JPH1085604A - Catalyst for cleaning of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning of exhaust gas having improved durability as compared with the conventional catalyst and having superior purifying performance even in the early stage and even after use at a high temp. SOLUTION: This catalyst is a monolithic catalyst with catalytic component carrying layers and contains silicon nitride (Si3 N4 ) and/or boron nitride(BN), silicon carbide(SiC), rhodium and platinum and/or palladium as catalytic components. Silicon nitride and/or boron nitride is especially contained in a platinum-and/or palladium-contg. layer especially disposed on the inner layer side and silicon carbide is especially contained in a rhodium-contg. layer especially disposed on the surface layer side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and, more particularly, to hydrocarbons (hereinafter referred to as "HC") and carbon monoxide (hereinafter referred to as "HC") in exhaust gas discharged from an internal combustion engine of an automobile or the like. "CO") and nitrogen oxides (hereinafter, referred to as "CO").
The present invention relates to an exhaust gas purifying catalyst that can efficiently purify NOx) and has excellent purifying performance even after high-temperature durability.

[0002]

2. Description of the Related Art Conventionally, exhaust gas purifying catalysts have inadequate durability, and the purifying performance of the catalyst is remarkably reduced after high-temperature durability. Therefore, even after high-temperature durability, the catalyst has excellent low-temperature activity and steady conversion performance. The development of exhaust gas purifying catalysts is expected.

Conventionally, at least one of platinum, rhodium, and palladium has been used as an active species of an exhaust gas purifying catalyst for automobiles, and activated alumina having a high specific surface area has been widely used as a carrier of the active species. I have been. However, the conventionally used activated alumina has insufficient thermal stability, and the crystal structure changes at high temperature, and B
A phase transition occurs to α-alumina having an extremely small ED specific surface area. When the crystal structure of alumina changes in this way,
There is a problem that the sintering and aggregation of the noble metal are promoted, and a solid phase reaction occurs between the alumina and the noble metal to form an inactive compound.
Accordingly, in recent years, a device has been devised to improve the durability of the catalyst by incorporating a ceramic material having high heat resistance into the catalyst without forming an inert compound due to the reaction between the alumina and the noble metal. I have been.

As a catalyst containing a ceramic material, for example, JP-A-59-52529,
Japanese Patent Application Laid-Open Nos. 233146 and 7-23209 and the like.

Japanese Patent Application Laid-Open No. 59-52529 discloses that γ-
Addition of metal and ceramic whiskers to alumina improves the adhesion between the catalyst carrier and the catalyst coat layer, suppresses the occurrence of cracks in the catalyst, and improves exhaust gas purification catalyst with improved heat resistance compared to conventional catalysts Is disclosed.

Japanese Patent Application Laid-Open No. 233146/1990 discloses that by using silicon nitride (Si ₃ N ₄ ) or silicon carbide (SiC) together with an organometallic compound of silicon as a binder, rearrangement of zeolite particles and There is disclosed an exhaust gas purifying catalyst which suppresses densification and has improved heat resistance as compared with the related art.

[0007] Japanese Patent Publication No. 7-23209 discloses that rhodium (Rh) or platinum (Pt) is added to SiC produced by a special production method and having a high specific surface area of 100 m ² / g or more.
A catalyst for purifying exhaust gas which has high activity even at high temperature by carrying is disclosed.

[0008]

However, the above-mentioned Japanese Patent Application Laid-Open No.
The catalysts described in JP-A-9-52529 and JP-A-2-233146 aim to suppress generation of cracks and densification of zeolite particles by adding ceramics such as Si ₃ N ₄ or SiC to the catalyst. On the other hand, the precious metal itself, which is a catalytically active species, has not been stabilized or its durability has not been improved, so it can be said that the heat resistance has been improved compared to the past, but it is still not possible to obtain sufficient heat resistance and purification performance. was there.

[0009] The catalyst described in Japanese Patent Publication No. 7-23209 attempts to improve thermal stability by using a high specific surface area type SiC as a noble metal-carrying substrate, but the initial performance is insufficient. There was a problem that it was expensive.

In recent catalysts, a SiC carrier is used as a carrier having excellent heat resistance in place of a conventional cordierite honeycomb carrier, or a catalyst layer formed by utilizing a difference in thermal conductivity between alumina and SiC. Although heat removal is promoted, a sufficient improvement effect on heat resistance and catalytic performance has not been obtained.

Accordingly, an object of the present invention is to provide an exhaust gas purifying catalyst which has improved durability over conventional catalysts and has excellent purification performance even at an initial stage and after high-temperature durability.

[0012]

The present inventors have conducted research to solve the above-mentioned problems, and as a result, as a catalyst component, silicon nitride (Si ₃ N ₄ ) and / or boron nitride (BN)
The present inventors have found that a catalyst having excellent purification performance can be obtained even at an initial stage and after high-temperature durability by containing silicon carbide (SiC), rhodium, platinum and palladium, and have reached the present invention.

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising an integrated catalyst having a catalyst component-supporting layer, wherein silicon nitride (Si ₃ N ₄ ) and / or
Or boron nitride (BN), silicon carbide (SiC),
It is characterized by containing rhodium and platinum and / or palladium.

Further, in order to effectively exhibit the catalyst performance after durability of the exhaust gas purifying catalyst according to the first aspect,
Considering the compatibility between the base material and the noble metal, the exhaust gas purifying catalyst according to claim 2, wherein the platinum and / or palladium-containing layer contains silicon nitride and / or boron nitride, and the rhodium-containing layer contains the carbon nitride. It is characterized by containing silicon.

Further, in order to efficiently exhibit the synergistic effect of the exhaust gas purifying performance between the noble metals in the exhaust gas purifying catalyst according to the second aspect, the exhaust gas purifying catalyst according to the third aspect comprises platinum and / or platinum. The palladium-containing layer is disposed on the inner layer side, and the rhodium-containing layer is disposed on the surface layer side.

Further, in order to improve the initial performance of the exhaust gas purifying catalyst according to any one of claims 1 to 3, the exhaust gas purifying catalyst according to claim 4 further contains alumina powder. It is characterized by.

Further, in order to prevent peeling of the catalyst coat layer of the exhaust gas purifying catalyst according to the fourth aspect, the exhaust gas purifying catalyst according to the fifth aspect is characterized in that silicon nitride and / or boron nitride and silicon carbide are used. The content ratio of alumina powder is
It is characterized in that the powder weight ratio is 3/7 to 8/2.

Further, in order to improve the thermal stability of alumina of the catalyst for purifying exhaust gas according to claim 4 or 5, the catalyst for purifying exhaust gas according to claim 6 is characterized in that cerium, zirconium and lanthanum are added to the alumina powder. Wherein at least one member selected from the group consisting of 1 to 10 mol% in terms of metal is contained.

Further, in order to further improve the catalytic activity of the exhaust gas purifying catalyst according to any one of claims 1 to 6 in a reducing (rich) atmosphere, the exhaust gas purifying catalyst according to claim 7 is 1 to 40 mol% of a metal selected from the group consisting of cerium, neodymium and lanthanum
And zirconium oxide whose balance is zirconium.

Furthermore, in order to improve the low-temperature activity of the exhaust gas purifying catalyst according to any one of claims 1 to 7, and the catalytic activity and durability under a stoichiometric air-fuel ratio (stoichiometric) atmosphere, the catalyst according to claim 8 is improved. The exhaust gas purifying catalyst further comprises 1 to 40 mol% of a metal selected from the group consisting of zirconium, neodymium and lanthanum in terms of metal, and the remainder contains cerium oxide which is cerium. I do.

Further, in order to improve the low-temperature activity and the catalytic activity in a rich atmosphere of the exhaust gas purifying catalyst according to any one of claims 1 to 8, the exhaust gas purifying catalyst according to claim 9 further comprises: , At least one selected from the group consisting of alkali metals and alkaline earth metals.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The exhaust gas purifying catalyst of the present invention will be described below. As the ceramic component contained in the exhaust gas purifying catalyst of the present invention, the catalytic component of the noble metal, which is an active species, is sufficiently exhibited, and further, the base material and the noble metal after high-temperature durability are inhibited from growing grains. In order to maintain the dispersibility, silicon nitride (Si ₃ N ₄ ) and / or boron nitride (BN) having excellent heat resistance and silicon carbide (SiC) are suitable. SiC, Si ₃ N ₄ and BN have α-type,
There are many types of crystal structures such as β-type, hexagonal, tetragonal, etc.
It can be used in the present invention irrespective of these crystal structures.

The noble metals contained in the catalyst component supporting layer of the exhaust gas purifying catalyst of the present invention include rhodium, platinum and / or palladium. The content of these noble metals is preferably 0.1 to 15 g in 1 L of the catalyst. If the content is less than 0.1 g, the low-temperature activity and purification performance are not sufficiently exhibited.
If it exceeds 5 g, the catalytic activity of the noble metal is saturated, and it is not economically effective.

Further, in order to effectively exhibit the activity of the noble metal, it is important to select a base material suitable for the noble metal type, and the platinum and / or palladium-containing layer is more preferably made of nitride powder than silicon carbide. (Silicon nitride and / or boron nitride), and the rhodium-containing layer preferably contains silicon carbide rather than the nitride powder. It is particularly preferable that the platinum and / or palladium-containing layer is disposed on the inner layer side and the rhodium-containing layer is disposed on the surface layer side.

Further, the exhaust gas purifying catalyst preferably further contains alumina powder. As the alumina powder, activated alumina powder is particularly preferably used.
Activated alumina has a larger specific surface area than silicon nitride (Si ₃ N ₄ ) and / or boron nitride (BN) and silicon carbide, so that noble metal dispersibility is better and more sufficient catalytic performance can be obtained. . Accordingly, by dispersing the noble metal and gas diffusion in the initial state by increasing the alumina powder having a large specific surface area, particularly activated alumina, in the catalyst component layer, the low-temperature activity and the catalytic performance are improved.

It is preferable that the content ratio of the alumina powder to silicon nitride and / or boron nitride and silicon carbide is 3/7 to 8/2 in terms of powder weight ratio. If it is smaller than 3/7, the amount of silicon nitride and / or boron nitride and silicon carbide is small, so that the effect of improving the high-temperature durability performance cannot be sufficiently obtained. On the other hand, if it is larger than 8/2, the initial performance cannot be sufficiently obtained,
Further, since the catalyst slurry of silicon nitride and / or boron nitride and silicon carbide lacks adhesion to the catalyst carrier, the catalyst coat layer is easily peeled off.

In particular, the alumina is selected from the group consisting of cerium, zirconium and lanthanum in order to enhance the structural stability of the alumina after high-temperature durability and to suppress the phase transition to α-alumina and the decrease in the BET specific surface area. It is preferable that at least one of these is contained in an amount of 1 to 10 mol% in terms of metal. If the amount is less than 1 mol%, a sufficient effect cannot be obtained.
If it exceeds 10 mol%, the effect of addition will be saturated. The amount of the alumina used is 10 to 200 g per liter of the catalyst.
It is. If the amount is less than 10 g, sufficient dispersibility of the noble metal cannot be obtained, and even if the amount is more than 200 g, the catalytic performance is saturated, and a remarkable improvement effect cannot be obtained.

Further, it is preferable that the zirconium oxide contains a zirconium oxide containing one selected from the group consisting of cerium, neodymium and lanthanum.
One element selected from the group consisting of cerium, neodymium and lanthanum is contained in an amount of 1 to 40 mol% in terms of metal, and the remainder is zirconium. The reason for setting the content to 1 to 40 mol% is that at least one element selected from the group consisting of cerium, neodymium and lanthanum is added to zirconium oxide (ZrO ₂ ), and the oxygen releasing ability of ZrO ₂ and BET
This is because the specific surface area and further the thermal stability are remarkably improved. If it is less than 1 mol%, it is the same as the case of ZrO ₂ alone,
The effect of adding the above-mentioned elements does not appear, and if it exceeds 40 mol%, this effect is saturated or reduced.

When the zirconium oxide powder is contained in the catalyst component-supporting layer, the zirconium oxide having a high oxygen storage capacity releases lattice oxygen and adsorbed oxygen in a rich atmosphere and near stoichiometric conditions, thereby reducing the oxidation state of the noble metal. In order to make the catalyst suitable for purifying exhaust gas, it is possible to suppress a decrease in catalytic performance of the noble metal.

Further, it is preferable that the cerium oxide contains a cerium oxide containing one selected from the group consisting of zirconium, neodymium and lanthanum, and the cerium oxide is one selected from the group consisting of zirconium, neodymium and lanthanum. It contains 1 to 40 mol% in terms of metal, and the balance is cerium. By containing such a cerium oxide, the cerium oxide having a high oxygen storage capacity releases lattice oxygen and adsorbed oxygen in a rich atmosphere and in the vicinity of stoichiometry, thereby making the oxidation state of the noble metal suitable for purifying exhaust gas, and Performance degradation can be suppressed. The reason for setting the content to 1 to 40 mol% is that cerium oxide (CeO ₂ ) contains zirconium,
By adding at least one element selected from the group consisting of neodymium and lanthanum, the oxygen releasing ability of CeO ₂ and B
This is because the ET specific surface area and the thermal stability are remarkably improved.
If it is less than 1 mol%, the effect of adding the above-mentioned elements does not appear as in the case of only CeO ₂ , and if it exceeds 40 mol%, this effect is saturated or conversely decreases.

Further, those containing an alkali metal and / or an alkaline earth metal are preferable, and the alkali metal and / or the alkaline earth metal used include lithium, sodium, potassium, cesium, magnesium, and the like.
Includes calcium, strontium and barium.
When these are contained in the catalyst component-supporting layer, the action of poisoning by HC adsorption under a rich atmosphere is reduced, and the sintering of noble metals is suppressed, so that the activity at a low temperature or under a reducing atmosphere can be further improved. it can. Its content is catalyst 1
It is 1 to 40 g in L. If the amount is less than 1 g, adsorption poisoning of hydrocarbons and sintering of a noble metal cannot be suppressed, and even if the amount exceeds 40 g, a significant effect of increasing the amount cannot be obtained, and conversely, the performance is reduced.

In producing the exhaust gas purifying catalyst of the present invention, various noble metals are mixed with Si ₃ N ₄ and / or BN,
The method of supporting SiC and alumina can be appropriately selected from known methods such as an impregnation method and a kneading method.

As the raw material compound of the noble metal, any compound can be used as long as it is a water-soluble one such as dinitrodiamminate, chloride and nitrate. The removal of water can be appropriately selected from known methods such as a filtration method and an evaporation to dryness method.

Noble metal-supported alumina, noble metal-supported Si ₃ N ₄ and / or BN, and noble metal-supported S used in the present invention
The first heat treatment for obtaining the iC is not particularly limited, but in order to support the added noble metal with good dispersibility, baking is performed at a relatively low temperature of, for example, 400 ° C to 800 ° C in the air and / or under the flow of air. Is preferred, whereby a catalyst powder is obtained.

Further, Si ₃ N ₄ and / or BN and / or SiC and / or alumina powder can be added simply to the catalyst powder without carrying a noble metal.

Preferably, a zirconium oxide powder containing at least one selected from the group consisting of cerium, neodymium and lanthanum can be added to the catalyst powder. By adding a zirconium oxide powder containing at least one selected from the group consisting of cerium, neodymium and lanthanum, under a reducing atmosphere, the oxidation state of the noble metal is more effectively maintained in a state suitable for exhaust gas purification. can do.

More preferably, by adding a cerium oxide containing at least one selected from the group consisting of zirconium, neodymium and lanthanum, the oxidation state of the noble metal is reduced in a reducing atmosphere to a state suitable for exhaust gas purification. In addition, it can be maintained more effectively.

The exhaust gas purifying catalyst according to the present invention thus obtained can be effectively used without a carrier. However, it is pulverized and slurry, coated on the catalyst carrier and calcined at 400 to 900 ° C. It is preferable to use them.

Specifically, the above Si ₃ N ₄ and / or BN
And platinum and / or palladium, or even SiC and rhodium, to the alumina powder, and if necessary, the zirconium oxide powder and / or the cerium oxide powder, and further add alumina sol to the wet Pulverized into a slurry, adhered to the catalyst carrier, and
The calcination is carried out in air and / or under a flow of air at a temperature in the range of 50 ° C.

The catalyst carrier can be appropriately selected from known catalyst carriers and used, for example, a monolith carrier or a metal carrier made of a refractory material. Although the shape of the catalyst carrier is not particularly limited, it is generally preferable to use the catalyst carrier in a honeycomb shape. The catalyst powder is applied to various honeycomb base materials.

As the honeycomb material, cordierite materials such as ceramics are generally used.
It is also possible to use a honeycomb material made of a metal material such as ferrite stainless steel, and further, the catalyst component powder itself may be formed into a honeycomb shape. By making the shape of the catalyst into a honeycomb shape, the contact area between the catalyst and the exhaust gas is increased and the pressure loss can be suppressed, so that it is extremely effective when used as an exhaust gas purifying catalyst for automobiles.

The amount of the catalyst component coat layer adhered to the honeycomb material is preferably 50 g to 400 g per liter of the catalyst in total of the entire catalyst components. The larger the number of catalyst component supporting layers, the more preferable in terms of catalyst activity and catalyst life.However, if the coating layer is too thick, the reaction gas will be insufficiently diffused inside the catalyst component supporting layer and cannot be sufficiently contacted with the catalyst. The effect of increasing the volume is saturated, and the gas passage resistance is increased. Therefore, the amount of the coat layer is preferably 50 g to 400 g per liter of the catalyst.

Further, in order to efficiently exhibit the synergistic effect of the exhaust gas purification performance between the noble metals, the catalyst component layer containing platinum and / or palladium is located below the coat layer (the inner layer side).
, And the rhodium-containing catalyst component layer is disposed on the upper side (surface layer side) of the coat layer. Platinum may be contained in the same catalyst component layer as rhodium, and may be arranged above the coating layer (surface layer side).

More preferably, the obtained exhaust gas purifying catalyst may be impregnated with an alkali metal and / or an alkaline earth metal. Alkali metals and alkaline earth metals that can be used include lithium, sodium,
It is at least one element selected from the group consisting of potassium, cesium, magnesium, calcium, strontium, and barium.

The alkali metal and alkaline earth metal compounds which can be used are water-soluble compounds such as oxides, acetates and hydroxides. This makes it possible to carry a basic element, an alkali metal and / or an alkaline earth metal, with good dispersibility in the vicinity of the noble metal.

That is, an aqueous solution of a powder comprising an alkali metal and / or alkaline earth metal compound is impregnated into the above-mentioned carrier carrying a washcoat component, dried, and then dried in air and / or under a stream of air for 200 to 600 hours. It is fired at a relatively low temperature of ° C. The firing temperature is 200 ° C
If it is less than the above, the alkali metal and alkaline earth metal compounds cannot be sufficiently converted into the oxide form. Conversely, even if the temperature exceeds 600 ° C., the effect of the sintering temperature is saturated, and no remarkable difference is obtained.

[0047]

The present invention will be described with reference to the following examples and comparative examples.

Example 1 Alumina powder containing 3 mol% of Ce was impregnated with an aqueous solution of dinitrodiammine platinum or sprayed while stirring at a high speed.
After drying at 0 ° C. for 24 hours, it was calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain a Pt-supported Ce-containing alumina powder (powder A). The Pt concentration of this powder A was 1.1% by weight.

The Si ₃ N ₄ powder is impregnated with an aqueous solution of dinitrodiammine platinum or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, and then 600 ° C.
Baked at ℃ for 1 hour, Pt-supported Si ₃ N ₄ powder (powder B)
I got The Pt concentration of this powder B was 1.1% by weight.

An alumina powder containing 3 mol% of Zr is impregnated with an aqueous rhodium nitrate solution or sprayed while stirring at a high speed.
After drying at 50 ° C. for 24 hours, the mixture was calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Rh-supported Zr-containing alumina powder (powder C). The Rh concentration of this powder C was 1.7.
% By weight.

The SiC powder was impregnated with an aqueous rhodium nitrate solution or sprayed while stirring at a high speed, dried at 150 ° C. for 24 hours, calcined at 400 ° C. for 1 hour, and then at 600 ° C. for 1 hour to obtain a Rh-supported SiC powder (powder). D) was obtained. This powder D
Was 1.0% by weight.

74 g of powder A, 74 g of powder B, Z
r 30 mol% supported cerium oxide powder 124 g and nitric acid acidic alumina sol 229 g (sol obtained by adding 10% by weight of nitric acid to 10% by weight of boehmite alumina) were put into a magnetic ball mill, mixed and pulverized,
A slurry liquid was obtained in which the content ratio between the i ₃ N ₄ powder and the alumina powder was 1/1 by weight. This slurry liquid was adhered to a cordierite-based monolith carrier, excess slurry in the cell was removed with an air stream, dried, and calcined at 400 ° C. for 1 hour. This operation was performed twice to obtain catalyst-A having a coat layer weight of 200 g / L and a carrier.

The above powder D67g, the above powder C38g, C
e, 111 g of zirconium oxide powder containing 30 mol%,
29 g of alumina powder containing 3 mol% of Zr and 256 g of nitric acid acidic alumina sol are put into a magnetic ball mill, mixed and pulverized, and the content ratio of SiC powder and alumina powder is
A slurry liquid having a weight ratio of 5.4 / 4.6 was obtained. This slurry liquid was adhered to the above-mentioned coated catalyst-A, and the excess slurry in the cell was removed by an air stream and dried.
It was baked at 0 ° C. for 1 hour to apply a coat layer weight of 45 g / L to obtain an exhaust gas purifying catalyst. The cerium oxide powder and the alumina powder may further contain lanthanum, neodymium, and the like.

Example 2 Pt was prepared in the same manner as in the preparation of powder B using BN powder.
A supported BN powder (powder E) was prepared, and an exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that powder E was used instead of powder B in the production of the catalyst.

Example 3 Pt was added in an amount of 2.18% by weight in the same manner as when powder A was prepared.
A supported Pt-supported Ce-containing alumina powder (powder F) was prepared, and this powder F 74 g, Si ₃ N ₄ powder 74 g, Zr
124 g of 30 mol% supported cerium oxide powder and 229 g of nitric acid acidic alumina sol (a sol obtained by adding 10% by weight of nitric acid to 10% by weight of boehmite alumina) were charged into a magnetic ball mill, mixed and pulverized to obtain Si.
₃ content ratio of N ₄ powder and the alumina powder to obtain a slurry liquid comprising 5.4 / 4.6 by weight ratio. This slurry liquid was adhered to a cordierite-based monolithic carrier, excess slurry in the cells was removed by an air stream, and the slurry was dried.
It was baked at 0 ° C. for 1 hour. This operation was performed twice to obtain catalyst B having a coat layer weight of 200 g / L and a carrier.

In the same manner as that for preparing powder C, Rh-supported Zr-containing alumina powder (powder G) supporting 1.96% by weight of Rh was prepared, and 67 g of this powder G and 6 g of SiC powder were prepared.
7 g, 111 g of zirconium oxide powder containing 30 mol% of Ce and 256 g of nitric acid acidic alumina sol were put into a magnetic ball mill, mixed and pulverized, and the content ratio of SiC powder and alumina-based powder was reduced to 1/1 by weight. A slurry liquid was obtained. This slurry liquid was adhered to the above-mentioned coat catalyst-B, excess slurry in the cell was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coat layer weight of 45.
g / L to obtain an exhaust gas purifying catalyst. The cerium oxide powder and the alumina powder may further contain lanthanum, neodymium, and the like.

Example 4 An exhaust gas purifying catalyst was obtained in the same manner as in Example 3 except that BN powder was used instead of Si ₃ N ₄ powder.

Example 5 An alumina powder containing 3 mol% of Ce was impregnated with an aqueous solution of dinitrodiammine palladium or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, and then at 600 ° C. By calcining for 1 hour, a Pd-supported Ce-containing alumina powder (powder H) was obtained. The Pd concentration of this powder H was 1.7% by weight. Powder H further contains lanthanum,
Zirconium, neodymium, etc. may be included.

The Si ₃ N ₄ powder is impregnated with an aqueous solution of dinitrodiammine palladium or sprayed while stirring at a high speed.
After drying at 0 ° C. for 24 hours, it was baked at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Pd-supported Si ₃ N ₄ powder (powder I). The Pd concentration of this powder I was 1.7% by weight.

An aqueous solution of dinitrodiammine palladium is impregnated or sprayed with high-speed stirring on cerium oxide powder supporting 30 mol% of Zr, and dried at 150 ° C. for 24 hours.
Firing at 400 ° C. for 1 hour, then at 600 ° C. for 1 hour, P
A d-supported Zr-containing cerium oxide powder (powder J) was obtained.
The Pd concentration of this powder J was 0.75% by weight.

73 g of powder H, 73 g of powder I, 100 g of powder J and 254 g of nitric acid acidic alumina sol
(A sol obtained by adding 10% by weight of nitric acid to 10% by weight of boehmite alumina) was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is adhered to a cordierite-based monolithic carrier, excess slurry in the cell is removed by an air stream, and the slurry is dried.
It was baked at 00 ° C. for 1 hour. This operation was performed twice to obtain catalyst-C having a coat layer weight of 200 g / L and a carrier.

Powder D67g obtained in Example 1, Powder C
38 g, 111 g of zirconium oxide powder containing 30 mol% of Ce, 29 g of alumina powder containing 3 mol% of Zr, and 256 g of nitric acid acidic alumina sol were put into a magnetic ball mill, mixed and pulverized, and the content ratio of SiC powder and alumina powder was reduced. A slurry liquid having a weight ratio of 5.1 / 4.9 was obtained. This slurry liquid was adhered to the above-mentioned coat catalyst-C, excess slurry in the cell was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to obtain a coat layer weight of 45 g /
L was applied to obtain Catalyst-D. The cerium oxide powder and the alumina powder may further contain lanthanum, neodymium, and the like.

Next, after a barium acetate solution was applied to the above-mentioned catalyst-D, it was baked at 400 ° C. for 1 hour to contain 20 g / L as BaO. Further, after a potassium acetate solution was adhered in the same procedure, it was calcined at 400 ° C. for 1 hour to obtain an exhaust gas purifying catalyst containing 1 g / L as K ₂ O.

Example 6 BN powder was impregnated with an aqueous solution of dinitrodiammine palladium or sprayed while stirring at a high speed, dried at 150 ° C. for 24 hours, calcined at 400 ° C. for 1 hour, and then at 600 ° C. for 1 hour to obtain Pd-supported BN powder (powder K) was obtained. This powder K
Had a Pd concentration of 1.7% by weight. An exhaust gas purifying catalyst was obtained in the same manner as in Example 5, except that the powder K was used instead of the powder I.

Example 7 Pd-supported Ce-containing alumina powder (powder L) carrying 3.4% by weight of Pd was prepared in the same manner as powder H was prepared, and 73 g of this powder L, 73 g of Si ₃ N ₄ powder, Of a zirconium oxide powder containing 30 mol% and 254 g of a nitric acid acidic alumina sol are charged into a magnetic ball mill, mixed and pulverized, and the content ratio of the Si ₃ N ₄ powder to the alumina powder is 5.5 / 4. 5 was obtained. A catalyst component-carrying cordierite monolithic carrier was obtained in the same manner as in Example 3 except that a catalyst having a coat layer weight of 200 g / L-carrier was obtained instead of the catalyst-B using this slurry liquid. After attaching a barium acetate solution to the cordierite monolithic carrier carrying the catalyst component, it was calcined at 400 ° C. for 1 hour to obtain 20 g / BaO as BaO.
L was added to obtain an exhaust gas purifying catalyst.

Example 8 An exhaust gas purifying catalyst was obtained in the same manner as in Example 7, except that BN powder was used instead of Si ₃ N ₄ powder.

Comparative Example 1 Alumina powder A was used instead of powder B, and powder C was used instead of powder D.
₃ N _4, except that it was decided not to use the SiC is Example 1
An exhaust gas purifying catalyst was obtained in the same manner as described above.

Comparative Example 2 The content ratio of Si ₃ N ₄ powder to alumina powder and Si
The content ratio of C powder and alumina powder is 2 /
Except that slurry liquid No. 8 was obtained, an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

Comparative Example 3 The content ratio of Si ₃ N ₄ powder to alumina powder and Si
The content ratio between the C powder and the alumina powder is 9 /
Except for obtaining the slurry liquid to be 1, an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

Comparative Example 4 Powder H was used in place of Powder I, and Powder C was used in place of Powder D. Si ₃ N ₄ , SiC
Except that no was used, an exhaust gas purifying catalyst was obtained in the same manner as in Example 5.

Table 1 shows the compositions in the exhaust gas purifying catalysts obtained in Examples 1 to 8 and Comparative Examples 1 to 4.

[0072]

[Table 1]

Test Examples The exhaust gas purifying catalysts of Examples 1 to 8 and Comparative Examples 1 to 4 were mounted on a 4500 cc engine manufactured by Nissan Motor Co., Ltd., and were subjected to durability under the following durability conditions. The activity was evaluated.

Endurance conditions Engine displacement 4500cc Fuel unleaded gasoline Catalyst inlet gas temperature 850 ° C Endurance time 30 hours Inlet gas composition CO 0.5 ± 0.1% O ₂ 0.5 ± 0.1% HC Approx.1100ppm NO 1300ppm CO ₂ 15%

The purifying performance of each exhaust gas purifying catalyst in the initial stage and after the endurance is expressed by the average conversion (%) of each HC, CO and NOx in the stoichiometric atmosphere, which is determined by the following equations (1) to (3). Table 2 shows the results.

(Equation 1)

(Equation 2)

(Equation 3)

[0076]

[Table 2]

[0099] The catalyst of the example was higher in activity than the comparative example, and the effect of the present invention described later could be confirmed.

[0078]

The exhaust gas purifying catalyst according to claim 1 is
It has excellent heat resistance and can improve exhaust gas purification performance after durability.

The exhaust gas purifying catalyst according to claim 2 can more effectively exhibit high-temperature durability performance in addition to the above effects.

The exhaust gas purifying catalyst according to the third aspect can improve the poisoning resistance and prevent the formation of a noble metal alloy in addition to the above effects.

The exhaust gas purifying catalyst according to claim 4 can improve the initial performance in addition to the above effects.

The exhaust gas purifying catalyst according to the fifth aspect exhibits, in addition to the above-mentioned effects, more effective initial performance and high-temperature durability performance, and has no problem of peeling of the catalyst coat layer.

The exhaust gas purifying catalyst according to claim 6 can improve the thermal stability of alumina in addition to the above effects.

In the exhaust gas purifying catalyst according to the present invention, in addition to the above-mentioned effects, since the oxidation state of the noble metal is made suitable for purifying the exhaust gas, the catalytic performance of the noble metal can be prevented from lowering. The catalytic activity below can be further improved.

The exhaust gas purifying catalyst according to claim 8 can improve low-temperature activity and purifying performance after high-temperature durability in addition to the above effects. Furthermore, since the oxidation state of the noble metal is made suitable for purifying the exhaust gas, a decrease in the catalytic performance can be suppressed, and the catalytic activity and durability in a stoichiometric atmosphere can be improved.

The exhaust gas purifying catalyst according to the ninth aspect has, in addition to the above effects, a low-temperature activity and a reduction in reducing the noxious effect of HC adsorption and poisoning of a noble metal in a rich atmosphere. The activity in the atmosphere can be further improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomomi Eto 2 Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Inventor Shinji Yamamoto 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan

Claims (9)

[Claims] 1. A monolithic catalyst having a catalyst component-supporting layer, wherein silicon nitride (Si ₃ N ₄ ) is used as a catalyst component.
And / or boron nitride (BN) and silicon carbide (Si)
C), rhodium, and platinum and / or palladium. 2. The exhaust gas purifying catalyst according to claim 1, wherein the platinum and / or palladium-containing layer contains silicon nitride and / or boron nitride, and the rhodium-containing layer contains silicon carbide. Exhaust gas purification catalyst. 3. The exhaust gas purifying catalyst according to claim 2, wherein a platinum and / or palladium containing layer is disposed on an inner layer side and a rhodium containing layer is disposed on a surface layer side. . 4. The exhaust gas purifying catalyst according to claim 1, further comprising alumina powder. 5. The exhaust gas purifying catalyst according to claim 4, wherein the content ratio of the alumina powder to silicon nitride and / or boron nitride and silicon carbide is 3/7 to 8/2 in terms of powder weight ratio. An exhaust gas purifying catalyst characterized by the above-mentioned. 6. The exhaust gas purifying catalyst according to claim 4, wherein the alumina powder contains 1 to 10 mol% of at least one selected from the group consisting of cerium, zirconium and lanthanum in terms of metal. An exhaust gas purifying catalyst characterized by the above-mentioned. 7. The exhaust gas purifying catalyst according to claim 1, further comprising a metal selected from the group consisting of cerium, neodymium and lanthanum in a metal conversion of 1 to 40.
A catalyst for purifying exhaust gas, characterized in that it contains a zirconium oxide whose content is mol% and the remainder is zirconium. 8. The exhaust gas purifying catalyst according to claim 1, further comprising at least one metal selected from the group consisting of zirconium, neodymium and lanthanum in terms of metal.
A catalyst for purifying exhaust gas, characterized by containing cerium oxide containing 40 mol% and the balance being cerium. 9. The exhaust gas purifying catalyst according to claim 1, further comprising at least one selected from the group consisting of alkali metals and / or alkaline earth metals. Exhaust gas purification catalyst.