CN110681377A

CN110681377A - Diesel oxidation catalyst composites

Info

Publication number: CN110681377A
Application number: CN201910981517.6A
Authority: CN
Inventors: S·孙; S·A·罗斯; C·文特; S·斯蒂贝尔斯; H·德林
Original assignee: BASF Corp
Current assignee: BASF Corp
Priority date: 2013-08-28
Filing date: 2013-08-28
Publication date: 2020-01-14
Also published as: CN104703677A

Abstract

The invention discloses methods and compositions for treating exhaust emissions, such as reducing unburned Hydrocarbons (HC) and carbon monoxide (CO) and oxidizing NO to NO₂The oxidation catalyst composite of (1). The catalyst composite includes two washcoat layers containing two different platinum group metal compositions to optimize NO exiting the catalyst composite₂. The key to improving NO oxidation is to have a catalyst layer that contains Pt and is substantially free of Pd. Methods and systems for utilizing the catalyst composites are also disclosed.

Description

Diesel oxidation catalyst composites

The application is a divisional application of patent application with the application number of 201380052815.8, the application date of 2013, 8 and 28 and the invention name of "diesel oxidation catalyst composite".

Technical Field

The present invention relates generally to layered catalysts for treating gaseous streams containing hydrocarbons, carbon monoxide and nitrogen oxides. More particularly, the present invention relates to lean burn oxidation catalyst composites having multiple layers (e.g., two layers) of material.

Background

The operation of lean-burn engines, such as diesel engines and lean-burn gasoline engines, provides users with excellent fuel economy and very low emissions of gas phase hydrocarbons and carbon monoxide due to their operation at high air/fuel ratios under lean conditions. The emissions from lean burn engines include Particulate Matter (PM), Nitrogen Oxides (NO)_x) Unburned Hydrocarbons (HC) and carbon monoxide (CO). NO_xAre terms used to describe various chemical classes of nitrogen oxides, including Nitric Oxide (NO) and nitrogen dioxide (NO)₂) And so on.

Oxidation catalysts comprising noble metals dispersed on refractory metal oxide supports are known for treating exhaust gases of diesel engines to convert hydrocarbon and carbon monoxide gaseous pollutants by catalyzing the oxidation reaction of these pollutants to carbon dioxide and water. Such catalysts are typically housed in a unit called a Diesel Oxidation Catalyst (DOC), or more simply a catalytic converter, which is placed in the exhaust flow path from the diesel powered engine to treat the exhaust before it is exhausted to the atmosphere. Typically, the diesel oxidation catalyst is formed on a ceramic or metal substrate support (such as a flow-through monolith support, as described below) on which one or more catalyst coating compositions are deposited. In addition to converting gaseous HC, CO and particulates, an oxidation catalyst containing a platinum group metal (which is typically dispersed on a refractory oxide support) promotes the conversion of Nitric Oxide (NO) to NO₂And (4) transformation.

An important factor in DOC design is catalyst deactivation after high temperature exposure. Thermally induced DOC passivation may occur as a result of catalytic component or support sintering. Sintering of the catalytic component involves coalescence or crystallite growth of the initially well-dispersed catalytic sites. This aggregation results in a loss of surface to volume ratio, thereby reducing catalytic performance. Alternatively, exposure of the DOC to high temperatures may cause the catalyst support to sinter. This involves a loss of the pore structure of the support, resulting in a loss of accessibility to the catalytically active sites.

As emissions regulations become more stringent, there is a continuing need to develop compounds that provide improved performance (e.g., NO at modified DOCs)₂Formed) to improve the overall performance of a lean burn engine exhaust system.

Disclosure of Invention

Aspects of the invention include diesel oxidation catalyst compositions, methods, and systems for treating exhaust gas from lean-burn engines. Embodiments of the invention may be used for, but are not limited to, converting NO from engine exhaust_xCO and HC. One aspect of the invention relates to an oxidation catalyst for reducing exhaust emissions from a lean burn engine comprising a support substrate having a length, an inlet end and an outlet end, an oxidation catalyst catalytic material on the support, the oxidation catalyst catalytic material comprising a lower washcoat layer (washcoat) and an upper washcoat layer. The lower wash coat comprising a platinum (Pt) component and a palladium (Pd) component, the Pt to Pd weight ratio being in the range of about 4:1 to 1: 4; the upper washcoat layer comprises zeolite, Pt, and a refractory metal oxide support, the upper washcoat layer being substantially free of palladium. The oxidation catalyst composite of this aspect of the invention is effective in reducing hydrocarbons and carbon monoxide and is also effective in oxidizing NO in lean burn engines to NO₂. In some embodiments, the upper washcoat layer is substantially free of barium and the lower washcoat layer is substantially free of zeolite. In other embodiments, the refractory metal oxide support comprises silica-alumina. The upper washcoat layer of various embodiments includes the Pt component in an amount of about 10g/ft³To 120g/ft³Within the range. In one or more other embodiments, the lower washcoat layer comprises a Pt component in an amount of about 5g/ft³To 85g/ft³Pd group within and includedThe amount of component is about 5g/ft³To 50g/ft³Within the range. In some embodiments, the upper washcoat layer contains a higher loading of platinum group metals than the lower washcoat layer in order to maximize NO oxidation. In other embodiments, the composite contains a platinum group metal in the upper layer in a weight ratio in the range of 1:1 to 4:1 relative to that in the lower layer. In other embodiments, the upper washcoat layer comprises platinum at about 60 to 120g/ft³And the lower cladding layer comprises a weight ratio of platinum to palladium in a range of about 1:4 to 1: 1. In one or more embodiments, the oxidation catalyst is adapted to maximize CO and HC oxidation, wherein the upper washcoat layer contains a lower platinum group metal loading than the lower washcoat layer. In various embodiments, the composite contains a platinum group metal in the upper layer in a weight ratio in the range of 1:4 to 1:1 relative to that in the lower layer to promote oxidation of hydrocarbons and carbon monoxide while also providing at least 30% NO oxidation. In some embodiments, the upper washcoat layer comprises platinum at about 10 to 60g/ft³And the lower washcoat layer comprises a ratio of platinum to palladium in a range of about 1:1 to 4:1 platinum to palladium by weight.

In one or more embodiments, the present invention is directed to an oxidation catalyst composite for reducing exhaust gas emissions from a lean burn engine comprising a support substrate having a length, an inlet end and an outlet end, an oxidation catalyst catalytic material on the support, the oxidation catalyst catalytic material comprising a lower washcoat layer and an upper washcoat layer. The lower washcoat layer comprises a refractory metal oxide support, a platinum (Pt) component, and a palladium (Pd) component, with a Pt to Pd weight ratio in a range of about 9:1 to 1: 4. The upper washcoat layer comprises zeolite, a refractory metal oxide support, a platinum component (Pt), and a palladium component (Pd), with a Pt to Pd weight ratio in a range of about 1:1 to 100: 1. The oxidation catalyst composite is effective in reducing hydrocarbons and carbon monoxide, and oxidizing NO in lean burn engine exhaust to NO₂. In some embodiments, the top washcoat layer further comprises a concentration in the range of about 3 to 30g/ft³Barium oxide within the range. In various embodiments, the top washcoat layer contains a lower platinum group metal loading than the platinum group metal loadingThe lower washcoat layer to maximize CO and HC oxidation.

In one or more embodiments, the present invention is directed to a catalyst composite for reducing exhaust emissions of a lean burn engine comprising a support substrate having a length, an inlet end and an outlet end, an oxidation catalyst catalytic material on the support, the oxidation catalyst catalytic material comprising a lower washcoat layer and an upper washcoat layer. The upper washcoat layer comprises a refractory metal oxide, a zeolite, and a platinum component (Pt) and a palladium component (Pd) in a Pt to Pd weight ratio in a range of about 9:1 to 1: 4. The undercushion layer comprises Pt and a refractory metal oxide support, and the oxidation catalyst composite is effective for reducing hydrocarbons and carbon monoxide and oxidizing NO in lean burn engine exhaust to NO₂. In various embodiments, the lower cladding layer is substantially free of palladium and substantially free of barium. In some embodiments, the lower washcoat layer further comprises a palladium component, the platinum component being present in a Pt to Pd weight ratio with respect to the palladium component in a range of about 1:1 to 100: 1. In other embodiments, the lower cladding layer is further comprised at about 3-30g/ft³Barium oxide within the range.

Another aspect of the invention relates to a method of treating an exhaust gas from a lean burn engine, the method comprising flowing the exhaust gas through a honeycomb substrate comprising a lower washcoat layer comprising a platinum (Pt) component and a palladium (Pd) component, the Pt to Pd weight ratio being in a range of about 4:1 to 1: 4; and an upper washcoat layer comprising zeolite, Pt, and a refractory metal oxide support, the upper washcoat layer being substantially free of palladium, wherein the diesel oxidation catalyst is effective to reduce CO and HC and oxidize NO from the exhaust stream to NO₂. In various embodiments, the upper washcoat layer of the oxidation catalyst composite is substantially free of Ba and the lower washcoat layer is substantially free of zeolite. In one or more embodiments, the refractory metal oxide support comprises silica-alumina.

Another aspect of the invention relates to a system for treating lean burn engine exhaust emissions comprising hydrocarbons, carbon monoxide, and other exhaust gas components. The emissions treatment system includes an exhaust conduit in fluid communication with a lean burn engine via an exhaust manifold; the oxidation catalyst composite of one or more embodiments of the present invention, wherein the support is a flow-through substrate or a wall-flow substrate; and a catalyzed soot filter and an SCR catalyst composition are located downstream of the oxidation catalyst composite. In one or more embodiments, the SCR catalyst composition is supported on the catalyzed soot filter. In some embodiments, the SCR catalyst composition comprises a copper-promoted small pore zeolite having 8-membered ring openings. In other embodiments, the small pore zeolite has the CHA structure.

Brief Description of Drawings

FIG. 1 is a perspective view of a honeycomb-type refractory support member that may contain a novel Diesel Oxidation Catalyst (DOC) washcoat composition in accordance with the present invention;

FIG. 2 is a partial cross-sectional view enlarged relative to FIG. 1 and taken in a plane parallel to the end face of the carrier of FIG. 1, showing an enlarged view of one of the gas flow channels shown in FIG. 1;

FIG. 3 is a schematic illustration of an engine emissions treatment system according to an embodiment of the present invention;

FIG. 4 is a schematic illustration of an engine treatment system according to an embodiment of the present disclosure; and is

FIG. 5 is a schematic diagram of an engine treatment system according to an embodiment of the present invention.

Detailed Description

Lean burn (e.g., diesel) catalyst composites, systems, and methods are provided. In one or more embodiments, the catalyst composite comprises two washcoat layers: a lower washcoat layer comprising platinum and palladium and a refractory metal oxide support; and an upper washcoat layer comprising zeolite, platinum, and a refractory metal oxide support. In one or more embodiments, the upper washcoat layer is substantially free of palladium. Providing a separate washcoat layer is intended to increase NO without excessive loss of CO conversion₂And (4) forming. It has been found that minimizing and/or eliminating palladium in the washcoat layer enhances the aged catalyst composite that experiences aging when placed in the exhaust system of a lean burn engineNO in the feed₂And (4) forming. Additionally, varying the ratio of platinum to palladium in the undercoat of catalytic material may further enhance NO in the aged catalyst composite₂While minimizing CO and HC conversion losses.

Another aspect of the invention provides a method for treating lean burn engine exhaust stream emissions containing unburned Hydrocarbons (HC) and carbon monoxide (CO). The catalyst composites described herein may be used to treat an exhaust stream from a diesel engine and increase NO in the exhaust exiting the catalyst composites₂And (4) content.

According to an embodiment of the invention, each layer of the catalyst composite has a different platinum group metal composition. Platinum is essentially the only platinum group metal present in the first layer (first or upper washcoat layer) while both Pt and Pd are present in the second layer (second or lower washcoat layer). The large amount of Pt in the top-wash coat improves sulfur tolerance while enhancing NO₂And (4) forming. The upper washcoat layer contains Hydrocarbon (HC) storage components, such as zeolites, to store HC during cold start of the drive cycle. After warming up the catalyst, the Hydrocarbon (HC) storage component will release the stored HC, which is subsequently converted on the catalyst. In some embodiments, the upper cladding layer is substantially free of barium or NO_xThe compound is stored. In embodiments where barium is present in the overlayer, the barium oxide can be present in an amount between about 3 and 30g/ft³In the meantime. According to one or more embodiments, the upper washcoat layer contains Pt in an amount of about 10 to 140g/ft³In the range, and in specific embodiments, from about 10 to 100g/ft³Within the range.

The second or lower washcoat layer may contain Pt and Pd. In one or more embodiments, the lower washcoat layer has a Pt to Pd weight ratio of less than about 10:1, but greater than about 1:4, for example in the range of about 4:1 to 1: 4. Further, Pt to Pd ratios of about 1:4, about 1:1, or about 2.5:1 and 9:1 are exemplified. In a specific embodiment, a minimum washcoat Pt to Pd weight ratio of 2.5:1 is provided to allow NO to pass₂Formation is maximized while minimizing CO conversion losses. In some embodiments, the lower washcoat layer does not contain any HC storage material(e.g., zeolite) to prevent sintering of PGM on the zeolite. In some embodiments, the lower washcoat layer contains barium to stabilize the silica-alumina washcoat layer against high temperature aging.

Reference to a catalyst composite is meant to include a catalyst having one or more catalyst particles containing a catalyst effective to catalyze HC, CO and/or NO_xA washcoat of an oxidized catalytic component (e.g., a platinum group metal component), such as a honeycomb substrate.

References to "substantially free", "substantially free" and "substantially free" mean that the material may be intentionally provided in the layer in small amounts (i.e., < 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or even 1% by weight of the washcoat) or unintentionally migrate/diffuse to the layer.

Reference to "substantially free of palladium" means that small amounts (i.e., < 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or even 1% by weight of the platinum group metal in the washcoat layer) of the material may be intentionally or unintentionally present in the layer. Reference to "substantially free of barium" means that small amounts (i.e. < 2% by weight of the washcoat) of the material may be present in the layer, intentionally or unintentionally.

Reference to dry weight percent of platinum group metal (e.g., "about 2.8%" on a dry weight basis) refers to the fraction of platinum group metal on the refractory metal oxide support.

By high surface area refractory metal oxide support is meant having a surface area greater thanAnd a wider pore distribution of the support particles. As defined herein, such metal oxide supports do not include molecular sieves, in particular, zeolites. High surface area refractory metal oxide supports, for example, silica-alumina support materials, also known as "silica-alumina oxides," typically exhibit over 60 square meters per gram ("m²In g'), frequently up to about 200m²BET surface area in g or higher. Such silica-alumina is generallyA mixture of gamma and delta phases comprising alumina, but may also contain significant amounts of eta, kappa and theta alumina phases. Refractory metal oxides other than activated alumina may be used as a support for at least some of the catalytic components in a given catalyst. For example, bulk ceria, zirconia, silica zirconia, alpha alumina, titania, silica titania, and other materials are known for such use. While many of these materials suffer from the disadvantage of having a BET surface area significantly lower than activated alumina, this disadvantage tends to be offset by the greater durability of the resulting catalyst. The general meaning of "BET surface area" is for the passage of N₂Adsorption surface area determination by Brunauer, Emmett, Teller method. BET type N may also be used₂Adsorption was used to determine pore diameter and pore volume. Desirably, the activated alumina has a specific surface area of 60 to 350m²A,/g, and typically from 90 to 250m²(ii) in terms of/g. The washcoat loading of the refractory oxide support as a whole is preferably about 0.1 to 6g/in³More preferably about 2 to about 5g/in³And most preferably from about 2 to about 4g/in³。

As used herein, a molecular sieve such as a zeolite refers to a material in the form of particles that can support a catalytic platinum group metal, the material having a substantially uniform pore distribution with an average pore size of no greater than

Reference to a "non-zeolitic support" in a catalyst layer refers to a material that is not a molecular sieve or zeolite and that receives a noble metal, stabilizer, promoter, binder, etc., by association, dispersion, impregnation, or other suitable method. Examples of such supports include, but are not limited to, high surface area refractory metal oxides. One or more embodiments of the present invention include a high surface area refractory metal oxide support comprising an active compound selected from the group consisting of: alumina, zirconia, silica, titania, silica-alumina, zirconia-alumina, titania-alumina, lanthana-zirconia-aluminaBarium oxide-alumina, barium oxide-lanthanum oxide-neodymium oxide-alumina, zirconium oxide-silica, titanium dioxide-silica, and zirconium oxide-titanium dioxide.

The zeolite can be a natural or synthetic zeolite such as faujasite, chabazite, clinoptilolite, mordenite, silicalite, zeolite X, zeolite Y, ultrastable zeolite Y, ZSM-5 zeolite, ZSM-12 zeolite, SSZ-13 zeolite, SAPO5 zeolite, offretite, H beta zeolite, or beta zeolite. The specific zeolite adsorption material has a high silica-alumina ratio. Zeolites can have a silica to alumina molar ratio of at least about 25/1, preferably at least about 50/1, with useful ranges of about 25/1 to 1000/1, 50/1 to 500/1, and about 25/1 to 300/1, about 100/1 to 250/1, or alternatively, about 35/1 to 180/1 is also exemplified. Preferred zeolites include ZSM-5, Y and beta zeolites. Particularly preferred adsorbents may include beta zeolite of the type disclosed in US 6,171,556. The overall zeolite loading should not be less than 0.1g/in³To ensure sufficient HC storage capacity and to prevent premature release of stored petroleum hydrocarbons during the exotherm following low temperature storage. Preferably, the zeolite content is from about 0.4 to about 0.7g/in³Within the range. Premature release of aromatics and petroleum hydrocarbons from zeolites can cause delayed CO and HC light-off.

Reference to "impregnation" refers to placing a noble metal-containing solution into the pores of a material such as a zeolite or non-zeolite support. In a detailed embodiment, the noble metal impregnation is achieved by incipient wetness, wherein the volume of the noble metal-containing dilute solution is approximately equal to the pore volume of the support. Incipient wetness typically results in a substantially uniform distribution of the precursor solution throughout the pore system of the material. Other methods of adding noble metals are also known in the art and may be used.

Details of the components of the gas treatment articles and systems according to embodiments of the invention are provided below.

Carrier

According to one or more embodiments, the support may be any of those typically used to prepare DOC catalysts, and will preferably comprise a metal or ceramic honeycomb structure. Any suitable carrier may be employed, such as a monolithic carrier of the type having a plurality of thin parallel gas flow passages extending through the carrier from an inlet or outlet face thereof, thereby opening the passages to fluid flow therethrough. The channels are essentially straight paths from their fluid inlets to their fluid outlets, defined by walls on which the catalytic material is coated as a "washcoat" such that the gases flowing through the channels contact the catalytic material. The fluid channels of the monolithic carrier are thin-walled channels that may have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like.

Such monolithic supports may contain as many as about 900 or more fluid channels (or "cells") per square inch of cross-section, but much fewer fluid channels may be used. For example, the carrier may have about 50 to 600, more typically about 200 to 400 cells per square inch ("cpsi"). The cells may have a cross-section that is rectangular, square, circular, elliptical, triangular, hexagonal, or has other polygonal shapes. Flow-through substrates typically have a wall thickness of between 0.002 and 0.1 inch. The preferred flow-through substrate has a wall thickness of between 0.002 and 0.015 inches.

The ceramic support may be made from any suitable refractory material, such as cordierite, cordierite-alpha alumina, silicon nitride, silicon carbide, zircon mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, alpha alumina, aluminosilicates, and the like.

The support useful in the layered catalyst composites of the present invention may also be metallic in nature and composed of one or more metals or metal alloys. Various shapes of metal support may be used, such as corrugated sheet or monolithic form. Preferred metal supports include heat resistant metals and metal alloys such as titanium and stainless steel and other alloys with iron as the essential or major component. Such alloys may contain one or more of nickel, chromium and/or aluminium, and the total amount of these metals preferably constitutes at least 15% by weight of the alloy, for example 10-25% by weight chromium, 3-8% by weight aluminium and up to 20% by weight nickel. The alloy may also contain small or trace amounts of one or more other metals such as manganese, copper, vanadium, titanium, and the like. The surface of the aluminum-containing metal support may be oxidized at high temperatures (e.g., 1000 ℃ and higher) to improve the corrosion resistance of the alloy by forming an aluminum oxide layer on the surface of the support. Such high temperature induced oxidation can enhance the adhesion of the refractory metal oxide support and the catalytically promoting metal component to the support.

For Catalyzed Soot Filters (CSF), the substrate may be a honeycomb wall flow filter, wound or filled fiber filter, open cell foam, sintered metal filter, or the like, with wall flow filters being preferred. Wall flow substrates useful for supporting CSF compositions have a plurality of substantially parallel fine gas flow channels extending along the longitudinal axis of the substrate. Typically, each channel is blocked at one end of the substrate body, with alternate channels being blocked on opposite end faces.

Particular wall flow substrates for use in the system of the present invention include thin porous wall honeycombs (monoliths) through which the fluid flow passes without greatly increasing the back pressure or pressure drop across the article. Normally, the presence of a clean wall flow type article will produce a back pressure of 0.036psi to 10 psi. The ceramic wall flow type substrate used in the system is preferably formed of a material having a porosity of at least 40% (e.g., 40% to 70%) and having an average pore size of at least 5 microns (e.g., 5 to 30 microns). More preferably, the substrate has a porosity of at least 46% and has an average pore size of at least 10 microns. When substrates having these porosities and these average pore sizes are coated using the techniques described below, a sufficient level of loading of CSF catalyst composition onto the substrate can be achieved to achieve good NO_xConversion efficiency and burning off of soot. These substrates are capable of retaining sufficient exhaust flow characteristics, i.e., acceptable back pressure, despite CSF catalyst loading. Suitable wall-flow substrates are disclosed, for example, in US 4,329,162.

Fig. 1 and 2. Fig. 1 and 2 show an exemplary carrier member 2 according to an embodiment of the present invention. Referring to fig. 1, refractory carrier member 2 is cylindrical having a cylindrical outer surface 4, an upstream end face 6, and a downstream end face 8 identical to end face 6. The carrier member 2 has a plurality of parallel fine airflow channels 10 formed therein. As can be seen in fig. 2, the fluid passages 10 are formed by walls 12 and extend through the carrier 2 from the upstream end face 6 to the downstream end face 8, said passages 10 being unobstructed so as to allow fluid (e.g. gas flow) to pass longitudinally through the carrier 2 via its gas flow passages 10. As can be more readily seen in fig. 2, the walls 12 are so dimensioned and configured that the gas flow channels 10 have a substantially regular polygonal shape, substantially square in the illustrated embodiment, but with rounded corners, according to U.S. patent No. 4,335,023 to j.c. dettling et al, 6/15, 1982. The discrete under layer 14 is referred to in the art and sometimes hereinafter as a "wash coat" and is adhered or coated onto the wall 12 of the carrier member. As shown in fig. 2, a second discrete upper washcoat layer 16 is coated on the lower washcoat layer 14.

As shown in fig. 2, the carrier member comprises void spaces provided by the gas flow channels 10, and the cross-sectional area of these channels 10 and the thickness of the walls 12 bounding said channels will vary depending on the type of carrier member. Similarly, the weight of the washcoat applied to these carriers will vary as appropriate. Thus, in describing the amount of washcoat or catalytic metal component or other component of the composition, it is convenient to use the weight per unit of component per volume of catalyst support. Thus, the unit grams per cubic inch ("g/in") is used herein³") and grams per cubic foot (" g/ft ")³") means the weight of the component per volume of the carrier member (including the volume of void space of the carrier member).

During operation, exhaust gas emissions from lean burn engines containing hydrocarbons, carbon monoxide, nitrogen oxides, and sulfur oxides initially encounter the upper washcoat layer 16 and then the lower washcoat layer 14.

Preparation of catalyst composite

The catalyst composite can be readily prepared by methods well known in the art. Representative processes are set forth below. As used herein, the term "washcoat" is used in the general sense in the art to be a thin adherent coating of catalytic or other material applied to a substrate support material, such as a honeycomb-type support member, which is sufficiently porous to allow the treated gas stream to pass therethrough.

Catalyst composites in the form of layers can be readily prepared on monolithic supports. For the first layer of a particular washcoat layer, finely divided particles of a high surface area refractory metal oxide are slurried in a suitable vehicle (e.g., water). The support may then be impregnated one or more times in such a slurry, or the slurry may be coated on the support to deposit a desired loading of metal oxide on the support, e.g., about 0.5 to about 2.5g/in per impregnation³. To incorporate components such as precious metals (e.g., palladium, rhodium, platinum, and/or combinations thereof), stabilizers, and/or promoters, such components can be incorporated into the slurry in the form of a mixture of water-soluble or water-dispersible compounds or complexes. Thereafter, the coated support is calcined by heating, for example, at 400 ℃ to 600 ℃ for about 10 minutes to about 3 hours. For the purposes of the present invention, the term "platinum component" means any compound, complex, or the like, typically a metal or metal oxide, that decomposes or otherwise converts to a catalytically active form upon calcination or use thereof. Typically, when palladium is desired, the palladium component is used in the form of a compound or complex to effect dispersion of the component on a refractory metal oxide support (e.g., silica-alumina). For the purposes of the present invention, the term "palladium component" means any compound, complex, or the like, typically a metal or metal oxide, that decomposes or otherwise converts to a catalytically active form upon calcination or use thereof. Water-soluble compounds or water-dispersible compounds or complexes of the metal component may be used so long as the liquid medium used to impregnate the refractory metal oxide support particles or deposit the metal component onto the refractory metal oxide support particles does not adversely react with the metal or its compound or its complex or other components that may be present in the catalyst composition and is capable of being removed from the metal component by volatilization or decomposition upon heating and/or application of a vacuum. In some cases, complete removal of the liquid may not be possibleUntil the catalyst is placed into service and subjected to the high temperatures encountered during operation. Generally, from an economic and environmental point of view, aqueous solutions of soluble compounds or complexes of noble metals are utilized. Suitable compounds are, for example, chloroplatinic acid of palladium nitrate or tetraaminopalladium nitrate or platinum, amine-solubilized platinum hydroxide, etc. Such compounds are converted into the catalytically active form of the metal or compound thereof during the calcination step, or at least in the initial stage of use of the composite.

A suitable method of preparing any layer of the layered catalyst composite of the present invention is to prepare a mixture of a solution of the desired noble metal compound (e.g., palladium compound) and at least one support, such as a finely divided high surface area refractory metal oxide support, e.g., silica-alumina, which is sufficiently dry to absorb substantially all of the solution to form a wet solid, which is later combined with water to form a coatable slurry. In one or more embodiments, the slurry is acidic, having a pH of, for example, about 2 to less than about 7. The pH of the slurry may be lowered by adding a sufficient amount of an inorganic or organic acid to the slurry. When the compatibility of the acid with the raw material is considered, a combination of both may be used. Inorganic acids include, but are not limited to, nitric acid. Organic acids include, but are not limited to, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutamic acid, adipic acid, maleic acid, fumaric acid, phthalic acid, tartaric acid, citric acid, and the like. Thereafter, if desired, a water-soluble or water-dispersible compound or stabilizer (e.g., barium acetate) and a promoter (e.g., lanthanum nitrate) may be added to the slurry.

In one embodiment, the slurry is thereafter comminuted such that substantially all solids have a particle size of less than about 20 microns, i.e., an average diameter of between about 0.1 and 15 microns. Comminution may be achieved in a ball mill or other similar device, and the solids content of the slurry may be, for example, about 20-60 wt%, more specifically about 30-40 wt%.

The other layers, i.e. the second layer and the third layer, may be prepared and deposited on the first layer in the same way as described above for the deposition of the first layer on the carrier.

Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. In the following, preferred designs for layered catalysts are provided, including combinations such as used alone or in unlimited combinations, the uses of which include the systems and methods of other aspects of the invention.

As previously discussed, the catalyst composition of the present invention includes two layers employing two distinct compositions of platinum group metals. The first washcoat layer or upper washcoat layer comprises zeolite, Pt and a refractory metal oxide support. In some embodiments, the upper washcoat layer is substantially free of palladium. The second washcoat layer or lower washcoat layer contains platinum and palladium in a Pt to Pd weight ratio between 9:1 and 1: 4. In one embodiment, the total noble metal component loading is from 5 to 500g/ft, in grams of noble metal per volume of the bulk³Preferably 10 to 250g/ft³Preferably 15 to 150g/ft³。

In one embodiment, the high Pt layer for NO oxidation and the lower Pt: Pd layer for CO/HC oxidation are reversed. The platinum and palladium are present in the upper washcoat layer in a Pt to Pd weight ratio in the range of about 1:4 to 10:1, more specifically in the range of 1:1 to 5:1, and even more specifically in the range of about 1:1 to 2:1, and in this embodiment, the lower washcoat layer has a high Pt to Pd weight ratio of about 5:1 to 100:1, more specifically 5:1 to 10: 1. The total loading of Pt and Pd in the lower washcoat layer was about 90g/ft³And the total loading of Pt and Pd in the washover layer is about 30g/ft³. The noble metal loading of this embodiment can be used to improve CO reduction while still maintaining improved NO oxidation.

In one or more embodiments, the total loading of platinum (Pt) in the upper washcoat layer is at about 10g/ft³To 120g/ft³Within the range. In some embodiments, the total Pt in the upper washcoat layer is at about 60g/ft³To 120g/ft³In the range or even about 10 to 60g/ft³. In thatIn some embodiments, the total loading of platinum and palladium in the top washcoat layer is at about 70g/ft³To 120g/ft³In the range or alternatively at about 10g/ft³To 60g/ft³Within the range. In one or more embodiments, the total loading of platinum in the lower washcoat layer is at about 5g/ft³To 85g/ft³In the range and a total loading of palladium in the lower washcoat layer of about 5g/ft³To 50g/ft³Within the range. In one or more embodiments of the invention, the total combined platinum and palladium content in the upper washcoat layer and the lower washcoat layer is present in a Pt to Pd weight ratio of about 4: 1. In some embodiments, the composite contains a platinum group metal in the upper layer relative to the weight ratio in the lower layer in a range of about 1:4 to 4: 1. In one or more embodiments, the composite material contains a platinum group metal in the upper layer relative to the weight ratio in the lower layer in a range of about 2:1 to 4:1, or alternatively in a range of about 1:3 to 1: 1. In one or more embodiments, the lower washcoat layer comprises a Pt to Pd weight ratio of Pt and Pd in a range from about 1:4 to 4: 1. In other embodiments, the upper washcoat layer comprises Pt to Pd components in a Pt to Pd weight ratio in a range of about 1:1 to 100: 1.

In various embodiments, the compositions of the upper and lower washcoat layers described above may be reversed. For example, in one or more embodiments, the upper washcoat layer comprises a Pt component and a Pd component in a Pt to Pd weight ratio in a range of about 9:1 to 1: 4. In other embodiments, the lower washcoat layer comprises a Pt to Pd weight ratio of Pt and Pd in a range from about 1:1 to 100: 1. In one or more embodiments, the lower cladding layer comprises barium oxide in the range of about 3 to about 30g/ft³Within the range.

In some aspects of the invention, the composite material may be suitable for oxidizing NO to NO₂. In particular, the composite material may be suitable for NO₂Formed in total NO_xIn the range of about 40% to 60%.

Exhaust system for lean burn engine

Another aspect of the invention relates to an emission treatment system for treating diesel exhaust emissions, comprising one or more ofA seed component and a catalyst composite as described herein. An exemplary emission treatment system may be more readily understood by reference to fig. 3, which depicts a schematic representation of an emission treatment system 32 according to this embodiment of the invention. Referring to FIG. 3, gaseous pollutants (e.g., unburned hydrocarbons, carbon monoxide, and NO) will be contained via exhaust gas delivery line 36_x) And particulate matter, is delivered from a lean burn engine 34, such as a diesel engine, to a Diesel Oxidation Catalyst (DOC)38 in the form of a catalyst composite according to an embodiment of the invention. In the DOC 38, unburned gaseous volatile hydrocarbons (i.e., VOF) and carbon monoxide are largely combusted to form carbon dioxide and water. In addition, NO_xA proportion of the NO in the component may be oxidised to NO in the DOC₂. The exhaust stream is then delivered via an exhaust line 40 to a Catalyzed Soot Filter (CSF)42 that traps particulate matter present in the exhaust stream. CSF 42 optionally catalyzes passive regeneration. After removal of the particulate matter via the CSF 42, the exhaust gas flow is conveyed via an exhaust line 44. An ammonia precursor (e.g., an aqueous urea solution) is injected into exhaust line 44 via line 23. The ammonia-added exhaust stream is delivered via line 44 to a downstream Selective Catalytic Reduction (SCR) assembly 46 for NO sequestration_xFor treatment and/or transformation.

Another exemplary emission treatment system is shown in FIG. 4, which depicts a schematic representation of an emission treatment system 48 according to an embodiment of the present invention. Referring to FIG. 4, the exhaust line 36 will contain gaseous pollutants (e.g., unburned hydrocarbons, carbon monoxide, and NO)_x) And particulate matter, is delivered from a lean burn engine 34, such as a diesel engine, to a Diesel Oxidation Catalyst (DOC)38 in the form of a catalyst composite according to an embodiment of the invention. In the DOC 38, unburned gaseous volatile hydrocarbons (i.e., VOF) and carbon monoxide are largely combusted to form carbon dioxide and water. In addition, NO_xA proportion of the NO in the component may be oxidised to NO in the DOC₂. The exhaust gas flow is then conveyed via an exhaust line 44. An ammonia precursor (e.g., an aqueous urea solution) is injected into exhaust line 44 via line 23. Selective catalysis of the ammonia-added exhaust stream via line 44 to a catalytic soot Filter (SCRoF)50For trapping particulate matter present in the exhaust stream and for NO_xFor treatment and/or transformation. Optionally, the exhaust stream may be delivered via line 52 to a downstream Selective Catalytic Reducer (SCR)53 for NO_xFor further processing and/or transformation.

Another exemplary emission treatment system can be seen in FIG. 5, which depicts a schematic representation of an emission treatment system 54 according to an embodiment of the present invention. Referring to FIG. 5, the exhaust line 36 will contain gaseous pollutants (e.g., unburned hydrocarbons, carbon monoxide, and NO)_x) And particulate matter, is delivered from a lean burn engine 34, such as a diesel engine, to a Diesel Oxidation Catalyst (DOC)38 in the form of a catalyst composite according to an embodiment of the invention. In the DOC 38, unburned gaseous non-volatile hydrocarbons (i.e., VOF) and carbon monoxide are largely combusted to form carbon dioxide and water. In addition, NO_xA proportion of the NO in the component may be oxidised to NO in the DOC₂. The exhaust stream is then conveyed via line 44. An ammonia precursor (e.g., an aqueous urea solution) is injected into exhaust line 44 via line 23. The ammonia-added exhaust stream is delivered via line 44 to a downstream Selective Catalytic Reduction (SCR) assembly 56 for NO sequestration_xFor treatment and/or transformation. Optionally, the exhaust stream may be conveyed via line 58 to a Catalyzed Soot Filter (CSF)60 to trap particulate matter present in the exhaust stream.

The SCR catalyst (46, 50, 53, or 56) may be effective to reduce NO by selective catalytic reduction with ammonia at a temperature in a range of about 150 ℃ to about 600 ℃_xAny composition in which the components are converted to nitrogen. Suitable catalysts include vanadium oxide supported on a W-doped titania or base metal (such as copper and/or iron) promoted zeolite. Suitable zeolites include ZSM-5, beta, USY, CHA, and the like. Particular embodiments relate to zeolites having 8-ring pore openings and double six-ring secondary building units, for example, those having the following structure types: AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV. In accordance with one or more embodiments, it should be appreciated that by defining the structure type of the zeolite, it is intended to include such things as SAPO, ALPO, and MeAPO having the same structure typeMaterials, etc. structural types and any and all homogeneous types of frame materials. In a more specific embodiment, reference to an aluminosilicate zeolite structure type limits the material to zeolites that do not include phosphorus or other metals substituted in the framework. Of course, the aluminosilicate zeolite may then be ion-exchanged with one or more promoter metals, such as iron, copper, manganese, cobalt, nickel, cerium or platinum group metals. However, for the sake of clarity, as used herein, "aluminosilicate zeolites" do not include aluminophosphate materials such as SAPO, ALPO, and MeAPO materials, and the broader term "zeolites" is intended to include aluminosilicates and silica-alumina-phosphate oxides (SAPOs).

In a specific system embodiment, when a base metal promoted small pore zeolite having 8-membered ring openings (about 3.8 angstroms) accessible through its 3-dimensional pores is used as the zeolite for the SCR catalyst, it is possible to integrate the SCR catalyst with the CSF. More specifically, CSF in the form of a wall flow filter is loaded with a washcoat of copper and/or iron promoted small pore zeolites having 8-membered ring openings. In a specific embodiment, the zeolite has the CHA crystal structure. The copper and/or iron promoted zeolite loading on the wall flow filter can be at 0.5g/ft³To 2.4g/ft³Within the range. In a specific embodiment, 0.5g/ft is illustrated³、0.6g/ft³、0.7g/ft³、0.8g/ft³、0.9g/ft³、1.0g/ft³、1.1g/ft³、1.2g/ft³、1.3g/ft³、1.4g/ft³、1.5g/ft³、2.4g/ft³The amount of the supported catalyst. In some embodiments, it may be possible to remove the downstream SCR catalyst 53 from the system, thereby reducing the footprint of the overall system configuration because fewer components are used. In particular embodiments, the washcoat is in the form of a slurry-supported washcoat obtained from the application of a suspension of zeolite solid particles in a liquid vehicle (such as water) applied to a wall-flow filter such that the washcoat may be on the surface of the filter and/or permeate the filter walls.

The diesel oxidation catalyst composite according to the present invention may be readily applied to various emission treatment systems. According to the invention, DOC composites with improved NO oxidation can be used in DOC + CSF or DOC + CSF + SCR systems for passive soot combustion, in DOC + SCR or DOC + SCR + CSF systems for improving SCR performance with Fe and or Cu zeolite SCR catalysts, or in DOC + SCR on catalyzed soot filters (DOC + scref) systems for improving scref performance.

Examples

The following non-limiting examples will serve to illustrate various embodiments of the present invention. In various embodiments, the carrier is cordierite. The reference to the upper and lower washcoat layers does not limit the location of the coating on the support.

Example 1

An oxidation catalyst composite having the following two layers was prepared: a lower washcoat layer and an upper washcoat layer. The layered catalyst composite contains palladium and platinum with a total noble metal loading of about 120g/ft³And a nominal Pt/Pd/Rh weight ratio of about 4/1/0. The substrate has 5.3in³A volume of (0.09L), a cell density of 400 cells per square inch, and a wall thickness of about 100 μm. Each layer was prepared as follows:

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 1.7% by dry weight), Pt (about 1% by dry weight), and Pd (about 1% by dry weight), wherein the nominal Pt/Pd weight ratio is 1/1. The total loading of the washdown layer was 1.6g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry (45-50% solids slurry) was formed by combining silica-alumina with water and acidified to a pH <4.5 and ground to 90% particle size less than 8 microns. The slurry is coated onto the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus lower washcoat layer was dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Top wash coat

The components present in the upper washcoat layer were high surface area silica-alumina, H beta zeolite (about 42% by dry weight), a suitable binder (about 4% by dry weight), and Pt (about 6% by dry weight), with a nominal Pt/Pd weight ratio of 1: 0. The total loading of the outer layer was 1.2g/in³。

Platinum in the form of an amine salt was impregnated onto silica-alumina by a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry of silica-alumina is formed and the pH is lowered to <4.5 using an acid. The slurry was milled to 90% particle size less than 16 microns. Zeolite is added to the slurry. The slurry was then milled to 90% particle size less than 10 microns. A binder is added to the slurry. The slurry is coated onto the lower washcoat layer on the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus the lower washcoat layer and the upper washcoat layer were dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Example 2

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 1.7% by dry weight), Pt (about 2.2% by dry weight), and Pd (about 0.9% by dry weight), wherein the nominal Pt to Pd weight ratio is 2.5: 1. The total loading of the washdown layer was 1.6g/in³。

Top wash coat

The components present in the upper washcoat layer were high surface area silica-alumina, H beta zeolite, a suitable binder (about 4% by dry weight), and Pt (about 3.5% by dry weight), with a nominal Pt to Pd weight ratio of 1: 0. The total loading of the top wash coat was 1.2g/in³。

Platinum in the form of an amine salt was impregnated onto silica-alumina by a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry of silica-alumina is formed and the pH is lowered to <4.5 using an acid. The slurry was milled to 90% particle size less than 16 microns. The zeolite is then added to the slurry. The slurry was then milled to 90% particle size less than 10 microns. A binder is added to the slurry. The slurry is coated onto the lower washcoat layer on the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus the lower washcoat layer and the upper washcoat layer were dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Example 3

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 1.7% by dry weight), Pt (about 0.2% by dry weight), and Pd (about 0.9% by dry weight), wherein the nominal Pt/Pd weight ratio is 1/4. Lower wash coatThe total loading of (A) is 1.6g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry of silica-alumina is formed, pH is lowered to <4.5 using an acid, and milled to 90% particle size less than 8 microns. The slurry is coated onto the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus lower washcoat layer was dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Top wash coat

The components present in the upper washcoat layer were high surface area silica-alumina, H beta zeolite, a suitable binder (about 4% by dry weight), and a Pt mixture (about 8% by dry weight), where the nominal Pt to Pd weight ratio was 1: 0. The total loading of the top wash coat was 1.2g/in³。

Example 4

An oxidation catalyst composite having the following two layers was prepared: a lower washcoat layer and an upper washcoat layer. The layered catalyst composite contains palladium and platinum with a total noble metal loading of about 120g/ft³And a nominal Pt/Pd/Rh weight ratio of about 4/1/0. The substrate has 5.3in³A volume of (0.09L), a cell density of 400 cells per square inch, and a wall thickness of about 100 μm. Each layer was prepared as follows：

Lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 0.6% by dry weight), Pt (about 2.8% by dry weight), and Pd (about 0.3% by dry weight), wherein the nominal Pt to Pd weight ratio is about 9: 1. The total loading of the washdown layer was 1.6g/in³。

Top wash coat

The components present in the upper washcoat layer were high surface area silica-alumina, H beta zeolite, a suitable binder (about 4% by dry weight), barium hydroxide (about 1.4% by dry weight), Pd (about 0.7% by dry weight), and Pt (about 0.7% by dry weight), with a nominal Pt to Pd weight ratio of about 1: 1. The total loading of the top wash coat was about 1.2g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. The slurry was milled to 90% particle size less than 16 microns. The zeolite is then added to the slurry. The slurry was then milled to 90% particle size less than 10 microns. A binder is added to the slurry. The slurry is coated onto the lower washcoat layer on the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus the lower washcoat layer and the upper washcoat layer were dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Comparative example 5

Preparation of a composition havingComparative oxidation catalyst composite of the following two layers: an upper washcoat layer and a lower washcoat layer. The layered catalyst composite contains palladium and platinum with a total noble metal loading of about 120g/ft³And a nominal Pt/Pd/Rh weight ratio of 4/1/0. The substrate has 5.3in³A volume of (0.09L), a cell density of 400 cells per square inch, and a wall thickness of about 100 μm. Each layer was prepared as follows:

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 1% by dry weight) and the noble metals platinum (about 2.3% by dry weight) and palladium (about 0.6% by dry weight), wherein the nominal Pt/Pd weight ratio is 4/1. The total loading of the washdown layer was about 1.2g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry is then formed, using an acid to lower the pH. The slurry was milled to 90% particle size less than about 10 microns. The slurry is coated onto the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus lower washcoat layer is dried and then calcined.

Top wash coat

The component present in the top-wash coating is a high surface area (180 m)²(iv)/g) silica-alumina, H beta zeolite, binder (about 3% by dry weight), barium hydroxide (about 0.9% by dry weight), and noble metals platinum (about 2.8% by dry weight) and palladium (about 0.7% by dry weight), wherein the nominal Pt/Pd weight ratio is 4/1. The total loading of the top wash coat was 1.6g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry is then formed, using an acid to lower the pH. The slurry was milled to 90% particle size less than 16 microns. The zeolite is then added to the slurry. The slurry was then milled to 90% particle size less than 10 microns. A binder is added to the slurry. The slurry is coated onto the lower washcoat layer on the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus the lower washcoat layer and the upper washcoat layer were dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Example 6

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina and Pt (about 3.3% by dry weight), wherein the nominal Pt/Pd weight ratio is 1/0. The total loading of the washdown layer was 1.6g/in³。

Platinum in the form of an amine salt was impregnated onto silica-alumina by a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry of silica-alumina is formed, pH is lowered to <4.5 using an acid, and milled to 90% particle size less than 8 microns. The slurry is coated onto the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus lower washcoat layer was dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Top wash coat

The components present in the upper washcoat layer were high surface area silica-alumina, H beta zeolite, a suitable binder (about 4% by dry weight), barium hydroxide (about 2.3% by dry weight), Pt (about 0.6% by dry weight), and Pd (about 2.3% by dry weight), with a nominal Pt to Pd weight ratio of 1: 4. The total loading of the top wash coat was 1.2g/in³。

Palladium in the form of a palladium nitrate solution and platinum in the form of an amine salt were impregnated onto silica-alumina by means of a planetary mixer (P-mixer) to form a wet powder while achieving incipient wetness. An aqueous slurry of silica-alumina is formed and the pH is lowered to <4.5 using an acid. The slurry was milled to 90% particle size less than 16 microns. The zeolite is then added to the slurry. The slurry was then milled to 90% particle size less than 10 microns. A binder is added to the slurry. The slurry is coated onto the lower washcoat layer on the cordierite substrate using deposition methods known in the art for depositing catalysts on cordierite substrates. After coating, the support plus the lower washcoat layer and the upper washcoat layer were dried and then calcined at a temperature of 450 ℃ for about 1 hour.

Example 7

lower wash coat

The component present in the lower cladding is a high surface area (180 m)²(iv)/g) silica-alumina, barium hydroxide (about 1.0% by dry weight), Pt (about 0.5% by dry weight), and Pd (about 0.5% by dry weight), wherein the nominal Pt to Pd weight ratio is 1: 1. The total loading of the washdown layer was 1.6g/in³。

Top wash coat

Upper washing coverThe components present in the layer are high surface area silica-alumina, H beta zeolite, a suitable binder (about 4% by dry weight), barium hydroxide (about 0.8% by dry weight), Pt (about 7.8% by dry weight), and Pd (about 0.9% by dry weight), with a nominal Pt to Pd weight ratio of 9: 1. The total loading of the top wash coat was 1.2g/in³。

Example 8 testing

The composites of examples 1 to 5 were tested as follows. Catalyst composites of size 1 "x 3" were aged in a laboratory oven with 10% steam at approximately 800 ℃ for 16 hours. After aging, the layered catalysts of examples 1-5 were tested in a transient laboratory reactor using EURO 5 test cycles. Measured average NO₂Formation and CO conversion are reported in table 1.

Table 1: NO₂/NO_xAnd CO performance

The test results in table 1 demonstrate the benefit of using a catalyst having an overlayer that is substantially free of Pd and comprises Pt and zeolite.For each of the catalyst composites described in examples 1-7, NO₂There was a significant improvement in forming the aging reference relative to example 5. It is noteworthy that aged examples 1 to 4 and examples 6 to 7 all have NO at least as effective as fresh reference example 5₂And (4) forming. In addition, the CO conversion efficiency was not substantially changed in aged examples 1 to 7 when compared with aged reference example 5.

Example 9 testing

The composites of example 1, example 2 and example 5 were further tested as follows. Catalyst composites of size 1.5 "x 4" were aged in a laboratory oven with 10% steam at approximately 800 ℃ for 16 hours. After aging, the layered catalysts of example 1, example 2 and example 5 were tested in a transient laboratory reactor using a DOC and a scref system. The SCREF used in conjunction with the DOC is loaded at 1.5g/in³A wall flow filter of CuCHA zeolite. There is no separate SCR catalyst downstream of SCR on a wall flow filter (scruf). Mean removal of NO_xThe performance is reported in table 2.

Table 2: NO removal for DOC + SCRoF_xPerformance%

The results of these tests in table 2 demonstrate the benefit of using a catalyst having an overlayer that is substantially free of Pd and comprises Pt and zeolite. NO removal for DOC + SCRoF System for each of the catalyst composites described in examples 1 and 2_xThe performance is significantly improved relative to the aging reference of example 5. It is noted that both aged example 1 and example 2 have substantially equal NO removal as fresh reference example 5_xAnd (4) performance.

Examples 1-2 also demonstrate the feasibility of systems consisting of DOC catalyst composites according to embodiments of the invention with downstream SCR catalysts supported on wall flow filters (scrofs) and without other downstream SCR catalysts or filters catalyzed by platinum group metals. It is therefore possible to integrate the system and reduce the size.

Example 10 testing

The composites of examples 1 to 7 were further tested as follows. The fully sized catalyst composite (5.66 "Dx 4" L) was oven aged at about 800 ℃ under 10% steam for 16 hours. The layered catalysts of examples 1 to 5 were tested on a 2.0L diesel engine after aging. Average NO for specifying European NEDC driving cycle₂Formation, CO conversion and HC conversion performance are reported in table 3.

Table 3: NO₂Formation, CO conversion and HC conversion

The results of these vehicle conversion tests in table 3 again demonstrate the benefit of using a catalyst having an overlayer that is substantially free of Pd and comprises Pt and zeolite. For each of the catalyst composites described in examples 1-4 and 6-7, NO₂There was a significant improvement in forming the aging reference relative to example 5. In addition, each aged catalyst composite in examples 1-7 had an equal or only modest reduction in CO conversion when compared to the aged reference of comparative example 5. Further, the HC conversion rates of aged examples 1 to 7 were approximately equal to the aged reference of example 5.

It should be emphasized that the above-described embodiments of the present invention, particularly any "preferred" embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Reference in the specification to "one embodiment," "certain embodiments," "one or more embodiments," or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

The present invention has been specifically described with reference to the embodiments described above and modifications thereof. Modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention.

Claims

1. An oxidation catalyst composite for reducing exhaust gas emissions from a lean burn engine, comprising:

a support substrate having a length, an inlet end and an outlet end, an oxidation catalyst catalytic material on the support, the oxidation catalyst catalytic material comprising a lower washcoat layer and an upper washcoat layer;

the lower washcoat layer comprising a refractory metal oxide support, a platinum (Pt) component, and a palladium (Pd) component, the Pt to Pd weight ratio being in a range of about 1:1 to 1: 4; and is

The washcoat layer comprising zeolite, Pt, and a refractory metal oxide support, the washcoat layer being substantially free of palladium, the oxidation catalyst composite being effective to reduce hydrocarbons and carbon monoxide and oxidize NO in the lean burn engine exhaust to NO₂(ii) a And is

Wherein the upper washcoat layer contains a higher loading of platinum group metal than the lower washcoat layer to maximize NO oxidation.

2. The oxidation catalyst of claim 1, wherein the upper washcoat layer is substantially free of barium and the lower washcoat layer is substantially free of zeolite.

3. The oxidation catalyst of claim 1 or 2, wherein the lower washcoat layer comprises a Pt component in an amount of about 5g/ft³To 85g/ft³In the range and including a Pd component in an amount of about 5g/ft³To 50g/ft³Within the range.

4. An oxidation catalyst as set forth in any one of claims 1-3 wherein the composite material comprises a platinum group metal in the upper layer relative to the lower layer in a weight ratio in the range of from 1:1 to 4: 1.

5. The oxidation catalyst of any one of claims 1-4, wherein the upper washcoat layer comprises platinum at about 60 to 120g/ft³Within the range.

6. The oxidation catalyst of any one of claims 1-5, wherein the upper washcoat layer comprises platinum at about 10 to 60g/ft³Within the range.

7. An oxidation catalyst composite for reducing exhaust gas emissions from a lean burn engine, comprising:

the upper washcoat layer comprising a refractory metal oxide, a zeolite, and a platinum component (Pt) and a palladium component (Pd), the Pt to Pd weight ratio being in the range of about 9:1 to 1: 4; and is

The undercushion layer comprises Pt and a refractory metal oxide support, and the oxidation catalyst composite is effective to reduce hydrocarbons and carbon monoxide and oxidize NO in the lean burn engine exhaust to NO₂。

8. The oxidation catalyst of claim 7, wherein the lower washcoat layer is substantially free of palladium and substantially free of barium.

9. The oxidation catalyst as set forth in claim 7 or 8 wherein the lower washcoat layer further comprises a palladium component, the platinum component being present in a Pt to Pd weight ratio with the palladium component in a range of about 1:1 to 100: 1.

10. The oxidation catalyst of claim 7 or 8 wherein the lower washcoat layer further comprises a washcoat concentration in the range of about 3-30g/ft³Barium oxide within the range.

11. A method of treating exhaust gas from a lean burn engine, the method comprising flowing the exhaust gas through a honeycomb substrate coated with an oxidation catalyst composite of any one of claims 1-10, wherein the diesel oxidation catalyst is effective to reduce CO and HC and oxidize NO from the exhaust stream to NO₂。

12. A system for treating lean burn engine exhaust emissions comprising hydrocarbons, carbon monoxide, and other exhaust gas components, the emissions treatment system comprising:

an exhaust conduit in fluid communication with the lean burn engine via an exhaust manifold;

the oxidation catalyst composite of any one of claims 1-10, wherein the support substrate is a flow-through substrate or a wall-flow substrate; and is

A catalyzed soot filter and an SCR catalyst composition are located downstream of the oxidation catalyst composite.

13. The system of claim 12, wherein the SCR catalyst composition comprises a vanadium oxide supported on W-doped titania or an iron or copper promoted small pore zeolite with 8-membered ring openings.