oxidation catalyst according to any one of paragraphs. 1-17, in which L ₁ is <50% L.

19. Composite oxidation catalyst according to any one of paragraphs. 1-18, having a total load of platinum group metals on the substrate generally in the range of 5-60 g/ft ³ based on the elemental metal.

20. Composite oxidation catalyst according to any one of paragraphs. 1–19, in which the total mass ratio of Pt : Pd in the composite oxidation catalyst as a whole is from 3 : 2 to 9 : 1.

21. Composite oxidation catalyst according to any one of paragraphs. 1-20, in which the total load of alkaline earth metals in the first zone of the porous oxide catalytic coating is 10-100 g/ft ³ in terms of elemental metal.

22. Composite oxidation catalyst according to any one of paragraphs. 1–21, in which the mass ratio of the total amount of elemental alkaline earth metal and the total amount of elemental platinum group metal in the first zone of the porous oxide catalytic coating is < 1 : 1.

23. Composite oxidation catalyst according to any one of paragraphs. 1-22, wherein the alkaline earth metal in the first zone of the porous oxide catalytic coating contains barium (Ba) or strontium (Sr), preferably Ba.

24. Composite oxidation catalyst according to any one of paragraphs. 1-23, in which the first zone of the porous oxide catalytic coating has an uneven distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate, according to electron probe microanalysis (EPMA), wherein the concentration of one or more platinum group metal components and/or the first alkaline earth metal component decreases in a direction perpendicular to the surface of the substrate.

25. Composite oxidation catalyst according to any one of paragraphs. 1-24, wherein at least the first refractory metal oxide substrate material comprises alumina doped with a heteroatom, preferably silica.

26. Composite oxidation catalyst according to any one of paragraphs. 1-25, comprising an outer porous oxide coating layer extending axially from the first end of the substrate to protect at least a portion of the underlying first porous oxide coating zone from phosphorus and/or zinc poisoning during operation, wherein the outer coating layer of porous the oxide has a load of metal oxide powder >0.8 g/in ³ .

27. The composite oxidation catalyst of claim 26, wherein the particulate metal oxide in the outer porous oxide coating layer has an average pore diameter of ≥10 nm and/or the outer porous oxide coating layer has an average interparticle pore diameter of ≥10 nm.

28. The composite oxidation catalyst of claim 26 or 27, wherein the particulate metal oxide in the outer layer of the porous oxide coating is selected from the group consisting of alumina, silica, titanium oxide, zirconium oxide, cerium oxide, and a mixed or composite oxide of any two or more of them or an aluminosilicate zeolite.

29. The composite oxidation catalyst of claim 26, 27, or 28, wherein the metal oxide powder in the outer layer of the porous oxide coating has a specific surface area >100 m ² /g.

30. Composite oxidation catalyst according to any one of paragraphs. 26–29, in which a platinum group metal, which is platinum or a combination of platinum and palladium at a mass ratio of Pt : Pd ≥ 1 : 1, is deposited on the powder metal oxide in the outer layer of the porous oxide coating.

31. The composite oxidation catalyst of claim 30, wherein the platinum group metal loading in the outer layer of the porous oxide coating is 1-35 g/ft ^-3 .

32. Composite oxidation catalyst according to any one of paragraphs. 1–31, in which the substrate is a flow-through substrate monolith with a honeycomb structure.

33. An exhaust system for a vehicle engine with compression ignition, containing a composite oxidation catalyst in accordance with any one of paragraphs. 1-32 and a particulate filter substrate located downstream of the composite oxidation catalyst, with the first end of the oxidation catalyst substrate oriented upstream.

34. The exhaust system of claim 33, wherein the particulate filter substrate is a catalyzed particulate filter substrate that is catalyzed by a platinum group metal catalyst or a selective catalytic reduction catalyst.

35. The exhaust system according to claim 33 or 34, comprising a liquid hydrocarbon injector connected to a source of liquid hydrocarbon, the injector being configured to inject liquid hydrocarbon into the exhaust gas flowing in the exhaust system downstream of the engine.

36. An exhaust system according to claim 33, 34, or 35, comprising a substrate located downstream of the particulate filter substrate and catalyzed by a selective catalytic reduction catalyst.

37. An exhaust system according to claim 34, 35, or 36, comprising a selective catalytic reduction catalyst, wherein the system comprises an injector for a nitrogenous reductant or a precursor thereof connected to a source of a nitrogenous reductant or a nitrogenous reductant precursor, the injector being configured to introduce a nitrogenous reductant or a nitrogenous reductant precursor to the exhaust gas stream downstream of the composite oxidation catalyst and upstream of the substrate containing the selective catalytic reduction catalyst.

38. Internal combustion engine with compression ignition for a vehicle with a diesel engine for heavy duty, containing the exhaust system according to any one of paragraphs. 33-37, wherein the first end of the composite oxidation catalyst support is oriented upstream.

39. A heavy duty diesel engine vehicle containing a compression ignition internal combustion engine in accordance with paragraph 38.

40. The use of a composite oxidation catalyst according to any one of paragraphs. 1-32 for heating a diesel particulate filter downstream of a composite oxidation catalyst in the exhaust system of an internal combustion engine for a compression ignition vehicle by generating an exothermic effect by increasing the concentration of hydrocarbon fuel in the exhaust gas flowing through the exhaust system. exhaust gases compared to normal operating conditions by bringing the oxidation catalyst into contact with an exhaust gas containing an increased concentration of hydrocarbon fuel.

41. A method for producing a composite oxidation catalyst for use in an exhaust system for purifying exhaust gas produced by an internal combustion engine for a compression ignition vehicle, the composite oxidation catalyst comprising:

a substrate having an overall length L and a longitudinal axis and having a substrate surface extending in the axial direction between the first end of the substrate and the second end of the substrate; and

two or more porous oxide catalytic coating zones arranged sequentially in the axial direction on and along the surface of the substrate, wherein the first porous oxide catalytic coating zone having a length L ₁ , where L ₁ <L, is formed at one end by the first end of the substrate , and at the second end - the first end of the second zone of the catalytic coating of the porous oxide, having a length L ₂ , and L ₂ <L, wherein the first zone of the catalytic coating of the porous oxide contains the first substrate material of heat-resistant metal oxide and two or more deposited on it components representing a platinum group metal containing both platinum and palladium with a mass ratio of platinum and palladium ≥1; and the second zone of the porous oxide catalytic coating contains a second material-substrate of a heat-resistant metal oxide and one or more components deposited on it, which is a platinum group metal,

wherein the total platinum group metal load in the first zone of the porous oxide catalytic coating, expressed as grams of platinum group metals per cubic foot of support volume (g/ft ³ ), is greater than the total platinum group metal load in the second zone of the porous oxide catalytic coating, and wherein the first porous oxide catalytic coating zone comprises one or more first alkaline earth metal components deposited on a first heat resistant metal oxide substrate material, the method comprising the steps of:

(a) depositing a catalytic porous oxide coating layer on the surface of a substrate from one end of the substrate, the catalytic porous oxide coating layer comprising a heat resistant metal oxide substrate material and one or more platinum group metal components; and

(b) impregnating the porous oxide catalytic coating layer in a zone of length L ₁ formed at one end by the first end of the substrate with a solution containing one or more platinum group metals,

wherein one or more alkaline earth metal components are present in the porous oxide catalytic coating layer in step (a) and/or in the impregnation solution used in step (b).

42. The method of claim 41, wherein in step (a) the porous oxide catalytic coating extends along the entire length L of the substrate.

43. The method of claim 41, wherein in step (a) the porous oxide catalytic coating layer is a first porous oxide catalytic coating layer that extends from the first end of the substrate to a length less than the overall length of the substrate, the method further comprising step (a') before step (a) or after step (a), but in any case before step (b) of applying a second layer of porous oxide catalytic coating on the substrate from the second end of the substrate to a length less than the total length of the substrate so that the first the porous oxide catalytic coating layer partially overlapped the second porous oxide catalytic coating layer or the second porous oxide catalytic coating layer partially overlapped the first porous oxide catalytic coating layer, the second porous oxide catalytic coating layer comprising a heat-resistant metal oxide substrate material and one or more platinum metal components th group.

44. The method of claim 43, wherein the first porous oxide catalytic coating layer extends from the first end of the substrate and the second porous oxide catalytic coating layer extends from the second end of the substrate, wherein the second porous oxide catalytic coating layer partially overlaps the first catalytic layer. porous oxide coatings.

Definitions

Any reference to a distribution of platinum group metals (e.g., a first platinum group metal or a second platinum group metal) in a direction (e.g., in a straight line) perpendicular to the substrate surface essentially refers to a direction perpendicular to the same surface of the substrate on which the catalyst layer is located. . By way of reference, the surface of the substrate is in a substantially horizontal (ie, longitudinal) plane. The direction perpendicular to the surface of the substrate is generally the direction in the cross-sectional plane through the catalyst layer (ie, in the cross-sectional plane that exposes the thickness of the catalyst layer) perpendicular to the surface of the substrate. The cross-sectional plane is essentially in a vertical (ie transverse) plane. The cross-sectional plane is perpendicular to the surface on which the catalyst layer is located. More typically, the cross-sectional plane is substantially parallel to the surface of the inlet end of the substrate and/or the surface of the outlet end of the substrate (ie, the plane containing the inlet end of the substrate and/or the plane containing the outlet end of the substrate). Any reference to the term "substantially parallel" in this context refers to an angle of less than 5°, preferably less than 2.5°, more preferably less than 1° (eg, less than 0.5°) between the cross-sectional plane and the inlet or outlet end of the substrate.

Any reference to the term "substrate surface" essentially refers to the wall surface of the channel passing through the substrate.

As used herein, the term “layer” (e.g., catalyst layer) refers to the thickness of material distributed over a surface, such as the surface of a substrate or the surface of another layer, which typically has distinct boundaries or edges (i.e., can be distinguished the first layer from a second layer of a different composition using traditional analytical techniques (for example, transmission electron microscopy).

The term "homogeneous" as used herein in relation to the distribution of platinum group metal essentially refers to a composition (e.g. layer) in which the amount of platinum group metal at any point in the composition is within ±20% of the average amount of platinum group metal during the entire composition (for example, a layer). Preferably, the amount of platinum group metal at any point in the composition is within ±10%, more preferably ±5%, and even more preferably ±1% of the average amount of platinum group metal in the entire composition (eg, layer). The average amount of platinum group metal should correspond to the amount of platinum group metal measured upon receipt of this composition. The amount of platinum group metal at any point in the composition can be determined using standard analytical techniques such as EDX analysis using a transmission electron microscope.

As used herein, the term "mixed oxide" essentially refers to a mixture of oxides in one phase, as is conventionally known in the art.

As used herein, the term "composite oxide" essentially refers to a composition of oxides with more than one phase, as is conventionally known in the art.

The term "load" is used to refer to the concentration of a component, such as a platinum group metal component, an alkaline earth metal component, or a porous oxide coating composition containing both one or more platinum group metal components and one or more than the alkaline earth metal components deposited on the heat-resistant metal oxide substrate material present in the porous oxide catalytic coating zone, in the porous oxide catalytic coating layer, or present as a whole on the substrate. EPMA or XRF techniques can determine the local concentrations of the platinum group metal components, or each of them, or the alkaline earth metal component, or each such component. Load units used here and in the prior art are generally expressed in g·ft ^-3 or g·in ^-3 or equivalent SI units (grams per litre) and refer to the volume of substrate used. The component volume is considered to be the volume of the substrate on which, for example, a porous oxide coating layer is applied. Generally, components of relatively low concentration are given in g ft ^-3 to provide a more convenient indication of the quantity without the need for 100th or 1000th parts, while components with a higher concentration are indicated g inch ^-3 , for example, at an indication of the total amount of porous oxide coating to be applied. It has been agreed that the "volume" component of load units implies that the substrate is a solid, e.g., the total volume of a cylinder, and to ignore that the substrate has channels through it formed by walls made from the substrate composition, or that the substrate composition is inherently is porous.

The term "comprising" means that the named elements are mandatory, but other elements may be added that still form a construct that is within the scope of the claims.

The expression "substantially" used herein can be replaced by the broader term "comprising" and limits the scope of the feature to include the materials or steps specified and any other materials or steps that do not significantly affect the underlying and novel the characteristics and functions of that feature, or that feature in combination with other features of the invention. If the porous oxide catalytic coating zone consists essentially of platinum, this means that it must be composed of platinum, but other platinum group metal(s) may unintentionally be present in the porous oxide catalytic coating zone of the finished product, for example palladium, due to the migration of palladium into the porous oxide catalytic coating zone during production. In this context, the term "consisting essentially of" does not preclude the unintentional presence of palladium in the zone of the porous oxide catalytic coating, defined as being essentially composed of platinum. The term "consisting essentially of" includes the expression "consisting of" and is interchangeable with the term "comprising" or "consisting of". The term "consisting of" means the absence of the possibility of inclusion in the patent claims of materials other than those listed, with the exception of impurities usually associated with them.

With regard to the composite oxidation catalyst in accordance with the invention, the basic and new features of the invention are a substrate of at least two porous oxide catalytic coating zones located in series in the axial direction on the surface of the substrate and along it, and the first porous oxide catalytic coating zone , formed at one end by the inlet end of the substrate, includes a heat-resistant metal oxide substrate material, both platinum and palladium in a mass ratio of Pt : Pd ≥1 and barium, and the second porous oxide catalytic coating zone includes a substrate material of a heat-resistant metal oxide and either platinum as the only platinum group metal present, or platinum and palladium in a Pt:Pd weight ratio greater than in the first porous oxide coating zone.

In the context of the expression "platinum group metal" (for example, the first platinum group metal or the second platinum group metal), it should be understood that it is often difficult to characterize the exact catalytic forms in the catalyst, and the platinum group metal may be present in a non-elemental metallic form. Any reference to the term "consisting essentially of a platinum group metal..." includes a "platinum group metal functional group" in the elemental form of a platinum group metal, an alloy containing a platinum group metal, or a compound containing a platinum group metal (e.g., oxide platinum group metal). Preferably any such "platinum group metal functional group" is an elemental form of a platinum group metal or an alloy containing a platinum group metal, more preferably an elemental form of a platinum group metal.

According to the embodiment of claim 2 and FIG. 1, in which the first and second catalytic porous oxide coating layers are adjacent to each other "substantially without overlap between the first and second porous oxide coating layers", the term "substantially without overlap" should cover coating products in which between the first there is no gap between the porous oxide catalytic coating and the second porous oxide catalytic coating. In practice, it is very difficult in practice to obtain an ideal "gapless" coating, in which there is no overlap between two layers of porous oxide composite coating at the junction between them. Thus, in practice, products made by the methods embodied in the sixth aspect of the invention may have unintentional overlap from a value of 1-2 mm to 15% of the axial length, for example up to 14%, 13%, 12%, 11%, 10% , 9%, 8%, 7%, 8%, 6%, 5%, 4%, 3%, 2% or 1%. Accordingly, the composite oxidation catalyst according to the first aspect extends to products having an inadvertent overlap to the specified size.

EXAMPLES

The invention will be illustrated below with the help of the following non-limiting examples. For the avoidance of doubt, all coating steps were carried out using the methods and apparatus described in the Applicant's publication WO 99/47260, i.e., were the steps in which: (a) placing the retention means on top of the substrate, (b ) dispensed a predetermined amount of liquid component into said holding means, or in the following order: (a) then (b) or (b) then (a), and (c) vacuum was applied to completely draw said amount of liquid component into at least part of the substrate, and retaining essentially all of the specified amount inside the substrate without recirculation.

Example 1 (comparative)

A bare cordierite flow-through honeycomb substrate monolith with a density of 400 cells per square inch, a wall thickness of 6 thousand inches (6 mils), and a total length of 4 inches was coated with a porous oxide catalytic coating in a zonal configuration as follows. The first suspension of a porous oxide catalytic coating containing aqueous salts (in the form of nitrates) of platinum and palladium and an alumina support doped with 5 wt.% silicon dioxide was applied to the substrate monolith to an axial length of 75% of the total length of the substrate monolith from one end labeled as the inlet end. The platinum and palladium salt concentrations were chosen to provide a coating load of 6.67Pt : 3.33Pd g ft ^-3 at a platinum to palladium weight ratio of 2 : 1 in the first porous oxide catalytic coating. This inlet coating was then dried in a conventional oven in for 1 hour at 100°C to remove excess water and other volatiles.

A second porous oxide catalytic coating slurry containing a saline solution of platinum nitrate as the only platinum group metal present and 5 wt % of a silica doped alumina support was applied to the substrate from the end of the substrate monolith opposite the end from which the first was applied coverage, i.e. from graduation. The axial length of the second porous oxide catalytic coating was 50% of the total length of the substrate, i.e. 25% of the second porous oxide catalytic coating overlapped with the first porous oxide catalytic coating. The platinum salt concentration applied was chosen to give a load of 2 g ft ^-3 Pt per 50% of the axial length of the substrate. The substrate coated with both the first and second porous oxide coatings was dried in a conventional oven for 1 hour at 100°C, and then the dried portion was calcined for 1 hour at 500°C to decompose platinum and palladium salts and fix platinum and palladium on a silica-doped alumina substrate.

Then, the first porous oxide catalytic coating over 25% of the axial length of the substrate, starting from the inlet end of the substrate, was impregnated with an aqueous medium containing salts of platinum nitrate and palladium nitrate in a weight ratio of 1:1. ^-3 for both platinum and palladium on the impregnated length of the substrate. This provides a high PGM load in the inlet end zone with an additional load of 50 g ft ^-3 over the load of the underlying first porous oxide catalytic coating. The impregnated portion was dried in an oven and calcined as described above.

All porous oxide coatings and impregnation solutions were inherently acidic and no pH adjustments were made.

The final product contained a substrate monolith having three zones of porous oxide catalytic coating arranged in series in the axial direction: the first, a highly loaded front zone formed by approximately 25% of the axial length of the substrate monolith as measured from the inlet end and having a total load of platinum group metals , which is a combination of the underlying first catalytic coating of porous oxide with a ratio of 2 Pt : 1 Pd and impregnation with a ratio of 1 : 1 Pt : Pd; an axially following second porous oxide catalytic coating zone, consisting of a first porous oxide catalytic coating with a ratio of 2 Pt : 1 Pd, over approximately 50% of the axial length of the substrate monolith, having a lower total load of platinum group metals than the first catalytic zone porous oxide coatings; and finally a third Pt-only zone at the outlet end formed from the second porous oxide catalytic coating over approximately 25% of the axial length of the substrate monolith having a lower total platinum group metal load than the first or second porous oxide catalytic coating zones. . The total load of platinum group metals on the substrate monolith as a whole was 20 g ft ^-3 with a total Pt : Pd mass ratio of 11.8 : 4, which is equivalent to 2.95 : 1.

By means of image analysis of EPMA-WDX (electron microprobe analysis - wavelength dispersive X-ray analysis), it was found that the thus obtained first porous oxide catalytic coating zone, which contained a high concentration of platinum and palladium, had an uneven distribution of Pd in the direction perpendicular to substrate surface, i.e. the amount of Pd decreased in the direction perpendicular to the substrate surface. In other words, the concentration of Pd at the top surface of the porous oxide coating layer in contact with the gas entering the inlet end of the substrate was higher than that of the porous oxide coating layer near the surface of the substrate. In addition, it was found that platinum, although to a lesser extent, was subject to the same rule as palladium. However, the uneven distribution of Pd in the direction perpendicular to the substrate surface in the first zone of the porous oxide catalytic coating was most pronounced. This effect is referred to herein as the formation of a so-called "skin" of Pd in the first zone of the porous oxide catalytic coating.

Example 2

A product identical to that described in Comparative Example 1 was prepared, except that, in addition to the aqueous platinum and palladium salts, the first porous oxide catalytic coating slurry contained an aqueous barium acetate salt according to the invention. The barium acetate concentration was chosen such that the barium load in the first porous oxide catalytic coating was 80 g ft ^-3 for 75% of the axial length of the first porous oxide catalytic coating. Thus, the first and second zones of the porous oxide catalytic coating contained barium with a load of 80 g ft ^-3 . The total platinum group metal load and Pt : Pd weight ratio on the substrate monolith were generally the same as in Example 1, i.e. 20 g ft ^-3 .

It was found that using EPMA-WDX image analysis, the first zone of the porous oxide catalytic coating thus obtained has the amount of Pd decreasing in the perpendicular direction towards the surface of the substrate, and to a lesser extent, the same distribution of Pt, but also relatively strong. uneven distribution of barium, which decreases in a perpendicular direction towards the surface of the substrate. In other words, both Pd and Ba (and to a lesser extent Pt) form a "skin" on the surface of the porous oxide coating layer in contact with the gas entering the inlet end of the substrate.

Example 3 Test Method and Results for Comparing Options with and without Barium in the Inlet Zone

Thermal analysis of each composite oxidation catalyst obtained in accordance with examples 1 and 2, inclusive, was carried out using a diesel engine installed on a laboratory bench. The engine was supplied with EUVI B7 fuel (7% biofuel) both for engine operation and for enriching the exhaust gas with hydrocarbons (exotherm generation), the engine was operated at 2200 rpm and was equipped with an exhaust gas system containing an exhaust pipe and a removable a beaker into which each of the composite oxidation catalysts could be inserted for testing so that the inlet end/first catalyst with the high load porous oxide coating zone was oriented upstream. The engine was a 7 liter 6-cylinder EUV engine developing 235 kW at 2500 rpm, and the exhaust system included a "7th ^injector " positioned to inject hydrocarbon fuel directly into the downstream exhaust gas line. downstream of the engine manifold and upstream of the tested composite oxidation catalyst. This injector is called the " ^7th injector" because it is in addition to the six fuel injectors associated with the engine's cylinders. Thermocouples were placed at the inlet of the composite oxidation catalyst and at various axial positions along the center line of the substrate monolith of each composite oxidation catalyst.

Each catalyst was conditioned for 10 minutes at an exhaust gas inlet temperature of 490° C. and an exhaust gas flow rate of 1000 kg/hr, followed by a rapid cooling step. The exhaust gas flow rate was then set to 720 kg/h (corresponding to 120,000 h ^-1 space velocity at the substrate size and volume tested), with the engine load adjusted to provide a stable set exhaust gas inlet temperature of about 270°C. for approximately 1800 seconds.

The ability of the composite oxidation catalyst to generate an exothermic effect at each given stabilized temperature was then tested by injecting hydrocarbon fuel through the 7th ^injector , focusing on a temperature of 600°C and a stable hydrocarbon "breakthrough" at the exit of the composite oxidation catalyst substrate, measured by a downstream thermocouple. and hydrocarbon sensors. The test was terminated if hydrocarbon slip, measured downstream of the composite oxidation catalyst, exceeded 1000 ppm. C ₃ , i.e. regardless of the length of the hydrocarbon chain in the detected hydrocarbons—the carbon chain length mode in a typical diesel fuel is C ₁₆ —the test was terminated when the equivalent of 1000 ppm was found. _C3 . Thus, if 187.5 ppm was detected. C ₁₆ , this was equivalent to 1000 ppm. C ₃ (C ₁₆ is equivalent to 5⅓ x C ₃ ).

After testing at a target inlet temperature of approximately 270°C, the system was again preconditioned at an exhaust gas inlet temperature of 490°C for 10 minutes at a flow rate of 1000 kg/h followed by rapid cooling, and an exotherm test was performed at the second target temperature. , for example approximately 260°C. This cycle was repeated to test the generation of an exothermic effect at given temperatures of approximately 250°C, 240°C and 230°C. The test was stopped when either the composite oxidation catalyst could not generate a stable 600° C. exotherm at the outlet end of the composite oxidation catalyst, or the hydrocarbon slip measured at the outlet of the composite oxidation catalyst exceeded 1000 ppm (C ₃ ).

The results of these tests, carried out for examples 1 and 2, are presented in Table 1 below. It should be understood that the lower the inlet temperature at which a stable exotherm can be achieved with acceptable hydrocarbon slippage, the more preferred the option is. This is due to increased system design flexibility in the sense that filter regeneration can be initiated at a lower exhaust gas intake temperature, i.e. without having to wait until the exhaust gas temperature is high enough under normal operating conditions to initiate filter regeneration, which may occur less frequently during normal operation, and this improves overall fuel economy because it is not necessary to inject as many hydrocarbons as needed to achieve the desired exhaust gas temperature at the outlet of the composite oxidation catalyst.

Table 1

Comparative Example 1 (without barium) Example 2 (barium) Inlet temperature (°C) Overshoot HC (C ₃ ) 270 550 425 260 550 450 250 1000 440 240 1000 320 230 n/a 1000

Table 1 shows that the traditional oxidation catalyst (Example 1) cannot provide a stable exotherm at an inlet temperature of 250°C or lower, while the composite oxidation catalyst according to the invention can provide a stable exotherm at temperatures up to 230°C.

Example 4 Evaluation of the protective layer to prevent phosphorus and/or zinc poisoning of the catalyst. Getting Samples

The catalyst according to the invention having the construction shown in FIG. 5 was used to illustrate the principle of operation of the element-protective layer. A cylindrical flow-through honeycomb monolithic cordierite substrate having a length of 10.5 inches x a diameter of 4 inches was coated with a first layer (6) of a porous oxide catalytic coating containing Pt and Pd in a weight ratio of 2:1 and 80 g ft ^-3 barium, on a powder carrier containing alumina doped with 5 wt.% silicon dioxide, for an axial length of 75% from the inlet end (I), and the second layer (7) of a coating of porous oxide containing only Pt, deposited on a powder carrier of alumina doped with 5 wt.% silicon dioxide (without barium), on the axial length of 50% of the substrate from the outlet end (O). The first zone of the porous oxide catalytic coating was obtained by impregnating the first layer of the porous oxide catalytic coating (6) with a solution of platinum and palladium salts sufficient to provide a mass ratio of Pt and Pd of 1 : 1 by weight per 25% of the axial length of the substrate with an additional total load PGM 50 g ft ^-3 . The total platinum group metal loading of the composite oxidation catalyst was 21 g ft ^-3 and the weight ratio of Pt : Pd was 7 : 5, equivalent to 1.4 : 1. ratio Pt : Pd > 1 : 1.

Three samples were prepared. The first sample was used as a control without any protective layer applied. The second sample had a porous oxide coating consisting of alumina doped with 5 wt.% silica (no platinum group metal) - the same silica-doped alumina used in the first (6) and second (7) layers of the catalytic coating. of porous oxide - and applied over the first zone (1) of the catalytic porous oxide coating with a porous oxide coating load of 0.5 g in ^-3 and a total of 30% of the axial length of the substrate from the inlet end of the substrate (I), i.e. e. 25% of the axial length of the first zone of the porous oxide catalytic coating was completely covered by an outer "protective layer" of the porous oxide coating of silica doped alumina, i. e. 120% of the axial length of the first zone of the porous oxide catalytic coating was covered with an outer porous oxide coating layer. The average pore diameter of alumina doped with 5 wt.% silicon dioxide was about 19 nm.

A third sample was prepared similarly to the second sample, except that the "protective layer" loading of the porous oxide coating of 5 wt % silica doped alumina was 1.0 g in ^-3 .

Each of the three samples was subjected to aging in an oven in air at 650°C for 50 hours.

Example 5 Evaluation of the protective layer to prevent phosphorus and/or zinc poisoning of the catalyst. Sample testing

Three samples of coated substrates, obtained in accordance with example 4, were connected in parallel in a cup of our own design, and the substrates placed in the cup were inserted into the exhaust system of a laboratory-mounted 16-liter heavy-duty diesel engine certified to the standard Euro 2 emissions fueled with MK1 fuel, to which ZDTP fuel additive was mixed at a concentration of 1750 ppm. The substrates were then subjected to engine aging using the following cycle, which was calculated to expose the beaked substrates to a total of 0.5 g ZDTP per liter of catalyst substrate per cycle:

(i) 30 minute "soak" with engine load steady state with substrate inlet temperature of 470°C;

(ii) 15 minute "soak" at steady state motor load with substrate inlet temperature of 210°C, followed by 15 minutes at 250°C inlet temperature, and finally 10 minutes at 325°C inlet temperature ; and

(iii) steps (i) and (ii) were repeated 6 (six) times.

The samples were then removed from the beakers and tested in turn using the motor described in Example 3 according to the following procedure.

The "continuous exotherm" test was carried out as follows. Each catalyst was conditioned at an inlet temperature of 490° C. for 20 minutes, followed by rapid cooling to an inlet temperature of 320° C., at which the catalyst was kept for 10 minutes. Then, the injection of hydrocarbons through the 7th ^injector was started at a rate that allowed an exothermic effect to be provided, creating 600° C. at the outlet of the substrate. This exothermic effect was maintained in a steady state for 5 minutes. Then, a linear decrease in the ignition temperature of the hydrocarbon oxidation catalyst was started by continuously adjusting the engine load to provide an inlet temperature drop of 1° C. per minute at a flow rate of 720 kg/h. The cycle was terminated when the inlet temperature of the downstream particulate filter fell below 425° C. or the 1500 ppm hydrocarbon slip analyzer limit was reached. _C3 .

The porous oxide coating at the first quarter of the length of the substrate, measured from the inlet end of each substrate sample, was analyzed by X-ray fluorescence (XRF) to characterize the elemental composition of the porous oxide coating and phosphorus and zinc poisoning. The degree of poisoning detected was determined relative to zero taken from a scan of the Omnian multi-element reference standard. The results are shown in Table 2 below.

table 2

Sample Phosphorus (wt%) Zinc (wt%) Reference 2.41 0.10 Cover sample 0.5 g/in ³ 2.23 0.11 Cover sample 1.0 g/in ³ 2.29 0.09

Phosphorus poisoning was constant across all three items, and the difference between any two samples was no more than about 8.0%.

One skilled in the art will appreciate that the phosphorus poisoning achieved using the procedure used in this example provides phosphorus poisoning in excess of that experienced in the art during normal operation (see above in this document where the phosphorus poisoning in the catalyst sample at the end its service life was from 1.0 to 1.5 wt.% phosphorus). However, the level of phosphorus poisoning obtained using the procedures described in this example 5 was comparable to the level observed empirically in normal use at the end of the vehicle's life.

The results of tests with a continuous exothermic effect are presented in table 3.

Table 3

Sample End of exotherm (°C) at inlet temperature <500°C 650°C/50 h aging Plus additional aging with ZDTP Reference 232.4 302.8 Cover sample 0.5 g/in ³ 237.2 301.9 Cover sample 1.0 g/in ³ 237.6 270.6

From these results, it can be seen that there was a slight increase in inlet temperature of 5.2°C (2.2%) required to achieve an exothermic effect of ≥500°C for the two samples containing the protective layer element compared to the reference catalyst without a protective layer element. This shows that there is a small and practically negligible increase in inlet temperature at which the engine control can start generating an exothermic effect to regenerate a downstream filter component in an exhaust gas system in accordance with the invention comprising a composite oxidation catalyst including an element - protective layer.

In addition, it can be seen that the sample including the protective layer with a load of 1.0 g/in ³ retained a significantly higher oxidative activity of hydrocarbons compared to the reference (to achieve an exothermic effect of 500°C requires an inlet temperature loss of only 13.9% , compared to a 30.3% inlet temperature loss for the reference sample), despite the same oxidation catalyst segments in the reference and in the sample according to the invention, which have a similar amount of poisonous phosphorus present (see Table 3). However, it can also be seen that the sample having a porous oxide outer coating load of 0.5 g/in ³ had a loss of activity similar to the reference sample.

Example 6 Additional Evaluation of the Protective Layer to Prevent Catalyst Poisoning by Phosphorus and/or Zinc

A catalyst was obtained having a composition and design similar to that of the catalyst described in Example 4, except that the total platinum group metal loading of the composite oxidation catalyst was 15 g ft ^-3 and the Pt:Pd weight ratio was 7.24: 5, which is equivalent to 1.45 : 1, but the Pt : Pd mass ratio in the first porous oxide coating zone was still > 1 : 1.

The following samples were received.

Table 4

Example No. Powder material - metal oxide in protective layer Porous oxide coating load with protective layer (g/in ³ ) Cover, load Pt : Pd (g/ft ³ ) 6.1 Missing (reference) - - 6.2 Gamma aluminum oxide 1.0 - 6.3 Alumina doped with 5 wt% silica 1.0 - 6.4 Alumina doped with 5 wt% silica 1.5 - 6.5 Alumina doped with 30 wt% silica 1.0 - 6.6 "Wide pore alumina" 1.0 - 6.7 Aluminosilicate Zeolite AEI 1.0 - 6.8 Cu-Ion Exchange Aluminosilicate Zeolite AEI 1.0 - 6.9 Cerium oxide 1.5 - 6.10 Alumina doped with 5 wt% silica 1.0 5.0 6.11 Gamma aluminum oxide 1.5 5.0 6.12 Alumina doped with 5 wt% silica 1.5 5.0 6.13 Alumina doped with 5 wt% silica 1.5 10.0 6.14 Alumina doped with 5 wt% silica 1.5 15.0

The fresh "gamma alumina" of Examples 6.2 and 6.11 had a typical average pore diameter of about 13 nm. Fresh "alumina doped with 5 wt.% silicon dioxide" in examples 6.3, 6.4 and 6.10 and 6.12-6.14 inclusive had an intrinsic average pore diameter of 15 nm. Fresh "broad pore alumina" had an intrinsic average pore diameter of about 20 nm. The fresh cerium oxide from Example 6.9 had an intrinsic average pore diameter of about 8 nm. The ratio of silica to alumina in the AEI aluminosilicate zeolite of Examples 6.7 and 6.8 was about 20. The copper load in the Cu-exchanged AEI aluminosilicate zeolite of Example 6.8 was about 3.8% by weight. All of the metal oxide powder materials used in this example had a fresh specific surface area >100 m ² /g.

The metal oxide powder used in each example of the protective layer was ground to obtain a D90 value of <20 μm, a D50 value (average particle size) of <8 μm, the combination, according to the applicant, gives an average pore diameter between particles in the protective layer ≥10 nm .

All samples were aged in an air oven at 650°C for 50 hours. Test examples were carried out in the same manner as described in example 5 above in this document. The results are shown in Table 5 below.

Table 5

Sample End of exotherm (°C) at inlet temperature < 500°C 650°C/50 h aging Plus additional aging with ZDTP 6.1 239.3 285.9 6.2 256.0 269.3 6.3 250.7 272.8 6.4 251.2 265.3 6.5 254.6 271.6 6.6 247.7 266.1 6.7 252.6 272.4 6.8 57.0 276.7 6.9 245.3 273.9 6.10 250.2 262.5 6.11 246.2 265.9 6.12 247.8 263.0 6.13 247.1 260.8 6.14 242.5 254.9

From the results shown in Table 5, it can be seen that all examples coated with a protective layer have a reduced exothermic activity before phosphorus aging compared to the control (reference) example 6.1, where the exothermic termination temperature is 239.0°C. However, all examples 6.2-6.14 inclusive, having a protective layer, showed higher efficiency than the reference sample after phosphorus aging (285.9°C). The most effective examples were those that had a reasonable balance between performance before phosphorus aging, eg <252.0°C, and after phosphorus aging, eg <273.0°C.

In addition, it can be seen that samples with a higher load of porous oxide coating (compare, for example, examples 6.4 and 6.3) showed better performance, as did examples in which PGM was applied to the powdered oxide protective layer material.

Example 7 Study of Delta Between Fresh and Aged Catalyst in NO Oxidation Catalyst Activity with Variation in Porous Oxide Coating Downstream Composition

A number of catalysts were prepared, similar to those described in Example 4, but without the protective layer, and having the design shown in FIG. 5. The only other differences from the catalyst samples of Example 4 were that the total combined platinum group metal loading of the composite oxidation catalyst was 30 g ft ^-3 ; and the composition of the second layer (7) of the porous oxide coating was modified to study the oxidative activity of NO at the outlet zone; details are given in Table 7 below. The total load of platinum group metals in all samples in the second layer of porous oxide coating in this example 7 was 12.5 g ft ^-3 , the load of porous oxide coating in the second layer of porous oxide coating in all samples tested was equivalent, and none of the second porous oxide coating layers tested included barium. The overall weight ratio of Pt : Pd in the composite oxidation catalyst was generally different from that of the samples from Example 4.

Each fresh catalyst was introduced into the test exhaust system of the diesel engine installed on the laboratory bench described in Example 3. The fresh catalyst was first "conditioned" for 30 minutes at engine load and engine speed to provide a catalyst bed temperature of 550°C. The resulting "conditioned" catalyst was then allowed to cool to room temperature. The conditioned fresh catalyst was then tested during a transient load ramp test cycle at a constant engine speed of 1400 rpm and increasing space velocity to determine the NO oxidative activity of the composite oxidation catalyst. The dependence of the detected NO ₂ /NO _x ratio in the exhaust gas downstream from the composite oxidation catalyst on the substrate inlet temperature was recorded. The test catalyst was then cooled, removed from the beaker, and subjected to hydrothermal aging in an oven in an air/10% H ₂ O (steam) atmosphere at 600° C. for 140 hours to simulate oxidative activity at the end of vehicle life. The aged catalyst was then re-installed in the exhaust system of a diesel engine installed on a laboratory bench, re-conditioned and re-tested using the same protocol as described for a fresh catalyst.

Table 7

Sample Heat Resistant Metal Oxide Substrate Material Mass ratio of Pt : Pd (total content of PGM 12.5 g/ft ³ ) Fresh catalyst, NO ₂ /NO _x at 300°C (%) Hydrothermally aged (600°C/140 h) catalyst, NO ₂ /NO _x at 300°C (%) "Delta" (%) between fresh and aged
NO ₂ /NO _x 7.1 Alumina doped with 5 wt% silica ten 64.7 47.6 17.1 7.2 Alumina doped with 5 wt% silica 2:1 54.8 40.4 14.4 7.3 "Preliminary
carefully prepared
fused" alumina doped with 5 wt.% silica with 3.2 wt.% manganese† ten 49.1 42.8 6.3 7.4 Alumina doped with 5 wt% silica + 3.2 wt% manganese† (by impregnation)* ten 50.1 40.3 9.8

†Equivalent to 5.0 wt% MnO ₂ in calcined material.

*Alumina doped with 5 wt.% silica was impregnated with a solution of manganese nitrate at a concentration sufficient to achieve the desired mass of manganese after calcination.

Example 8 Additional Studies of Delta Between Fresh and Aged Catalyst in NO Oxidation Catalyst Activity with Porous Oxide Coating Downstream Composition Change

A number of catalysts were prepared similar to those described in Example 7 and having the design shown in FIG. 5. The only differences from the catalyst samples of Example 7 were that the first zone of porous oxide catalytic coating was obtained by impregnating the first layer of catalytic coating (6) with a solution of platinum and palladium salts sufficient to impregnate 25% of the axial length of the substrate with additional Pt and Pd 35 g ft ^-3 in a 1 : 1 weight ratio such that the total load of platinum group metals is 20 g ft ^-3 in total; and the total load of platinum group metals in all samples in the second layer of porous oxide coating in this example 8 was 7.5 g ft ^-3 . The total mass ratio of Pt : Pd in the composite oxidation catalyst is 1.9 : 1

The tests were carried out in the same manner as described in example 7 upstream, except that the aging of the catalyst was different. In this Example 8, the fresh "conditioned" catalyst was aged in an air oven at 650° C. for 50 hours.

Table 8

Sample Heat Resistant Metal Oxide Substrate Material Fresh catalyst, NO ₂ /NOx at 300 °C (%) Aged (650°C/50h) catalyst, NO ₂ /NOx at 300°C (%) "Delta" (%) between fresh and aged NO ₂ /NOx 8.1 Alumina doped with 5 wt% silica 60.2 41.4 18.8 8.2 "Prefabricated" alumina doped with 5 wt% silica with 3.2 wt% manganese 52.1 32.8 19.3 8.3 Mixed magnesium aluminum oxide containing 3.5 wt% Mg† 56.9 39.2 17.7 8.4 “Pre-cooked” doped with 0.64 wt.% manganese* ¹ mixed magnesium-alumina containing 3.5 wt.% Mg† 51.9 37.8 14.0 8.5 "Pre-cooked" doped 1.9 wt.% manganese* ² mixed magnesium-alumina containing 3.5 wt.% Mg† 51.3 36.4 14.9 8.6 "Pre-cooked" doped with 3.2 wt.% manganese* ³ mixed magnesium-alumina containing 3.5 wt.% Mg† 47.1 34.7 12.4

† Equivalent to 5.7 wt% MgO/94.3 wt% Al ₂ O ₃ . The material is predominantly a single cubic phase spinel as determined by X-ray diffraction (XRD). Some excess Al ₂ O ₃ may be present.

* ¹ Equivalent to 1.0 wt.% MnO ₂ .

* ² Equivalent to 3.0 wt.% MnO ₂ .

* ³ Equivalent to 5.0 wt.% MnO ₂ .

In addition, the composite oxidation catalysts of the present Example 8 were tested in the "continuous exotherm" test described in Example 5, but without ZDTP aging. The results are presented in the following table 9.

Table 9

Sample Temperature (°C) at the inlet of the catalyst aged at 650°C/50 hours, termination of the exotherm at an inlet temperature <500°C 8.1 246.2 8.2 240.6 8.3 235.7 8.4 238.4 8.5 238.7 8.6 237.0

From the results shown in Tables 8 and 9, samples 8.4, 8.5, and 8.6, including preformed manganese-doped mixed substoichiometric alumina magnesium oxides, exhibit an unexpected and beneficial combination of a reduced ratio of fresh to aged catalyst activities in terms of NO oxidative activity, and also improved formation of the exothermic effect.

Example 9 Study of the Pt : Pd Mass Ratio in the First Zone of a Porous Oxide Catalytic Coating

The current value of palladium by weight is more than twice that of platinum. In this example 9, the Applicant performed a series of experiments to reduce the total content of palladium in the composite oxidation catalyst in accordance with the invention.

A number of catalysts were prepared similar to those described in Example 8 and having the design shown in FIG. 5. The only difference from the catalyst samples of Example 8 was that the composition of the impregnation solution for the first zone of the porous oxide catalytic coating was varied so as to achieve the range of mass ratios Pt : Pd given in Table 10 below, over 25% of the axial length of the substrate from the inlet end of the support at an additional total PGM load of 35 g ft ^-3 , and the overall oxidation catalyst composite had a total platinum group metal load of 15 g ft ^-3 ; and the only platinum group metal in the second porous oxide coating layer was platinum, i.e. the weight ratio of Pt : Pd was 1 : 0 with a porous oxide coating load of 2.0 g ft ^-3 .

Table 10 shows the results of the "continuous exotherm" test of catalyst samples aged and tested as described in Example 8.

Table 10

Sample Mass ratio of Pt : Pd in the first zone of the porous oxide catalytic coating Overall Pt : Pd Ratio in the Composite Oxidation Catalyst Temperature (°C) at the inlet of the catalyst aged at 650°C/50 hours, exothermic termination at inlet temperature < 500°C 9.1 eleven 1.45:1 258 9.2 2:1 2.21:1 256 9.3 3:1 2.8:1 260 9.4 4:1 3.28:1 262 9.5 ten 7.55:1 280

From the results shown in Table 10, it can be seen that the weight ratio of platinum to palladium in the first zone of the porous oxide catalytic coating can be increased without unduly affecting the ability of the oxidation catalyst composite to generate and maintain an exothermic effect. However, if the impregnation medium for the first zone of the porous oxide catalytic coating does not contain palladium (Example 9.5), the exothermic effect fails the test, so this configuration is less preferred. Accordingly, it is preferred that the combined Pt : Pd weight ratio of the impregnating medium and the underlying impregnated porous oxide catalytic coating contain some palladium to stabilize the platinum, for example in a ratio of 10 : 1 ≥ 1 : 1.

For the avoidance of doubt, the entire contents of all documents cited herein are incorporated herein by reference.

Claims (25)

1. Composite oxidation catalyst (14, 16, 18, 20) for use in an exhaust system for purifying exhaust gas produced by an internal combustion engine (30) for a compression ignition vehicle, and located upstream in the exhaust system flow relative to the particulate filter substrate (44, 50), wherein the composite oxidation catalyst comprises: a substrate (5) having an overall length L and a longitudinal axis and having a substrate surface extending in the axial direction between the first end (I) of the substrate and the second end (O) of the substrate; and three or more zones (1, 2, 3 or 1, 2, 3, 4) of the porous oxide catalytic coating, located sequentially in the axial direction on the surface of the substrate and along it, while the first zone (1) of the porous oxide catalytic coating, having a length L ₁ , and L ₁ <L, is formed at one end by the first end (I) of the substrate, and at the second end by the first end (19, 21) of the second zone (2) of the catalytic coating of porous oxide with a length of L ₂ , when this L ₂ <L, and the first zone (1) of the porous oxide catalytic coating contains the first material-substrate of a heat-resistant metal oxide and two or more components deposited on it, representing a platinum group metal, containing both platinum and palladium at a mass the ratio of platinum and palladium ≥1; the second zone (2) of the porous oxide catalytic coating contains a second material-substrate of a heat-resistant metal oxide and one or more components deposited on it, which is a platinum group metal, and the third zone (3) of the porous oxide catalytic coating containing the third material - a refractory metal oxide substrate and one or more platinum group metal components deposited thereon is formed at its second end by a second end (O) of the substrate, while the total load of platinum group metals in the first zone (1) of the porous oxide catalytic coating, expressed in grams of platinum group metal per liter of substrate volume (g/l), is greater than the total load of platinum group metals in the second zone (2) of the catalytic coating of porous oxide, and the total load of platinum group metals in the third zone (3) of the porous oxide catalytic coating, expressed in grams of platinum group metal per liter of support volume (g/l), is less than the total load of platinum group metals in the second zone (2) of the catalytic porous oxide coating, wherein the first zone (1) of the catalytic porous oxide coating comprises one or more first alkaline earth metal components deposited on a first heat resistant metal oxide substrate material. 2. Composite oxidation catalyst according to claim 1, containing four zones (1, 2, 3, 4) of the catalytic coating of porous oxide, and the fourth zone (4) of the catalytic coating of porous oxide is located between the second zone (2) of the catalytic coating of porous oxide and a third zone (3) of the porous oxide catalytic coating, wherein the fourth zone (4) of the porous oxide catalytic coating comprises a fourth heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, and formed by the second end of the second zone of the porous oxide catalytic coating at the first end (23), and at the second end (17) by the first end of the third zone (3) of the porous oxide catalytic coating, and the total load of platinum group metals in the fourth zone ( 4) porous oxide catalytic coating, expressed as grams of platinum group metal per liter of support volume (g/l), more generally and platinum group metal loads in each of the second zone (2) of the porous oxide catalytic coating and the third zone (3) of the porous oxide catalytic coating. 3. Composite oxidation catalyst according to claim 2, comprising a first layer (6) of a porous oxide catalytic coating and a second layer (7) of a porous oxide catalytic coating, wherein the first layer (6) of the porous oxide catalytic coating contains a substrate material of heat-resistant the metal oxide and one or more platinum group metal components deposited thereon has a length L ₃ , with L ₃ <L, and is formed at one end by the first end (I) of the substrate; and the second layer (7) of the porous oxide catalytic coating comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components deposited thereon, has a length L ₄ , with L ₄ <L, and is formed at the second end the second end (O) of the substrate, wherein the fourth zone (4) of the catalytic coating of porous oxide contains a two-layer region of overlap of the first layer (6) of the catalytic coating of porous oxide and the second layer (7) of the catalytic coating of porous oxide, and the third zone (3) the porous oxide catalytic coating comprises one layer of the second porous oxide catalytic coating layer (7) which is not formed from the overlap region. 4. A composite oxidation catalyst according to any one of the preceding claims, wherein the total load of platinum group metals in the first zone (1) of the porous oxide catalytic coating is <3.53 g/l (<100 g/ft ³ ) in terms of elemental metal . 5. The composite oxidation catalyst according to any one of the preceding claims, wherein the weight ratio of platinum to palladium in the first zone (1) of the porous oxide catalytic coating is 10:1≥1.5:1. 6. A composite oxidation catalyst according to any one of the preceding claims, having a total load of platinum group metals on the support (5) in total from 0.18 to 2.19 g/l (5-60 g/ft ³ ) in terms of elemental metal. 7. The composite oxidation catalyst according to any one of the preceding claims, wherein the total weight ratio of Pt:Pd in the composite oxidation catalyst (14, 16, 18, 20) is generally 3:2 to 9:1. 8. The composite oxidation catalyst according to any one of the preceding claims, wherein the weight ratio of platinum to palladium in each successive zone (1, 2, 3; or 1, 2, 3, 4) of the porous oxide catalytic coating arranged in series along the length L of the substrate after the first zone (1) of the porous oxide catalytic coating, more than in the immediately preceding zone of the porous oxide catalytic coating. 9. Composite oxidation catalyst according to any one of the preceding claims, wherein the total load of alkaline earth metals in the first zone (1) of the porous oxide catalytic coating is from 0.35 to 3.53 g/l (10-100 g/ft ³ ) in calculation for elemental metal. 10. The composite oxidation catalyst according to any one of the preceding claims, wherein the weight ratio of total elemental alkaline earth metal to total elemental platinum group metal in the first zone (1) of the porous oxide catalytic coating is <1:1. 11. The composite oxidation catalyst according to any one of the preceding claims, wherein the first zone (1) of the porous oxide catalytic coating has an uneven distribution of one or more platinum group metal components and/or one or more first alkaline earth metal components. , in the direction perpendicular to the surface of the substrate (5), according to electron probe microanalysis (EPMA), wherein the concentration of one or more platinum group metal components and/or the first alkaline earth metal component decreases in the direction perpendicular to substrate surface. 12. A composite oxidation catalyst according to any one of the preceding claims, wherein at least the first refractory metal oxide support material comprises alumina doped with a heteroatom, preferably silica. 13. The composite oxidation catalyst according to any one of the preceding claims, wherein the third zone (3) of the catalytic porous oxide coating contains manganese and/or the second layer (7) of the catalytic porous oxide coating contains manganese. 14. The composite oxidation catalyst according to any one of the preceding claims, comprising an outer layer (G) of the porous oxide coating extending axially from the first end (I) of the substrate to protect at least a portion of the underlying first zone (1) of the porous oxide coating from phosphorus and/or zinc poisoning during operation, wherein the outer layer (G) of the porous oxide coating has a powder metal oxide load of >48.8 g/l (>0.8 g/in ³ ) and optionally contains a platinum group metal. 15. Compression ignition internal combustion engine (30) for a heavy duty diesel vehicle, comprising an exhaust system (32), the exhaust system comprising a composite oxidation catalyst (42) according to any one of the preceding claims. and a particulate filter substrate (44, 50) located downstream of the oxidation catalyst, wherein the first end of the composite oxidation catalyst substrate (14, 16, 18, 20) is oriented upstream. 16. The use of a composite catalyst (14, 16, 18, 20) oxidation according to any one of paragraphs. 1-14 to heat the particulate filter substrate (44, 50) located downstream of the composite oxidation catalyst in the exhaust system (32) of an internal combustion engine for a compression ignition vehicle. 17. The method of obtaining a composite oxidation catalyst according to any one of paragraphs. 1-14, including stages: (a) applying a porous oxide catalytic coating layer (6) to the substrate surface from one end (I, O) of the substrate (5) to a length less than the total length of the substrate, wherein the porous oxide catalytic coating layer (6) comprises a substrate material of a heat-resistant metal oxide; and one or more platinum group metal components; and (b) impregnating the porous oxide catalytic coating layer (6) in a zone of length L ₁ formed at one end by the first end (I) of the substrate with a solution containing one or more platinum group metals, wherein one or more alkaline earth metal components are present in the porous oxide catalytic coating layer (6) in step (a) and/or in the impregnation solution used in step (b), the method further comprising step (a' ) before step (a) or after step (a), but in any case before step (b) of applying a second layer of catalytic coating of porous oxide to the substrate from the second end of the substrate to a length less than the total length of the substrate so that the first layer of catalytic coating of porous oxide coating partially overlapped the second porous oxide catalytic coating layer or the second porous oxide catalytic coating layer partially overlapped the first porous oxide catalytic coating layer, wherein the second porous oxide catalytic coating layer comprises a heat-resistant metal oxide substrate material and one or more platinum group metal components. 18. The composite oxidation catalyst of claim 1, wherein the internal combustion engine for the compression ignition vehicle is a heavy duty diesel engine. 19. Composite oxidation catalyst according to claim 1, wherein the support is a flow-through monolith of the support with a honeycomb structure.

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