JPH09206599A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst for purification of exhaust gas having excellent heat resistance and improved purifying performance after the catalyst is used for a long time by incorporating silicon nitride or baron nitride, and rhodium, and platinum or palladium as the catalyst component in a monolithic catalyst having a layer which carries the catalyst component. SOLUTION: This catalyst for purification of exhaust gas has a monolithic structure having a layer which carries the catalyst component, and the catalyst contains at least one ceramic component selected from silicon nitride and baron nitride and at least one noble metal selected from rhodium, platinum and palladium as the catalyst component. The amt. of noble metals is about 0.1 to 15 g in 11 volume of the catalyst. The ceramic component sufficiently develops the catalytic activity of the noble metals as radicals. Moreover, it suppresses growing of grains of the base body and noble metals after the catalyst is used at high temp. for a long time and maintains dispersibility of these. Thereby, the catalyst has improved durability and shows excellent purifying performance in the initial stage and after long-term use at high a temp.

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 capable of efficiently purifying (NOx)) and having excellent purifying performance even after high temperature durability.

[0002]

2. Description of the Related Art Conventionally, exhaust gas purifying catalysts have not been sufficiently durable at high temperatures, and the catalyst deteriorates after high temperature durability, resulting in a marked reduction in purification performance. Development of an exhaust gas purification catalyst with excellent conversion performance is expected.

Conventionally, at least one of platinum, rhodium and palladium has been used as an active species of an automobile exhaust gas purification catalyst, and activated alumina having a high specific surface area has been widely used as a carrier for the active species. . However, conventionally used activated alumina has insufficient thermal stability, its crystal structure changes at high temperature, and a phase transition to α-alumina having a remarkably small BET specific surface area occurs. There is a problem in that the activity is unavoidable because the ring and aggregation are promoted, and the alumina undergoes a solid phase reaction with the noble metal to form an inactive compound. In view of this point, in recent years, measures have been taken to improve the durability of the catalyst by including in the catalyst a ceramic material that does not react with a noble metal to form an inactive compound and has high heat resistance. Came.

Techniques for incorporating a ceramic material into a catalyst include those disclosed in JP-A-59-52529 and JP-A-2-233146.

Japanese Patent Application Laid-Open No. 59-52529 discloses that γ-
There is disclosed a catalyst for purifying exhaust gas, which is highly active even at high temperatures, in which adhesion of the catalyst coating layer is improved by adding a metal and a ceramic whisker to alumina and the occurrence of cracks is suppressed.

JP-A-2-233146 discloses that by using Si ₃ N ₄ or SiC as a binder together with an organometallic compound of silicon, it is possible to suppress rearrangement and densification of zeolite particles, and to improve the high temperature even at high temperature. An active exhaust gas purification catalyst is disclosed.

[0007]

However, the above-mentioned Japanese Patent Application Laid-Open No.
In the catalysts described in JP-A 9-52529 and JP-A-2-233146, generation of cracks and densification of zeolite particles by adding ceramics such as Si ₃ N ₄ or SiC having excellent heat resistance to the catalyst. Although the suppression is attempted, there is a problem that sufficient heat resistance and purification performance cannot be obtained because the noble metal itself, which is a catalytically active species, is not stabilized or improved in durability.

Further, in the three-way catalyst, a SiC carrier is used as a carrier having excellent heat resistance instead of the conventional cordierite honeycomb carrier, or the difference in thermal conductivity between alumina and SiC is utilized to remove the catalyst from the catalyst layer. However, the heat resistance and catalyst performance have not been sufficiently improved. Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst that has improved durability as compared with conventional catalysts and that has excellent purification performance even at the initial stage and after high temperature durability.

[0009]

Means for Solving the Problems As a result of research to solve the above problems, the present inventors have selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and boron nitride (BN) as a catalyst component. By containing at least one, at least one selected from the group consisting of rhodium, platinum and palladium, and alumina powder, it was found that a catalyst having excellent purification performance even in the initial stage and after high temperature durability can be obtained, The present invention has been reached.

An exhaust gas purifying catalyst according to a first aspect of the present invention is an integral structure type catalyst having a catalyst component supporting layer, which comprises silicon nitride (Si ₃ N ₄ ) and boron nitride (BN) as catalyst components. It is characterized by containing at least one selected from the group and at least one selected from the group consisting of rhodium, platinum and palladium.

Further, in order to improve the initial performance of the exhaust gas purifying catalyst according to claim 1, the exhaust gas purifying catalyst according to claim 2 has the group consisting of the nitride powder and the rhodium, platinum and palladium. At least one selected from the above and alumina powder are contained.

Further, in order to prevent peeling of the catalyst coat layer of the exhaust gas purifying catalyst according to claim 1 or 2, the exhaust gas purifying catalyst according to claim 3 contains the nitride powder and the alumina powder. The ratio is 3/7 to 8/2 in powder weight ratio.

Furthermore, in order to further improve the catalytic activity of the exhaust gas purifying catalyst according to any one of claims 1 to 3 in a rich atmosphere, the exhaust gas purifying catalyst according to claim 4 further comprises oxygen. As an occlusion material, a zirconium oxide containing 1 to 40 mol% of metal selected from the group consisting of cerium, neodymium and lanthanum in terms of metal, and the balance of zirconium oxide containing 60 to 99 mol% of zirconium in terms of metal. Characterize.

Further, the exhaust gas purifying catalyst according to any one of claims 1 to 4 has low temperature activity and durability in a stoichiometric atmosphere and durability against poisonous substances such as lead (hereinafter referred to as "poisoning resistance"). The catalyst for purifying exhaust gas according to claim 5 further comprises an alumina containing 1 to 10 mol% of at least one selected from the group consisting of cerium, zirconium and lanthanum in terms of metal, and zirconium. A cerium oxide containing 1 to 40 mol% of metal selected from the group consisting of neodymium and lanthanum in terms of metal and 60 to 99 mol% of cerium in terms of metal as the balance thereof is contained.

Further, in order to improve the low temperature activity of the exhaust gas purifying catalyst according to claim 5 and the catalytic activity in a rich atmosphere, the exhaust gas purifying catalyst according to claim 6 further comprises an alkali metal and an alkaline earth. At least one selected from the group consisting of metal groups is contained.

As the ceramic component contained in the exhaust gas purifying catalyst of the present invention, the catalytic activity of the noble metal which is an active species is sufficiently exhibited, and further, the grain growth of the base material and the noble metal after high temperature durability is suppressed. In order to maintain these dispersibility, silicon nitride (Si ₃ N ₄ ) and boron nitride (BN), which have excellent heat resistance, are suitable.

The noble metal contained in the catalyst component supporting layer of the exhaust gas purifying catalyst of the present invention is at least one selected from the group consisting of rhodium, platinum and palladium. The content of these noble metals is 0.1 to 1 L of the catalyst.
It is 15 g. If the content of the noble metal is less than the specified value, low-temperature activity and purification performance are not sufficiently exhibited, and conversely, if it is more than that, the catalytic activity of the noble metal is saturated, which is not economically effective.

The exhaust gas purifying catalyst according to claim 2 is a catalyst component of the exhaust gas purifying catalyst according to claim 1, which is silicon nitride (Si ₃ N ₄ ) and / or boron nitride (B).
N) and at least one selected from the group consisting of rhodium, platinum and palladium, and further contains an alumina component. Compared to activated alumina, silicon nitride (S
Since i ₃ N ₄ ) and / or boron nitride (BN) have a small specific surface area and poor dispersibility of the noble metal at the initial stage, sufficient catalytic performance cannot be obtained. Therefore, by including activated alumina having a large specific surface area in the catalyst component layer, the dispersibility of noble metal and the diffusibility of gas at the initial stage are enhanced, and the low temperature activity and the catalyst performance are improved. Also, S, which has excellent heat resistance
By incorporating i ₃ N ₄ and BN, the grain growth of the base material and the noble metal after high temperature durability is suppressed, and the dispersibility of these is maintained to improve the performance after durability.

Further, in the exhaust gas purifying catalyst according to claim 3, the content ratio of the nitride powder and the alumina powder of the exhaust gas purifying catalyst according to claim 1 or 2 is 3 / in powder weight ratio. It is set to 7 to 8/2. If the amount of alumina is more than the specified value, the amount of Si ₃ N ₄ and / or BN is small, so that the effect of improving high temperature durability performance cannot be sufficiently obtained. When the amount of alumina is less than the specified value, the initial performance cannot be sufficiently obtained, and further, Si ₃ N
_Since the catalyst slurry of ₄ and / or BN lacks adhesion to the catalyst carrier, the catalyst coat layer is easily peeled off.

Further, an exhaust gas purifying catalyst according to a fourth aspect is a catalyst selected from the group consisting of cerium, neodymium and lanthanum, in addition to the catalyst component of the exhaust gas purifying catalyst according to any one of the first to third aspects. It contains zirconium oxide containing one selected. The zirconium oxide contains a zirconium oxide containing one element selected from the group consisting of cerium, neodymium, and lanthanum in an amount of 1 to 40 mol% in terms of metal, and the balance of 60 to 99 mol% in terms of zirconium in terms of metal. It is what is done. 1
-40 mol% is the zirconium oxide (ZrO
₂ ) is added with at least one element selected from the group consisting of cerium, neodymium and lanthanum, and ZrO ₂
This is to significantly improve the oxygen releasing ability, the BET specific surface area, and the thermal stability. When it is less than 1 mol%, it is the same as the case of only ZrO ₂ , and the effect of adding the above elements does not appear,
If it exceeds 40 mol%, this effect is saturated or diminished.

By containing the zirconium oxide powder containing at least one selected from the group consisting of cerium, neodymium and lanthanum in the catalyst component supporting layer, zirconium oxide having a high oxygen storage capacity can be obtained in a rich atmosphere and near stoichiometry. Since the lattice oxygen and the adsorbed oxygen are released to make the oxidation state of the noble metal suitable for purifying the exhaust gas, it is possible to suppress deterioration of the catalytic performance of the noble metal.

The exhaust gas purifying catalyst according to claim 5 further contains alumina in addition to the catalyst component of the exhaust gas purifying catalyst according to any one of claims 1 to 4. In particular, in order to enhance the structural stability of alumina after high-temperature durability and suppress the phase transition to α-alumina and the decrease in BET specific surface area, the alumina is at least selected from the group consisting of cerium, zirconium and lanthanum. One kind is contained at 1 to 10 mol% in terms of metal. If it is less than 1 mol%, a sufficient addition effect cannot be obtained, and if it exceeds 10 mol%, the addition effect is saturated. The amount of such alumina used is 10 to 200 g per 1 L of the catalyst. If the amount is less than 10 g, sufficient dispersibility of the noble metal cannot be obtained, and if the amount is more than 200 g, the catalytic performance is saturated, and no remarkable improvement effect is obtained.

Furthermore, the exhaust gas purifying catalyst according to claim 5 contains cerium oxide in addition to the above catalyst components. The cerium oxide contains 1 to 40 mol% of metal selected from the group consisting of zirconium, neodymium and lanthanum in terms of metal, and the balance thereof contains cerium oxide containing 60 to 99 mol% of cerium in terms of metal. Is. By containing cerium oxide,
The cerium oxide, which has a high oxygen storage capacity, releases lattice oxygen and adsorbed oxygen in a rich atmosphere and in the vicinity of stoichiometry, making the oxidation state of the noble metal suitable for purifying exhaust gas and suppressing deterioration of catalyst performance. The amount of 1 to 40 mol% is determined by adding at least one element selected from the group consisting of zirconium, neodymium and lanthanum to cerium oxide (CeO ₂ ), and thereby the oxygen releasing ability of CeO ₂ and the BET specific surface area. ,
This is to significantly improve the thermal stability. 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, in the exhaust gas purifying catalyst according to claim 6, the alkali metal and / or alkaline earth metal used include lithium, sodium, potassium, cesium, magnesium, 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 in a reducing atmosphere can be further improved. . The content is 1 to 40 g in 1 L of the catalyst. 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, at least one selected from the group consisting of rhodium, platinum and palladium is used as Si ₃ N ₄ and / or B.
The method of supporting N and / or 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 compound such as dinitrodiammine acid salt, chloride and nitrate.

Water can be removed by, for example, a filtration method or an evaporation dryness method.
It can be performed by appropriately selecting from among known methods.
Noble metal-supported alumina used in the present invention, and noble metal-supported alumina
Si _ThreeN_FourAnd / or first heat treatment to obtain BN
Is not particularly limited, but the added precious metal has good dispersibility.
In order to support, relatively low temperature of 400 ℃ ~ 800 ℃
It is preferable to carry out firing in air and / or under air circulation.
Good.

Furthermore, Si ₃ N ₄ and / or BN and / or alumina powder may be added as a plain substance without supporting a noble metal. Further, preferably, 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 cerium oxide containing at least one selected from the group consisting of zirconium, neodymium and lanthanum to alumina powder or zirconium oxide powder, the oxidation state of the noble metal in a reducing atmosphere. Can be more effectively maintained in a state suitable for exhaust gas purification.

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

Specifically, at least one of Si ₃ N ₄ and BN, at least one selected from the group consisting of rhodium, platinum and palladium, alumina powder, zirconium oxide powder, and cerium oxide. Alumina sol is added to the product powder and wet pulverized to form a slurry, which is adhered to a catalyst carrier and calcined at a temperature in the range of 400 to 650 ° C. in the air and / or under the air flow.

The catalyst carrier can be appropriately selected and used from known catalyst carriers, and examples thereof include a monolith carrier and 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, a cordierite material such as ceramic is 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 total amount of the catalyst component coating layer adhered to the honeycomb material is preferably 50 g to 400 g per 1 L of the catalyst as a total amount of the 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 develop the synergistic effect of rhodium and platinum and / or palladium, the catalyst component layer containing platinum and / or palladium is arranged under the coat layer (inner layer side), and rhodium is added. The contained catalyst component layer is arranged 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, potassium, cesium, magnesium, calcium,
It is at least one element selected from the group consisting of strontium and barium.

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

That is, an aqueous solution of a powder of an alkali metal and / or alkaline earth metal compound is impregnated into the above carrier carrying a washcoat component, dried, and then dried in air and / or under air flow to 200-600. It is baked at a relatively low temperature of ℃. When the firing temperature is 20
If the temperature is lower than 0 ° C, the alkali metal and alkaline earth metal compounds cannot be sufficiently converted into the oxide form, and conversely 600 ° C.
Even if it exceeds, the effect of the firing temperature is saturated, and a significant difference cannot be obtained.

[0039]

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 dinitrodiamine platinum or sprayed under high-speed stirring to obtain 150 ° C.
After drying for 24 hours at 400 ° C for 1 hour, then 60
Pt-supported alumina powder (powder A) after firing at 0 ° C for 1 hour
I got The Pt concentration of this powder A was 1.1% by weight. Alumina powder containing 3% by weight of Zr was impregnated with an aqueous solution of rhodium nitrate or sprayed under high-speed agitation, and the temperature was adjusted to 2 at 150 ° C.
After drying for 4 hours, 400 ℃ for 1 hour, then 600 ℃
Then, it was calcined for 1 hour to obtain Rh-supported alumina powder (powder B). The Rh concentration of this powder B was 1.7% by weight. S
The i ₃ N ₄ powder was impregnated with a rhodium nitrate aqueous solution or sprayed under high-speed stirring and dried at 150 ° C. for 24 hours, and then 40
Firing was performed at 0 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Rh-supported Si ₃ N ₄ powder (powder C). The Rh concentration of this powder C was 1.0% by weight.

Pt-supported alumina powder A147 g, Z
124 g of cerium oxide powder carrying 30% by weight of r, and 229 g of nitric acid acidic alumina sol (boehmite alumina 1
The sol obtained by adding 10 wt% nitric acid to 0 wt% was put into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. 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. Do this work twice, coat layer weight 200g / L
-Support catalyst-A was obtained. Rh-supported Si ₃ N ₄ powder C
67 g, the above Rh-supported alumina powder B 38 g, 111 g of zirconium oxide powder containing 30% by weight of Ce, 28 g of alumina powder containing 3% by weight of Zr, and 256 g of nitric acid-acidified alumina sol were charged into a magnetic ball mill, mixed and pulverized, and Rh-supported Si ₃ A slurry liquid was obtained in which the content ratio of the N ₄ powder C and the alumina-based powder was 1/1 by weight. 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.
The catalyst was obtained by baking at 0 ° C. for 1 hour and applying a coat layer weight of 45 g / L. The cerium oxide powder and the alumina powder may contain lanthanum, neodymium and the like.
Then, a barium acetate solution was adhered to the above-mentioned catalyst component-supporting cordierite monolithic carrier, followed by firing at 400 ° C. for 1 hour to contain BaO in an amount of 20 g / L. Further, after applying a potassium acetate solution by the same procedure, 4
It was calcined at 00 ° C. for 1 hour to contain 1 g / L as K ₂ O.

Example 2 Using the BN powder, an Rh-supporting BN powder (powder D) was prepared in the same manner as the powder C, and instead of the powder C in the catalyst production,
An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that the powder D was used.

Example 3 An alumina powder carrying 1.96% by weight of Rh (powder E) was prepared in the same manner as the powder B, and 67 g of this Rh-supporting alumina powder E, 67 g of Si ₃ N ₄ powder, and 30% of Ce were added. % Of zirconium oxide powder and 256 g of nitric acid-acidified alumina sol are put into a magnetic ball mill, mixed and pulverized, and the content ratio of Si ₃ N ₄ powder and alumina-based powder is 1/1 by weight. Got An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that this slurry liquid was attached to the above coated catalyst-A.

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 Alumina powder containing 3 mol% of Ce was impregnated with an aqueous solution of dinitrodiaminepalladium or sprayed under high-speed stirring,
After drying at 150 ° C. for 24 hours, it was baked at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain a Pd-supported alumina powder (powder F). The Pd concentration of this powder F was 1.7% by weight. The powder F may contain lanthanum, zirconium, neodymium, or the like. Si ₃ N ₄ powder,
Dinitrodiamine palladium aqueous solution is impregnated or sprayed under high speed stirring and dried at 150 ° C for 24 hours, then 400
Firing at 1 ° C. for 1 hour and then at 600 ° C. for 1 hour gave Pd-supported Si ₃ N ₄ powder (powder G). The Pd concentration of this powder G was 1.7% by weight. Zr was added to a cerium oxide powder supporting 30% by weight of an aqueous dinitrodiaminepalladium solution or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, and then calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour, A Pd-supporting cerium oxide powder (powder H) was obtained. The Pd concentration of this powder H was 0.75% by weight.

Pd-supported alumina powder F73 g, Pd-supported Si ₃ N ₄ powder G73 g, Pd-supported cerium oxide powder H100 g, and nitric acid-acidified alumina sol 254 g (10% by weight of boehmite alumina 10% by weight).
The sol obtained by adding the nitric acid was added to a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. 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 B having a coat layer weight of 200 g / L and a carrier. Rh-supported alumina powder B was used in place of Rh-supported Si ₃ N ₄ powder C, Si ₃ N ₄ was not used in the catalyst slurry, and this slurry was attached to the catalyst B instead of catalyst A. In the same manner as in Example 1, an exhaust gas purification catalyst was obtained.

Example 6 BN powder was impregnated with an aqueous dinitrodiaminepalladium solution or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, and then calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to support Pd. BN powder (powder I) was obtained. The Pd concentration of this powder I was 1.7% by weight. Instead of powder G,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 5, except that the Pd-supported BN powder I was used.

Example 7 An alumina powder (powder J) carrying 3.4% by weight of Pd was prepared in the same manner as the powder F, and 73 g of this Pd-supporting alumina powder J, 73 g of Si ₃ N ₄ powder, and 30 weight of Ce were prepared. %
100 g of zirconium oxide powder containing and 254 g of nitric acid acidic alumina sol were put into a magnetic ball mill, mixed and pulverized, and a slurry liquid in which the content ratio of Si ₃ N ₄ powder and alumina-based powder was 1/1 by weight ratio was obtained. Obtained. An exhaust gas purification catalyst was obtained in the same manner as in Example 5, except that a catalyst having a coat layer weight of 200 g / L-support was obtained using this slurry liquid.

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.

Example 9 Pd-supported alumina powder F146g, Pd-supported cerium oxide powder H100g, and nitric acid-acidified alumina sol 254g (sol obtained by adding 10 wt% nitric acid to 10 wt% boehmite alumina) The mixture was put into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid.
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-C having a coat layer weight of 200 g / L and a carrier.

67 g of Rh-supported Si ₃ N ₄ powder C, 38 g of Rh-supported alumina powder B, 111 g of zirconium oxide powder containing 30% by weight of Ce, 29 g of alumina powder containing 3% by weight of Zr, and nitric acid-acidified alumina sol 2
56g is put into a magnetic ball mill, mixed and pulverized, and Rh
A slurry liquid was obtained in which the content ratio of the supported Si ₃ N ₄ powder C and the alumina powder was 1/1 by weight. This slurry liquid is attached to the above-mentioned coated catalyst-C, the excess slurry in the cell is removed by an air flow and dried, and the temperature is 400 ° C.
The coating layer was baked for 1 hour at a coating layer weight of 45 g / L to obtain a catalyst. The cerium oxide powder and the alumina powder may contain lanthanum, neodymium and the like. Then
After the barium acetate solution was attached to the above-mentioned catalyst component-supporting cordierite monolithic carrier, it was baked at 400 ° C. for 1 hour to contain BaO in an amount of 20 g / L. Furthermore, after adhering the potassium acetate solution by the same procedure, 400 ° C
Calcination was carried out for 1 hour to contain 1 g / L as K ₂ O.

Example 10 An exhaust gas purifying catalyst was obtained in the same manner as in Example 9 except that Rh-supporting BN powder D was used instead of Rh-supporting Si ₃ N ₄ powder C in the catalyst production.

Example 11 67 g of the above Rh-supported alumina powder E, 6 Si ₃ N ₄ powder 6
Zirconium oxide powder 1 containing 7 g and 30 wt% Ce
11 g and 256 g of nitric acid-acidified alumina sol were put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid in which the content ratio of Si ₃ N ₄ powder and alumina-based powder was 1/1 by weight ratio. The slurry liquid is used as the above-mentioned catalyst-
An exhaust gas purification catalyst was obtained in the same manner as in Example 9 except that the catalyst was attached to C.

Example 12 An exhaust gas purifying catalyst was obtained in the same manner as in Example 9 except that BN powder was used instead of Si ₃ N ₄ powder.

Comparative Example 1 The same as Example 1 except that Rh-supported alumina powder B was used instead of Rh-supported Si ₃ N ₄ powder C and that Si ₃ N ₄ was not used in the catalyst slurry. As a result, an exhaust gas purifying catalyst was obtained.

Comparative Example 2 Exhaust gas purification in the same manner as in Example 1 except that a slurry liquid in which the content ratio of Rh-supported Si ₃ N ₄ powder C and alumina-based powder was 3/7 by weight ratio was obtained. A catalyst for use was obtained.

Comparative Example 3 Exhaust gas purification in the same manner as in Example 1 except that a slurry liquid in which the content ratio of the Rh-supported Si ₃ N ₄ powder C and the alumina-based powder was 8/2 by weight ratio was obtained. A catalyst for use was obtained.

Comparative Example 4 The procedure of Example 5 was repeated, except that the Pd-supported alumina powder F was used in place of the Pd-supported Si ₃ N ₄ powder G and that Si ₃ N ₄ was not used in the catalyst slurry. An exhaust gas purification catalyst was obtained.

In the exhaust gas purifying catalysts obtained in Examples 1 to 12 and Comparative Examples 1 to 4, various noble metals, various base materials, weight ratios of nitride and alumina, and alkaline earth metals and alkali metals. The content is shown in Table 1.

[0060]

[Table 1]

Test Examples The exhaust gas purifying catalysts of Examples 1 to 12 and Comparative Examples 1 to 4 were evaluated for catalytic activity under the following evaluation conditions. For the activity evaluation, a catalyst was attached to a 4500 cc engine manufactured by Nissan Motor Co., Ltd., the durability was evaluated under the following durability conditions, and then the activity was evaluated under the following activity evaluation conditions.

[0062]

[0063]

The conversion performance (%) of each HC, CO and NO _x in stoichiometry determined by the following _equations 1 to 3 is used to determine the purifying performance of each exhaust gas purifying catalyst at the initial stage and after endurance.
And the results are shown in Table 2.

[0065]

[Equation 1]

[Equation 2]

(Equation 3)

[0066]

[Table 2]

In Examples, compared with Comparative Examples, the catalytic activity was higher, and the effects of the present invention described later could be confirmed.

[0068]

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

In addition to the above effects, the exhaust gas purifying catalyst according to claim 2 can improve the initial performance.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 3 more effectively exhibits initial performance and high temperature durability performance, and there is no problem of peeling of the catalyst coating layer.

In addition to the above effects, the catalyst for purifying exhaust gas according to claim 4 makes the oxidation state of the noble metal suitable for purifying exhaust gas, so that the reduction of the catalytic activity of rhodium can be suppressed.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 5 can improve low temperature activity and purification performance after high temperature endurance. Furthermore, since the oxidation state of the noble metal is suitable for purification of exhaust gas, it is possible to suppress deterioration of catalyst performance.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 6 mitigates the HC adsorption poisoning effect in a rich atmosphere, and suppresses sintering of noble metals, so that it has low temperature activity and reduction. The activity in the atmosphere can be further improved.

Further, SiN and BN have various crystal structures such as α-type, β-type, hexagonal crystal and tetragonal crystal. It was confirmed that the present invention can obtain the above effects regardless of the crystal structure.

 ──────────────────────────────────────────────────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 (6)

[Claims] 1. A monolithic structure type catalyst having a catalyst component supporting layer, wherein at least one selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and boron nitride (BN) is used as a catalyst component, rhodium, platinum and An exhaust gas purifying catalyst comprising at least one selected from the group consisting of palladium. 2. The exhaust gas purifying catalyst according to claim 1, containing the nitride powder, at least one selected from the group consisting of rhodium, platinum and palladium, and alumina powder. Exhaust gas purification catalyst. 3. The exhaust gas purifying catalyst according to claim 1 or 2, wherein the content ratio of the nitride powder and the alumina powder is in the range of 3/7 to 8/2 in powder weight ratio. A characteristic exhaust gas purification catalyst. 4. The exhaust gas purifying catalyst according to claim 1, further comprising 1 to 40 in terms of metal of one selected from the group consisting of cerium, neodymium and lanthanum.
Mol%, zirconium as the balance 60% in terms of metal
An exhaust gas purifying catalyst, which contains zirconium oxide in an amount of about 99 mol%. 5. An alumina containing the exhaust gas purifying catalyst according to claim 1 and further containing at least one selected from the group consisting of cerium, zirconium and lanthanum in a metal amount of 1 to 10 mol%. And 1 to 40 mol% of metal selected from the group consisting of zirconium, neodymium and lanthanum in terms of metal, and the balance thereof contains cerium oxide containing 60 to 99 mol% of cerium in terms of metal. Exhaust gas purification catalyst. 6. The exhaust gas purifying catalyst according to claim 5,
Further, the exhaust gas purifying catalyst is characterized by containing at least one selected from the group consisting of alkali metals and alkaline earth metals.