JPH0724740B2 - Exhaust gas purifying catalyst and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a catalyst for purifying diesel engine exhaust gas or industrial exhaust gas containing combustible carbon fine particles and a method for producing the same.

In recent years, particulate matter in diesel engine exhaust gas (mainly composed of solid carbon particulates, sulfur particulates such as sulfates, and liquid or solid high molecular weight hydrocarbon particulates) tends to become a problem for environmental hygiene. This is because these fine particles have a particle diameter of almost 1 micron or less, are easily suspended in the air, and are easily taken into the human body by respiration. Therefore, studies are underway in the direction of tightening regulations on the emission of these fine particles from diesel engines.

By the way, methods for removing these fine particles are roughly classified into the following two methods. One is to use a heat resistant gas filter (ceramic foam, wire mesh, metal foam, plugged type ceramic honeycomb, etc.) to pass the exhaust gas, trap fine particles, and accumulate them with a burner if the pressure loss rises. The method of burning fine particles to regenerate the filter, and the other method is to reduce the frequency of the above combustion regeneration by supporting the catalyst substance on the carrier with this heat resistant gas filter structure and performing the combustion operation together with the overoperation. This is a method of increasing the combustion activity of the catalyst to the extent that there is no need.

In the former case, the higher the removal effect of fine particles, the faster the pressure loss rises, the more frequently the regeneration occurs, the more troublesome, and the economically disadvantageous. In contrast, the latter method is considered to be a much better method if a catalytic substance capable of effectively maintaining the catalytic activity under the emission conditions (gas composition and temperature) of diesel engine exhaust gas is adopted.

However, the exhaust gas temperature of a diesel engine is much lower than that of a gasoline engine, and since a light oil is used as a fuel, a sulfur compound, especially its oxide, mainly sulfur dioxide (SO ₂ ) is also contained in the exhaust gas. Many are included. Therefore, it has almost no ability to generate sulfates (SO ₂ is further oxidized to SO ₃ or sulfuric acid mist), and it has the ability to satisfactorily ignite and burn fine particles accumulated within the temperature obtained under normal engine running conditions. In spite of the demand for the above-mentioned exhaust gas purifying catalyst having the above-mentioned characteristics, a catalyst which sufficiently meets this condition has not been proposed so far.

[Conventional technology]

Various proposals have hitherto been made for the purpose of enhancing the effect of capturing carbonaceous fine particles. An attempt was made to adhere a heat-resistant inorganic fiber to the inner wall of the through hole of the structure having the through hole to enhance the capturing effect of the carbonaceous fine particles (JP-A-59-142820), or the inner wall of the ceramic honeycomb structure having the through hole. Attempt to capture carbonaceous fine particles by providing a large number of irregularly arranged protrusions on the surface (Japanese Patent Laid-Open No. 57-99314)
Japanese Patent Laid-Open Publication No. 1993-242242), and proposes a carrier that enhances the trapping effect of carbonaceous fine particles by forming coarse particles on an open honeycomb or a plug honeycomb or by foaming the wall surface to form protrusions, followed by drying and firing. (JP-A-58-14921).

However, to improve the contact efficiency with the carbonaceous fine particles that accumulate by accumulating catalytically active components in the form of protrusions on the gas inlet side of the partition having the gas filter function as disclosed in the present invention,
At present, there is no disclosure of one having improved catalytic combustion performance.

[Problems to be solved by the invention]

The present inventors propose a catalyst that can burn carbonaceous fine particles contained in exhaust gas from a diesel engine from a lower temperature, and a method for preparing the same.

The catalyst according to the present invention is highly evaluated in the following points. The exhaust gas temperature from the diesel engine is much lower than that of a gasoline vehicle, and the exhaust gas temperature during city driving does not reach 450 ° C even at the manifold outlet, so a catalyst with good combustion of carbon fine particles is required even at 350 ° C or less. .

However, the conventionally proposed catalyst is trapped because the catalyst component is supported in a layer by fine particles on the wall surface of the gas contact portion of the three-dimensional structure or on the inner wall surface of the inner pores of the partition aggregate. The contact efficiency with the carbonaceous particles is poor,
At present, it is not possible to derive sufficient combustion performance from catalytically active substances.

The inventors of the present invention have noticed that the carbonaceous fine particles accumulate in layers on the side wall surface of the gas inlet of the partition having a filter function. The inventors have found that the catalytic performance is remarkably improved by increasing the contact efficiency between the carbonaceous fine particles and the carbon fine particles, and have completed the present invention.

[Means for solving problems]

 The present invention is specified as follows.

(1) A catalyst comprising a refractory three-dimensional structure having a gas filter function, and an adhesion film made of coarse particulate projections containing a catalytically active component formed on a gas inlet side wall surface of the refractory three-dimensional structure,
80% or more of particles in which the coarse-grained projections exceed 40 μm, and
An exhaust gas-purifying catalyst, characterized in that it is formed of coarse particles having a particle size of 300 μm or less.

(2) A refractory three-dimensional structure having a gas filter function is composed of a large number of gas distribution pipes, the distribution pipes are alternately open at their inlets and closed at their outlets, and an inlet. A ceramic monolith (plug honeycomb), which is composed of a flow tube that is closed and is open at the outlet, and the wall of the flow tube that is adjacent to the flow tube is a porous partition wall having a gas filter function. Above (1)
The described catalyst.

(3) When forming an adhered film made of coarse granular protrusions containing a catalytically active component on the side wall surface of the gas inlet of the refractory three-dimensional structure having a gas filter function, the coarse granular protrusions exceed 12 μm. Of 80% or more and 300 μm or less are formed as coarse particles, and the coarse particles are at least 1 selected from the group consisting of alumina sol, titania sol, zirconia sol, silica sol, soluble boehmite, and soluble organic polymer compound. A method for producing an exhaust gas-purifying catalyst, characterized in that an aqueous slurry is used together with one kind of dispersant, and this is injected from the gas inlet side of the refractory three-dimensional structure.

In the partition walls having a filter function of a commercially available plug honeycomb carrier, an infinite number of pores having an average diameter of about 12 μm to 40 μm exist. When carrying a catalytically active component on the carrier, it is preferable to catalyze without raising the ventilation back pressure inherent to the carrier so much. In the present invention, a protrusion is formed on the gas inlet side wall surface without blocking the pores. It was found that the catalytic efficiency can be remarkably improved by increasing the contact efficiency with the carbonaceous fine particles accumulated here by adhering the catalytically active component to form a catalyst.

In the conventional washcoat technology, the active ingredient is loaded in a layer on the wall surface of the gas inlet side carrier or is also loaded in the pores to increase the back pressure of the three-dimensional structure, and as a result, the catalytic function can be sufficiently extracted. There were no drawbacks.

Therefore, the first feature of the present invention is that coarse particles containing a catalyst component having an appropriate particle size that does not close the pores of the partition walls having a filter function are used.

Here, examples of the material forming the three-dimensional structure having a gas filter function include cordierite, mullite, lithium aluminum silicate, spinel, alumina, zirconia, silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ) and the like. . Of these, cordierite is preferred,
Mullite and lithium aluminum silicate are used.

Further, in the present invention, as the catalytically active component, vanadium, manganese, copper, molybdenum, chromium, cobalt, nickel, iron, zinc, silver, tungsten, niobium, potassium, sodium, cesium, alkali metal such as rubidium, barium, calcium. , Strontium, magnesium, and other alkaline earth metals, platinum, rhodium, palladium, lanthanum, and at least one metal compound selected from the group consisting of cerium, and these active ingredients are mixed or supported to form coarse particles. Examples of the heat-resistant inorganic substance used for forming the adhered film include activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, and zeolite. Suitable A.

The coarse-grained adhered film-forming product according to the present invention (hereinafter, also referred to as “coarse-grained substance”) has a particle size not exceeding 300 μm, as described above, and has an average pore size (normally Is at least 80%, preferably 90% or more. In that case, coarse particles composed of only catalytically active components (particularly preferably sparingly water-soluble) may be used, or the above-mentioned heat-resistant inorganic substance powder may be loaded with a catalytically active component and used as coarse particles. It may be prepared, with particular success if used in the latter form.

The method for preparing the catalyst according to the present invention is not specified, but the following method is preferred as an example.

That is, activated alumina pellets are impregnated and supported with an aqueous solution of a water-soluble salt of a catalytically active component, dried and calcined. Next is a hammer mill (for example, PULVERIZER manufactured by Hosokawa Micron Co., Ltd.)
Crushed with a classifier (eg Hosokawa Micron,
MICRON SEPARATOR, MS-O type), and fine particles are removed so that 80% or more of the particles have a particle size larger than the average pore size of the partition walls having a filter function.
Coarse particles of 300 μm or more are removed with a sieve.

The classified particles are then treated with soluble boehmite (eg
CONDEA's DISPERAL) converted to alumina (Al ₂ O ₃ ) 1
Add to an aqueous solution containing ~ 20 wt% and stir. Due to the thickening effect of boehmite as a dispersant, a stable slurry can be obtained without sedimenting the granular active substance not only during stirring but also when stirring is stopped. The slurry is charged from the gas inlet portion in an amount 10 to 50% higher than the water absorption amount of the plug honeycomb carrier, and the excess slurry is blown by air blowing to match the desired supported amount. Then dry, 200-800 ℃, especially 300
Bake at a temperature of ~ 700 ° C.

In this preparation method, when slurrying the coarse particulate catalytically active component, alumina having a thickening effect so that coarse particles do not settle, titania, zirconia, sol such as silica and soluble boehmite, a group consisting of soluble organic polymer compounds The soluble organic polymer compound may be used in the form of an aqueous slurry together with at least one dispersant selected from the group consisting of sodium polyacrylate, ammonium polyacrylate and sodium acrylic acid-maleic acid copolymer. Salts or ammonium salts, polyethylene oxide, polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, starch, gum arabic, guar gum, glue and the like are preferably used. Further, for the purpose of improving the carrying strength of the coarse-particle catalytically active component, an inorganic fibrous substance such as glass fiber, alumina fiber, silicon nitride (Si
₃ N ₄ ), silicon carbide (SiC), potassium titanate, rock wool, etc. may be dispersed.

In order to make the catalyst coat layer more porous, a method of adding a soluble organic polymer compound such as polyethylene glycol to the slurry and removing it by firing may be used in combination. When 20% or more of fine particles smaller than the average pore size of the partition walls are present in the slurry, it is not preferable because the back pressure is increased when used as a catalyst. Also, 300 μm
Larger coarse particles are not preferable because they settle quickly in the slurry and it is difficult to uniformly support them on the carrier, and even if they are supported, their adhesive strength is not sufficient.

In addition, as a preparation method suitable for the present invention, a coarse product of a heat-resistant inorganic substance (having the same classified particle size as above) is preliminarily supported on a three-dimensional structure, and the water-soluble or organic compound of the catalytically active component is added. A solution of a solvent-soluble salt may be impregnated and supported for catalysis.

The preparation method is not limited to this, and any method may be used as long as the catalyst active component is supported in the form of protrusions on the gas inlet side wall surface of the partition having a gas filter function.

In the catalyst according to the present invention, the amount of the catalytically active component supported is not particularly limited, but it is 10 to 200 g, preferably 20 per 100 g of the catalyst as coarse particles defined by the present invention.
It is in the range of ~ 150g. And, as the heat-resistant inorganic substance, a range of 5 to 150 g, preferably 10 to 120 g, per catalyst,
The catalytically active component is an oxide or metal per catalyst
It is in the range of 0.01 to 50 g, preferably 0.05 to 30 g.

[Action]

The combustion reaction of carbonaceous fine particles is a solid-solid reaction, and the contact efficiency between the catalytically active substance and the carbonaceous fine particles is a very important factor.

In view of this point, the present invention has the action and effect of the present invention in that the catalyst particulate matter is supported on the side wall surface of the gas inlet in a protrusion shape and the contact efficiency is positively improved to significantly improve the activity.

Hereinafter, the present invention will be specifically described by showing Examples and Comparative Examples of the present invention.

Example 1 Commercially available activated alumina pellets (3-5 mmφ, surface area 150 m ²
/ g) Weigh 1 kg, and ammonium metavanadate 290 g
Aqueous solution 1 was prepared by adding 435 g of oxalic acid to and dissolving it, and after impregnating it, it was pulled up and dried at 150 ° C for 3 hours, and then in air at 500 ° C.
It was baked for 2 hours. The pellets were crushed with a hammer mill and classified with a classifier such that 30 μm or less was 20% or less. Coarse particles of 300 μm or more were removed using a sieve. The particle size of the resulting coarse-grained active material is less than 30 μm 12.5%, 30-45 μm 13.5%, 45-74 μm 22%, 74
~ 105μm 27%, 105-149μm 12%, 149-300μm
It had a particle size distribution of 13% and had an average particle size of 75 μm.

150 g of the classified powder catalyst was dispersed in an aqueous solution prepared by previously dissolving 15 g of soluble boehmite (11.25 g in terms of Al ₂ O ₃ ) to obtain 520 ml of stable slurry.

The viscosity of this slurry was 25 cps (room temperature).

As the carrier, a commercially available plug honeycomb (material: cordierite) having a diameter of 5.66 inches × 6.0 inches, 100 cells / square inch, and a wall thickness of 17 mil was used. The average pore diameter of the partition walls of the carrier was 30 μm.

520 ml of the above slurry was poured from the side of the gas inlet of the carrier, and the excess slurry was removed by blowing air from the opposite side. Then, it was dried at 150 ° C. for 3 hours and calcined in air at 500 ° C. for 2 hours to obtain a finished catalyst.

The loading amount of each component of the finished product is Al ₂ O ₃ 40 g / − carrier, V ₂ O ₅
9 g / -carrier. It was observed that this catalyst formed a laminated film of coarse particles on the wall surface of the carrier without blocking the pores.

Example 2 Commercially available titania pellets (3-5 mmφ, surface area 30 m ² / g) 1
An aqueous solution of 276 g of ammonium molybdate dissolved in kg
Impregnate 450 ml and dry at 150 ° C for 3 hours, 500 ° C in air
It was baked for 2 hours.

The pellets were pulverized and classified in the same manner as in Example 1 (average particle size 65 μm). Using 150 g of the classified powder catalyst, it was catalyzed in the same manner as in Example 1. The viscosity of the slurry used was 28 cps.

The loading amount of each component of the finished product is TiO ₂ 40 g / − carrier, MoO ₃
9 g / -carrier.

Example 3 As in Example 1, platinum (P
t) and rhodium (Rh) were supported to obtain a classified powder catalyst. Pt was a nitric acid solution of dinitrodiammine platinum, and Ph was a rhodium nitrate solution. The powder catalyst was loaded on the same three-dimensional structure as that used in Example 1 to prepare a catalyst.

The amount of each finished component loaded is Al ₂ O ₃ 40 g /-carrier, Pt
It was 0.9 g / -carrier and Rh 0.1 g / -carrier.

Example 4 Titania-silica pellets (Ti
O ₂ / SiO ₂ molar ratio = 4/1) copper nitrate in the same manner as in Example 1 to _{[Cu (NO 3) 2 · 6H} 2 O ] copper oxide using [CuO]
Was carried and the classified powder catalyst was obtained.

A catalyst was prepared by supporting the powder catalyst on the same three-dimensional structure as that used in Example 1.

The loading amount of each component was TiO ₂ —SiO ₂ 40 g / − carrier and CuO 9 g / − carrier.

Example 5 In the same manner as in Example 1, pellets of the heat-resistant inorganic substance were loaded with the catalytically active substances shown in Table 1 to obtain a classified powder catalyst. The powder catalyst was loaded on the same three-dimensional structure as used in Example 1 to load the catalyst substances shown in Table 1.

Example 6 150 g of a powder catalyst of MoO ₃ -supporting titania prepared by pulverizing and classifying in the same manner as in Example 2 was used to previously prepare ammonium polyacrylate (Aquaric NL manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) as a solid content. As a result, 1% by weight was dispersed in the dissolved aqueous solution to obtain 520 ml of stable slurry. As in Example 1, the slurry was used to catalyze.

The loading amount of each component of the finished product is TiO ₂ 40 g / − carrier, MoO ₃
9 g / -carrier.

Comparative Example 1 V ₂ O ₅ -supporting alumina pellets prepared in the same manner as in Example 1 were pulverized with a hammer mill and then wet pulverized with an ordinary wet mill to obtain a slurry having an average particle diameter of 0.8 μm.

Using the slurry, the same three-dimensional structure as used in Example 1 was dipped and supported, excess slurry was removed by air blow, dried at 150 ° C. for 3 hours, and calcined at 500 ° C. for 2 hours to obtain a catalyst. Turned into

The loading amount of the finished catalyst component is Al ₂ O ₃ 40 g / -support, V ₂
Although it was O ₅ 9 g / − carrier, it was confirmed that the amount of clogging in the pores was larger than that of the carrier on the wall surface of the carrier and the carrier was in a non-uniform state.

Comparative Example 2 ZrO ₂ pellets having the same composition as obtained in Example 5-4 were pulverized and wet pulverized with a wet mill in the same manner as in Comparative Example 1 to obtain a slurry having an average particle size of 1.0 μm. . When a catalyst was prepared in the same manner as in Example 1 using the slurry, the amount of the finished catalyst component supported was MnO ₂ 5
g / - carrier, CuO 4g / - carrier, ZrO ₂ 40g / - was carrier.

Example 7 Regarding the catalysts obtained in Examples 1-6 and Comparative Examples 1-2,
A catalyst evaluation test was performed using a 2300 cc 4-cylinder diesel engine. Fine particles were captured for about 2 hours under the conditions of an engine speed of 2500 rpm and a torque of 4.0 kg · m, and then the torque was increased at intervals of 0.5 kg · m every 5 minutes to continuously record the pressure loss change of the catalyst layer. The temperature at which the pressure rise due to the accumulation of fine particles and the pressure drop due to the combustion of fine particles become equal (Te) and the pressure loss rapidly decreases (Ti) as the exhaust gas temperature rises on the catalyst
I asked. Further, the change over time in pressure loss when trapping fine particles at 2500 rpm and a torque of 4.0 kg · m was calculated from the pressure loss change amount per hour from the chart to obtain the value of ΔP (mmHg / Hr).

The results are shown in Table 2.

Continuation of the front page (56) Reference JP 59-142820 (JP, A) JP 57-99314 (JP, A) JP 58-14921 (JP, A) JP 59-49825 (JP , A) JP-A-57-147415 (JP, A)

Claims (3)

[Claims] 1. A catalyst comprising a fire-resistant three-dimensional structure having a gas filter function, wherein an adhering film composed of coarse-grained projections containing a catalytically active component is formed on a side wall surface of a gas inlet of the fire-resistant three-dimensional structure. An exhaust gas-purifying catalyst, characterized in that the projections are formed of coarse particles having a particle size of 40 μm or more and 80% or more and 300 μm or less. 2. A refractory three-dimensional structure having a gas filter function is composed of a large number of gas flow pipes, and the flow pipes have alternately open inlets and closed outlets. A ceramic monolith (plug honeycomb), which is composed of a flow pipe having an inlet closed and an outlet open, and the wall of the flow pipe adjacent to the flow pipe is a porous partition wall having a gas filter function. The catalyst according to claim (1). 3. When forming an adhered film made of coarse granular projections containing a catalytically active component on the side wall surface of a gas inlet of a refractory three-dimensional structure having a gas filter function, the coarse granular projections have a thickness of 12 μm. Over 80% of particles and 300
formed of coarse particles having a particle size of not more than μm, and the coarse particles together with at least one dispersant selected from the group consisting of alumina sol, titania sol, zirconia sol, silica sol, soluble boehmite, and soluble organic polymer compound. A method for producing a catalyst for exhaust gas purification, which comprises using an aqueous slurry and injecting it from the gas inlet side of a refractory three-dimensional structure.