JPH11226405A - Catalyst for purification of exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a catalyst for purification of exhaust gas having enhanced durability as compared with a conventional catalyst and having excellent low temp. activity and purifying performance even after use over a long period of time. SOLUTION: The catalyst is a monolithic catalyst with a layer that carries catalyst components including at least palladium and a powdery metallic aluminate. This metallic aluminate is an alumina-base multiple oxide represented by the formula [Y]d Zna Alb Oc [where Y is cerium and/or zirconium, (a), (b), (c) and (d) show the atomic ratio among the elements, in the case of b=2.0, 0.1<=a<=0.6 and 0.01<=d<=0.3, and (c) is the number of oxygen atoms required to satisfy the valences of the other components].

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 a method for producing the same, and more particularly to a hydrocarbon (hereinafter referred to as "HC") in exhaust gas discharged from an internal combustion engine of an automobile or the like.
Exhaust gas that can efficiently purify carbon monoxide (hereinafter, referred to as “CO”) and nitrogen oxides (hereinafter, referred to as “NO _x ”), and has excellent purification performance even after durability. The present invention relates to a purification catalyst and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, exhaust gas purifying catalysts for automobiles are composed of a reducing component containing hydrocarbons and oxygen (hereinafter referred to as oxygen).
(Hereinafter referred to as “O ₂ ”) and oxidizing components including NO _x have a high purification performance for exhaust gas containing a ratio close to the stoichiometric ratio, but after endurance, the purification performance is significantly reduced. A large amount of precious metal is used so that high purification performance can be maintained from the beginning to the end of durability.

[0003] Such exhaust gas purifying catalysts are disclosed, for example, in JP-A-62-262841 and JP-A-4-284.
847, JP-A-6-378 and JP-A-7-378
There is one disclosed in Japanese Patent No. 60118.

Japanese Unexamined Patent Publication (Kokai) No. 62-282641 discloses an exhaust gas purifying catalyst in which rhodium is supported on zirconium oxide. Specifically, zirconium oxide containing rhodium, activated alumina, cerium oxide Is obtained by attaching, drying and calcining a slurry containing silica and alumina sol, and then supporting platinum.

Japanese Patent Application Laid-Open No. 4-284847 discloses that in addition to those conventionally used as catalyst components, such as platinum, rhodium, activated alumina and cerium oxide, cerium oxide, lanthanum, praseodymium, yttrium, neodymium, An exhaust gas purifying catalyst is disclosed, which is combined with a zirconium compound stabilized by one or more metal oxides selected from the group consisting of Group 2A and Group 3B.

JP-A-6-378 discloses that activated alumina and cerium oxide are selected from the group consisting of at least one of platinum and palladium as catalyst components and potassium, cesium, strontium and barium as basic elements. There has been proposed an exhaust gas purifying catalyst in which at least one kind of metal oxide is supported. That is, the catalyst is a platinum group element, activated alumina, cerium oxide or the like,
In addition to those conventionally used as catalyst components, at least one of potassium compounds, cesium compounds, strontium compounds and barium compounds, which are basic elements, is combined.

Japanese Patent Application Laid-Open No. 7-60118 discloses a zirconium oxide stabilized with yttria, calcia, magnesia or scandia and 40 to 95% by weight of alumina or titania, and a surface area of 30 to 300 m ² / g. Noble metal catalysts using an oxygen ion conductive composite having the above as a supporting substrate of rhodium / platinum or rhodium / palladium have been proposed.

[0008]

However, the conventional catalyst described in the above publication uses a large amount of a noble metal in order to maintain high purification performance from the initial stage to the end of the durability. For this reason, as a three-way catalyst for purifying exhaust gas, a catalyst that can obtain high purification performance even when the amount of noble metal used is small is desired. However, when the amount of the noble metal is reduced, there is a problem that the durability at high temperatures is insufficient, and after the durability, the catalytic activity and purification performance in a low temperature region are deteriorated.

This is based on a stoichiometric air-fuel ratio (hereinafter referred to as "stoichiometric") and a reducing atmosphere (hereinafter, referred to as "stoichiometric") having an insufficient oxygen concentration.
Under the exhaust gas atmosphere of automobiles whose composition changes widely from an oxidizing atmosphere (hereinafter referred to as "lean") to an oxidizing atmosphere having an excessively high oxygen concentration (hereinafter referred to as "lean"), deterioration (sintering) of noble metal species is promoted. As a result, it is considered that the purification performance is reduced. In particular, when reducing the amount of precious metals,
There has been a problem that the above-mentioned effects appear remarkably and the purification performance is further reduced.

Alumina has insufficient thermal stability, changes its crystal structure at high temperatures, and causes a phase transition to α-alumina having a very small BET specific surface area. At this time,
Sintering of the noble metal is promoted, and alumina causes a solid phase reaction with the noble metal to form an inactive compound. As a result, purification performance is greatly reduced. On the other hand, zirconium oxide is excellent in structural stability, but has a drawback that it is difficult to obtain sufficient low-temperature activity and purification performance from the initial stage to the end of durability due to poor dispersibility of noble metal species due to a small BET specific surface area.

Accordingly, it is an object of the present invention to provide a catalyst for purifying exhaust gas, which has higher durability than conventional catalysts and has excellent low-temperature activity and purification performance even after durability, and a method for producing the same. .

[0012]

Means for Solving the Problems As a result of research for solving the above problems, the present inventors have found that an alumina-based composite oxide containing a transition metal element in a fixed composition ratio together with palladium in a catalyst component-supporting layer is obtained. The present inventors have found that the low-temperature activity and the purification performance after durability are remarkably improved / maintained by the addition, and have reached the present invention.

The exhaust gas purifying catalyst according to the first aspect of the present invention is an integrated catalyst having a catalyst component-supporting layer, wherein at least palladium and a metal aluminate powder are contained as catalyst components, and the metal aluminate powder is used as a catalyst. , The following general formula:

[Y] _d Zn _a Al _b O _c (wherein Y is cerium and / or zirconium, a, b, c and d represent the atomic ratio of each element, and b
= 2.0, a = 0.1-0.6, d = 0.01-
0.3 and c are the number of oxygen atoms necessary to satisfy the valence of each component described above).

In order to further enhance the durability and catalytic activity of the exhaust gas purifying catalyst according to the first aspect, the exhaust gas purifying catalyst according to the second aspect is further selected from the group consisting of lanthanum, neodymium and zirconium. 1 to 40 mol% of at least one metal in terms of metal;
Cerium oxide containing 0 to 98 mol% is contained in the exhaust gas purifying catalyst.

Further, in order to further enhance the low-temperature activity of the exhaust gas purifying catalyst according to the first or second aspect, the exhaust gas purifying catalyst according to the third aspect includes the total amount of palladium contained in the catalyst component supporting layer. 30% to 80% by weight of palladium in terms of metal is contained in the alumina-based composite oxide.

Further, in order to further enhance the HC purifying performance of the exhaust gas purifying catalyst according to any one of claims 1 to 3 in a rich region, the exhaust gas purifying catalyst according to claim 4 further comprises rhodium. Preferably, it is contained in the exhaust gas catalyst.

Furthermore, in order to further enhance the durability and catalytic activity of the exhaust gas purifying catalyst according to claim 4, the exhaust gas purifying catalyst according to claim 5 is further selected from the group consisting of lanthanum, neodymium and cerium. 1 to 40 mol% of at least one metal in terms of metal, and 6% in terms of metal in zirconium.
It is preferable that zirconium oxide containing 0 to 98 mol% is contained in the exhaust gas catalyst.

Furthermore, exhaust gas purification according to claim 4 or 5
NO in rich region _xHigher purification performance
The exhaust gas purifying catalyst according to claim 6 is
The rhodium-containing layer is the same layer and / or
It is characterized in that it is arranged above the radium-containing layer.

Furthermore, in order to improve _the NO _x purification performance at low temperature activity and a rich range of an exhaust gas purifying catalyst of claims 1 to 6, wherein any one of claims, the exhaust gas purifying catalyst according to claim 7, wherein the And at least one selected from the group consisting of alkali metals and alkaline earth metals is contained in the exhaust gas catalyst.

Further, in the method for producing an exhaust gas purifying catalyst according to the present invention, in producing the alumina-based composite oxide according to any one of claims 1 to 7, fine particle alumina hydrate colloid and zinc And after dissolving or dispersing a water-soluble salt of cerium and / or zirconium in water, 1 to 10
It is characterized in that it is obtained by heating to 50 to 200 ° C. by pressurizing to atmospheric pressure, removing moisture, drying and then firing.

Further, in the method for producing an exhaust gas purifying catalyst according to the ninth aspect, in producing the alumina-based composite oxide according to any one of the first to seventh aspects, boehmite alumina, zinc, cerium and At least one aqueous solution selected from the group consisting of formic acid, acetic acid, and succinic acid is added to a mixed solution obtained by dissolving or dispersing a water-soluble salt of zirconium in water to adjust the pH to 3.0 to 7.0. It is characterized by being obtained by adjusting the pressure to a range, heating to 50 to 200 ° C. by pressurizing to 1 to 10 atm, removing moisture, drying, and then firing.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The noble metal contained at least in the catalyst component supporting layer of the exhaust gas purifying catalyst of the present invention is palladium. The content of the palladium is 0.01 to 10 g / L in 1 L of the catalyst. If the amount is less than 0.01 g, the low-temperature activity and the purification performance are not sufficiently exhibited. Conversely, if the amount exceeds 10 g, the dispersibility of palladium is deteriorated, the catalyst performance is not significantly improved, and it is not economically effective.

The composition of the metal aluminate in the catalyst component is represented by the following general formula:

[Y] _d Zn _a Al _b O _c (where Y is cerium and / or zirconium, a, b, c and d represent the atomic ratio of each element, b
= 2.0, a = 0.1-0.6, d = 0.01-
0.3 and c are the number of oxygen atoms necessary to satisfy the valence of each of the above components).

In order to enhance the low-temperature activity and purification performance of palladium, cerium and / or
Or zirconium is contained. The amount of the alumina-based composite oxide used is 10 to 200 g per liter of the catalyst. If the amount is less than 10 g, a sufficient effect of improving the catalytic performance that the alumina-based composite oxide activates palladium cannot be obtained, and even if the amount exceeds 200 g, the effect of improving the catalytic performance is saturated or, conversely, the catalytic performance decreases. Can be

When a is less than 0.1, the effect of Zn added to the alumina-based composite oxide is small, so that a sufficient improvement effect cannot be obtained, and it is not different from alumina (Al ₂ O ₃ ). On the other hand, if a exceeds 0.6, it becomes difficult to form a composite oxide in which Zn is completely dissolved in the alumina-based composite oxide, and physical properties such as thermal stability are deteriorated. Sufficient performance cannot be obtained in the early stage.

If d is less than 0.01, the effect of cerium and / or zirconium added to the alumina-based composite oxide is small and a sufficient improvement effect cannot be obtained, and the alumina-based composite oxide (Zn _a Al ₂ O) _{Same as c} ). Also, d
= 0.3, it becomes difficult to form an alumina-based composite oxide in which cerium and / or zirconium is dissolved, and B
Since physical properties such as the ET specific surface area are reduced, sintering of palladium cannot be suppressed during durability, and performance after durability deteriorates.

As described above, by using an alumina-based composite oxide having a specific composition ratio, structural stability and specific surface area at a high temperature are sufficient as compared with stoichiometric metal aluminate.
The added element forms a solid solution in the crystal structure of alumina and does not exist as an oxide on the surface, so that sufficient performance can be obtained.

The exhaust gas purifying catalyst according to the second aspect further includes cerium oxide in addition to the catalyst components in the exhaust gas purifying catalyst according to the first aspect. The cerium oxide contains at least one element selected from the group consisting of lanthanum, neodymium, and zirconium in an amount of 1 to 40 mol% in terms of metal and 60 to 98 mol% of cerium. The reason for setting the content to 1 to 40 mol% is that at least one element selected from the group consisting of lanthanum, neodymium and zirconium is added to cerium oxide (CeO ₂ ), and the oxygen releasing ability of cerium oxide and BET
This is for remarkably improving the specific surface area and the thermal stability. If it is less than 1 mol%, it is not different from the case of only cerium oxide,
The effect of adding the lanthanum and / or neodymium and / or zirconium elements does not appear, and if it exceeds 40 mol%, this effect is saturated or conversely decreases.

As described above, since the cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium is further contained in the catalyst component supporting layer, the cerium oxide having a high oxygen storage capacity is reduced. (Oxygen deficiency) Since lattice oxygen and adsorbed oxygen are released in the atmosphere and near the stoichiometric air-fuel ratio to make the oxidation state of palladium suitable for purifying exhaust gas, it is possible to suppress a decrease in catalytic ability due to reduction of palladium. . Further, by contact with the alumina-based composite oxide in the catalyst component supporting layer,
It is also possible to suppress a decrease in catalytic ability due to the reduction of the alumina-based composite oxide.

Further, the exhaust gas purifying catalyst according to claim 3 is the catalyst component in the exhaust gas purifying catalyst according to claim 1 or 2, wherein the total palladium amount is from 30 to 30 in terms of metal.
80% by weight of palladium is supported on an alumina-based composite oxide powder containing cerium and / or zirconium.

As a substrate on which palladium is supported, in order to increase the dispersibility of palladium and improve the catalytic performance,
Metal aluminates, especially alumina-based composite oxides, are suitable. In particular, palladium sintering can be suppressed because the structural stability of alumina after high-temperature durability is enhanced and the phase transition to α-alumina and a decrease in the BET specific surface area are suppressed.

By supporting palladium on the alumina-based composite oxide powder, the alumina-based composite oxide powder containing cerium and / or zirconium and the palladium come into close contact with each other, and the lattice oxygen in the alumina-based composite oxide and the surface Adsorbed oxygen is easily transferred and released via palladium, which improves the low-temperature activity of palladium, and improves the purification performance from the initial stage to after the endurance. Also, cerium and / or zirconium are dissolved in the alumina-based composite oxide, effectively function as adsorption active points such as NO _x, to improve the catalytic performance of the palladium in an oxygen deficient atmosphere and near stoichiometric air-fuel ratio It will be.

When the amount of palladium supported on the alumina-based composite oxide powder containing cerium and / or zirconium is less than 30% by weight, the effect of improving the low-temperature activity is not sufficiently exhibited, and conversely, the amount exceeds 80% by weight. In addition, the effect of improving the NO _x steady conversion performance is saturated and is not effective.

As described above, by supporting 30 to 80% by weight of palladium in terms of metal in the total amount of palladium contained in the catalyst component-supporting layer on the alumina-based composite oxide, the effect of improving the low-temperature activity of palladium is improved. NO _x steady turning performance improving effect and can be obtained sufficiently.

The catalyst for purifying exhaust gas according to claim 4 can further contain rhodium in the catalyst component supporting layer. The content of rhodium is 0.01 to 5 g per 1 L of the catalyst. If the content is less than 0.01 g, the poisoning resistance and the purification performance in the rich region are not sufficiently exhibited.
If the temperature exceeds the limit, the catalytic activity of rhodium is saturated, and it is not economically effective.

As the substrate on which the rhodium is supported,
In order to increase the dispersibility of rhodium and improve catalyst performance,
Alumina containing zirconium oxide is suitable.
In particular, since the dispersibility of rhodium after high-temperature durability can be enhanced and the formation of a compound between rhodium and alumina can be suppressed, a decrease in rhodium performance can be suppressed.

The rhodium-supported powder is contained in the palladium / alumina-based composite oxide powder and, if necessary, a catalyst component-supporting layer containing cerium oxide to purify the catalyst at low temperature activity and in an oxygen-deficient atmosphere. The performance can be further improved.

Further, the exhaust gas purifying catalyst according to the fifth aspect further comprises a zirconium oxide in addition to the catalyst components in the exhaust gas purifying catalyst according to the fourth aspect. The zirconium oxide contains at least one element selected from the group consisting of lanthanum, neodymium and cerium in an amount of 1 to 40 mol% in terms of metal, and zirconium as 60%.
９８98 mol%. The reason for setting the content to 1 to 40 mol% is that zirconium oxide (ZrO ₂ ) contains lanthanum,
This is because at least one element selected from the group consisting of neodymium and cerium is added to remarkably improve the oxygen storage capacity, BET specific surface area, and thermal stability of zirconium oxide. If it is less than 1 mol%, the effect of adding the lanthanum and / or neodymium and / or cerium elements does not appear as in the case of only zirconium oxide, and 40 mol%
If it exceeds 3, it becomes difficult to form a composite oxide in which the added element is completely dissolved in the zirconium oxide, and the physical properties of the zirconia oxide such as thermal stability deteriorate.

As described above, the zirconium-containing alumina powder supporting rhodium and, if necessary, the zirconium-containing alumina powder-containing catalyst component-supporting layer further include lanthanum, neodymium and cerium. By containing the zirconium oxide containing at least one selected element, the oxidation state of rhodium is made suitable for purifying exhaust gas, and therefore, a decrease in catalytic ability due to reduction of rhodium can be suppressed.

Further, in the exhaust gas purifying catalyst according to the present invention, the rhodium-containing catalyst component layer is formed of the same layer as the palladium-containing layer and / or the palladium-containing catalyst in order to efficiently exhibit the synergistic action of palladium and rhodium. It is arranged above the catalyst component layer. As a result, it is possible to sufficiently secure the poisoning resistance to poisonous substances such as lead and sulfur and the purification performance in a rich region.

Further, the exhaust gas purifying catalyst according to claim 7 further contains at least one selected from the group consisting of alkali and alkaline earth metals. The alkali and alkaline earth metals used include lithium, potassium, cerium, magnesium, calcium, strontium and barium. Its content is 2 to 30 g per liter of catalyst. If the amount is less than 2 g, the poisoning resistance and the purification performance in the rich region are not sufficiently exhibited, and if it exceeds 30 g, the effect of addition is saturated and is not economically effective.

The palladium, alumina-based composite oxide powder, and cerium oxide and zirconium oxide, which are added as required, are brought into close contact with the alkali metal and / or alkaline earth metal, thereby improving the purification performance. Is obtained. Alkali metals and alkaline earth metals have the ability to reduce the adsorption and poisoning of hydrocarbons in a rich atmosphere. When they are contained in the catalyst component-supporting layer, palladium and sintering are suppressed, and the low-temperature region and lack of oxygen The activity in the atmosphere can be further improved.

Further, the catalyst for purifying exhaust gas according to claim 8 is suitable for producing the alumina-based composite oxide according to any one of claims 1 to 7 by using a fine particle alumina hydrate colloid (hereinafter referred to as “alumina sol”). ), Zinc and a water-soluble salt of cerium and / or zirconium are dissolved or dispersed in water and stirred and mixed. At this time, a liquid in which each catalyst material is dissolved simultaneously or separately may be added. Next, after transferring the mixed solution to which the catalyst material was added to an autoclave,
Pressurized to 1-10 atm, heated from 50 ° C to 200 ° C,
Boil for 1 to 12 hours. After cooling, the mixed solution is obtained by removing water with a spray drier and then firing.

Further, the exhaust gas purifying catalyst according to the ninth aspect is useful for producing the alumina-based composite oxide according to any one of the first to seventh aspects, with boehmite alumina, zinc, cerium and / or zirconium. Is dissolved or dispersed in water and stirred and mixed. At this time, a liquid in which each catalyst material is dissolved simultaneously or separately may be added. Next, at least one member selected from the group consisting of formic acid, acetic acid, and succinic acid is gradually added to the mixture to adjust the pH to 3.0.
After adjusting so as to be in the range of 7.0 to 7.0, the pressure was increased to 1 to 10 atm by an autoclave, and the temperature was increased from 50 ° C to 200 ° C.
And boil for 1 to 12 hours. After cooling, the mixed solution is obtained by removing water with a spray drier and then firing.

The pH of the mixed solution of the catalyst raw materials is adjusted to 3.0 to 7.0.
By adjusting the range to 0, the boehmite alumina forms an organic salt complex and reacts with other additional elements to form a composite oxide. When the pH is lower than 3.0, boehmite alumina does not form an organic salt complex, and when the pH is higher than 7.0, a part of the boehmite alumina organic salt complex forms a hydroxide, May be difficult to react with other elements.

By using formic acid, acetic acid, succinic acid or the like for adjusting the pH, even if the precipitation cake is not sufficiently cleaned, no metal element remains. Can be decomposed and removed.

The obtained mixed solution is pressurized to 1 to 10 atm, heated to 50 to 200 ° C., and boiled for 1 to 12 hours. The reason for this is to peptize boehmite alumina having high crystallinity, to promote the formation of an organic salt complex, and to react this organic salt complex with other additional elements.

By producing such an alumina-based composite oxide, the BET specific surface area of the alumina-based composite oxide is increased, and the additive element is uniformly dispersed and dissolved in a crystal structure (spinel type structure). Can be.

The raw material of each element used in the exhaust gas purifying catalyst of the present invention can be produced by arbitrarily combining nitrate, carbonate, acetate, oxide and the like of each element.

Alumina-based composite oxides containing zinc, cerium and / or zirconium and aluminum used in the production of the exhaust gas purifying catalyst of the present invention include nitrates, carbonates, ammonium salts, acetates and the like of the above-mentioned elements. And any combination of alumina sol or boehmite alumina,
It is prepared by first preparing a mixed solution. It is particularly preferable to use a water-soluble salt and alumina sol or boehmite alumina from the viewpoint of improving the catalytic performance. Unlike aluminum nitrate, since alumina sol or boehmite alumina is used, exhaust gas and wastewater treatment for NO _x and ammonium nitrate derived from the raw material are significantly reduced when the precipitate is dried and calcined.

The removal of water can be appropriately selected from known methods such as an evaporation to dryness method and a spray drier method. In order to obtain the alumina-based composite oxide used in the present invention, the alumina-based composite oxide is not particularly limited, but forms an alumina-based composite oxide in which the added element is dissolved, and has a large specific surface area for supporting palladium with good dispersibility. In order to obtain, it is preferable to use a spray dryer. Furthermore, in order to form an alumina-based composite oxide in which the added element forms a solid solution and obtain a large specific surface area, the calcination may be performed, for example, at 600 ° C. to 900 ° C. in the air and / or under the flow of air. preferable.

The method of supporting palladium on the alumina-based composite oxide can be appropriately selected from known methods such as, for example, an impregnation method and a kneading method. preferable. As a raw material compound of palladium, any compound can be used as long as it is a water-soluble compound such as an ammonium salt, a chloride or a nitrate.

The heat treatment of the palladium-supported alumina-based composite oxide of the present invention is not particularly limited, but is performed after impregnation and drying, for example, at a temperature in the range of 400 ° C. to 700 ° C. in air and / or under an air stream. Is preferred.

Preferably, a catalyst for purifying exhaust gas according to claim 2 is obtained by adding cerium oxide powder to said alumina powder. The cerium oxide powder contains at least one selected from the group consisting of lanthanum, neodymium, and zirconium.

Further, the catalyst for purifying exhaust gas according to claim 4 is obtained by adding rhodium. As the raw material compound of rhodium, any compound can be used as long as it is water-soluble, such as nitrate, halide, acetate and the like.

The method of supporting rhodium on the alumina can be appropriately selected from, for example, an impregnation method and a kneading method, but it is particularly preferable to use the impregnation method. The subsequent removal of water can be appropriately selected from known methods such as an evaporation to dryness method. The heat treatment of the rhodium-supported alumina powder used in the present invention is not particularly limited.
It is preferable to carry out at a temperature in the range of 00 ° C. in air and / or under air flow.

Preferably, an exhaust gas purifying catalyst according to claim 5 is obtained by adding zirconium oxide powder to said rhodium-supported alumina powder. The zirconium oxide powder contains at least one selected from the group consisting of lanthanum, neodymium and cerium. When cerium oxide powder is added to the exhaust gas purifying catalyst according to the fourth aspect, the cerium oxide strongly holds rhodium in an oxidized state, and consequently the purification performance is reduced. In contrast, by adding such zirconium oxide powder, rhodium can be more effectively maintained in an oxidation state suitable for exhaust gas purification.

The removal of water can be appropriately selected from known methods such as an evaporation to dryness method and a spray drier method. In order to obtain the alumina-based composite oxide used in the present invention, although not particularly limited, a large specific surface area for forming an alumina-based composite oxide in which the added element forms a solid solution, and for supporting palladium with good dispersibility. In order to obtain, it is preferable to use a spray dryer. Furthermore, in order to form an alumina-based composite oxide in which the added element forms a solid solution and obtain a large specific surface area, the calcination may be performed, for example, at 600 ° C. to 900 ° C. in the air and / or under the flow of air. preferable.

The exhaust gas purifying catalyst according to the present invention thus obtained can be effectively used without a carrier. However, the catalyst can be pulverized / slurried, coated on a catalyst carrier, and heated at 400 to 900 ° C. It is preferable to use it after firing. The catalyst carrier can be appropriately selected from known catalyst carriers and used, and examples thereof include a monolith carrier made of a refractory material and a metal carrier.

The shape of the catalyst carrier is not particularly limited, but it is usually preferable to use it in a honeycomb shape, and the catalyst powder is applied to various honeycomb base materials.
As the honeycomb material, cordierite materials such as ceramics are generally used in general, but it is also possible to use many honeycomb materials made of a metal material such as ferrite stainless steel, and further, the catalyst powder itself is formed into a honeycomb shape. May be. 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, which 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 depends on the total amount of the catalyst components per liter of the catalyst.
50-400 g is preferred. The more catalyst components is preferable from the viewpoint of catalytic activity and catalyst life, when the coating layer becomes too thick, HC, CO, since the reaction gas such as NO _x becomes poor diffusion, these gases sufficiently catalyst Contact cannot be achieved, and the effect of increasing the amount of activity is saturated, and further, the gas passage resistance increases. Therefore, the coat layer amount is
The amount is preferably 50 g to 400 g per liter of the catalyst.

More preferably, the obtained exhaust gas purifying catalyst can be impregnated and supported 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,
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 include oxides, acetates, hydroxides, nitrates,
It is water-soluble such as carbonate. This makes it possible to carry the alkali metal and / or alkaline earth metal as a basic element in the vicinity of palladium with good dispersibility.
At this time, the starting compounds of the alkali metal and the alkaline earth metal may be contained simultaneously or separately.

That is, an aqueous solution of a powder comprising an alkali metal compound and / or an 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. ° C to 600
It is baked at ℃. This is because, once the alkali metal and alkaline earth metal raw material compounds are heat-treated at a low temperature and contained in the coat layer in the form of an oxide, it becomes difficult to form a composite oxide even when exposed to a high temperature later. If the calcination temperature is less than 200 ° C., the alkali metal compound and the alkaline earth metal compound cannot be sufficiently in the form of an oxide. No difference is obtained.

[0065]

The present invention will be described with reference to the following examples and comparative examples. Unless otherwise specified, “parts” means “parts by weight”.

Example 1 Fine particle alumina hydrate colloid (Al ₂ O ₃ as 20
Weight%), 875 g of zinc nitrate and 426 g of cerium acetate were dissolved in water, and then pressurized to 2 atm.
After heating at 50 ° C. for 5 hours, moisture was removed with a spray drier and dried, followed by baking at 750 ° C. for 2 hours.
Ce _0.1 Zn _0.3 Al _2.0 Ox powder was obtained. This Ce
_0.1 Zn _0.3 Al _2.0 O _x powder was impregnated with an aqueous solution of palladium nitrate, dried at 150 ° C. for 12 hours, and calcined at 400 ° C. for 1 hour to obtain Pd-supported alumina powder (powder A). The Pd concentration of this powder A was 1.27% by weight.

Cerium oxide powder (powder B) containing 1 mol% of lanthanum (2 wt% in terms of La ₂ O ₃ ) and 32 mol% of zirconium (25 wt% in terms of ZrO ₂ )
Is impregnated with an aqueous solution of palladium nitrate, dried at 150 ° C. for 12 hours, and calcined at 400 ° C. for 1 hour to obtain Pd-supported cerium oxide (La _0.01 Zr _0.32 Ce _0.67 Ox) powder C)
I got The Pd concentration of this powder C was 1.07% by weight.

970 g of powder A, 500 g of powder C, 30 g of activated alumina and 1500 g of nitric acid aqueous solution were charged into a magnetic ball mill, mixed and powdered to obtain a slurry. This slurry liquid is applied to a cordierite-based monolithic carrier (1.3).
L, 400 cells), and the excess slurry in the cells was removed by air flow, dried, and fired at 400 ° C. for 1 hour. This operation was performed twice, and the coat weight 150 g / L-
A cordierite monolithic carrier carrying a catalyst component as a carrier was obtained. The supported amount of palladium was 50 g / cf (1.77 g /
L).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier carrying the catalyst component.
It was calcined at 00 ° C. for 1 hour, and contained 10 g / L of BaO to obtain an exhaust gas purifying catalyst.

Example 2 Instead of Ce _0.1 Zn _0.3 Al _2.0 O _x powder, Zr _0.1
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that Zn _0.3 Al _2.0 O _x powder was used.

[0071]Example 3 Ce_0.1Zn_0.3Al_2.0O_xCe instead of powder_0.05
Zr_0.05Zn_0.3Al _2.0O_xExcept for using powder,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

[0072]Example 4 Ce_0.1Zn_0.3Al_2.0O_xCe instead of powder_0.05
Zr_0.05Zn_0.5Al _2.0O_xExcept for using powder,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

[0073]Example 5 Ce_0.1Zn_0.3Al_2.0O_xCe instead of powder_0.1
Zr_0.1Zn_0.3Al _2.0O_xExcept for using powder,
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

[0074]Example 6 Instead of powder A and powder C, 0.73% by weight of Pd
Ce supported_0.1Zn _0.3Al_2.0O_xPowder and powder B
Except that a powder carrying 2.12% by weight of Pd was used.
In the same manner as in Example 1, an exhaust gas purifying catalyst was obtained.

Example 7 Boehmite alumina (80% by weight as Al ₂ O ₃ ) 5
2,000 g, 875 g of zinc nitrate, 213 g of cerium nitrate, and 211 g of zirconium nitrate dissolved in water,
After adding 1000 g of 10% -acetic acid aqueous solution and adjusting the pH to about 4.0, pressurizing to 2 atm, heating at 150 ° C. for 5 hours, removing water by a spray drier, drying, and then heating at 750 ° C. Bake for 2 hours, Ce _0.05 Zr
_{A 0.05} Zn _0.3 Al _2.0 O _x powder was obtained. This Ce _0.05 Z
r _0.05 Zn _0.3 Al _2.0 O _x powder impregnated with an aqueous solution of palladium nitrate, dried at 150 ° C. for 12 hours, and then dried at 400 ° C.
For 1 hour to obtain Pd-supported alumina powder (powder D). The Pd concentration of this powder D was 1.12% by weight.

970 g of the powder D, 500 g of the powder C obtained in Example 1, 30 g of activated alumina, and 1 part of an aqueous nitric acid solution
500 g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), and excess slurry in the cells was removed by an air stream and dried, and then dried at 400 ° C.
For 1 hour. This operation was performed twice to obtain a catalyst component-carrying cordierite monolith carrier having a coat weight of 150 g / L-carrier. The supported amount of palladium is 45.8 g /
cf (1.62 g / L).

An alumina powder (powder E) containing 3 mol% of zirconium (6.3% by weight in terms of ZrO ₂ ) is impregnated with an aqueous rhodium nitrate solution, dried at 150 ° C. for 12 hours, and then at 400 ° C. for 1 hour. By baking, Rh-supported alumina powder (powder F) was obtained. The Rh concentration of this powder F was 0.74% by weight.

Powder F 200 g, La 1 mol% Ce 2
180 g of zirconium oxide powder (powder G) of 0 mol% Zr 79 mol%, activated alumina 20 g, aqueous nitric acid solution 10
00g was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry.

This slurry liquid was adhered to the above-mentioned cordierite-based monolith carrier having a catalyst component-supported layer in which a palladium-containing catalyst component layer was adhered to a cordierite-based monolith carrier (1.3 L, 400 cells), and the air in the cell was flown by air. Excess slurry was removed, dried and calcined at 400 ° C. for 1 hour.
This operation was performed once, and the coating amount of the rhodium-containing catalyst component layer was 40 g / L (the total coating amount was 190 g / L,
(50 g / L, surface layer: 40 g / L) -a catalyst was obtained. The amount of rhodium supported was 4.2 g / cf (0.15 g / L).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier carrying the catalyst component.
It was calcined at 400 ° C. for 1 hour, and contained 10 g / L of BaO to obtain an exhaust gas purifying catalyst.

Example 8 500 g of powder C obtained in Example 1, powder D, powder F and powder G obtained in Example 7, and activated alumina 50 g
g and 2500 g of a nitric acid aqueous solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried, and calcined at 400 ° C. for 1 hour. This operation was performed twice to obtain a cordierite-type monolithic carrier carrying a catalyst component having a coat weight of 190 g / L-carrier. The supported amount of palladium was 45.8 g / cf (1.62 g / L), and the supported amount of rhodium was 4.2 g / cf (0.15 g / L).

Next, a barium acetate solution was adhered to the cordierite monolithic carrier supporting the catalyst component.
It was calcined at 00 degrees for 1 hour, and contained 10 g / L of BaO to obtain an exhaust gas purifying catalyst.

Comparative Example 1 Instead of Ce _0.1 Zn _0.3 Al _2.0 O _x , Zn _0.3 Al
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _2.0 O _x was used.

[0084] Alternatively Ce _0.1 Zn Comparative Example _{2 Ce 0.1 Zn 0.3 Al 2.0 O} x
Except for using ₁ Al _2.0 O _x ,
An exhaust gas purifying catalyst was obtained.

Comparative Example 3 Ce _0.1 Zn _0.3 Al _2.0 O obtained in the same manner as in Example 1.
_x was impregnated with an aqueous solution of palladium nitrate, dried at 150 ° C. for 12 hours, and calcined at 400 ° C. for 1 hour to obtain powder H having a Pd concentration of 0.18% by weight. Powder B was impregnated with an aqueous solution of palladium nitrate and dried at 150 ° C. for 12 hours.
Baking at 00 ° C. for 1 hour to obtain Pd-supported cerium oxide (L
a _0.01 Zr _0.32 Ce _0.67 O _x ) powder (powder I) was obtained.
The Pd concentration of this powder I was 3.18% by weight.

[0086] 970 g of the powder H, 500 g of powder I, 30 g of activated alumina and 1500 g of an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid is applied to a cordierite-based monolithic carrier (1.3 L,
(400 cells), the excess slurry in the cells was removed by an air stream, dried, and fired at 400 ° C. for 1 hour. This operation was performed twice to obtain a catalyst component-carrying cordierite monolith carrier having a coat weight of 150 g / L-carrier. The supported amount of palladium was 50 g / cf (1.77 g / L).

Then, a barium acetate solution was adhered to the cordierite monolithic carrier carrying the catalyst component.
The mixture was calcined at 00 ° C. for 1 hour to obtain an exhaust gas purifying catalyst containing 10 g / L of BaO.

Comparative Example 4 200 g of powder F and G180 obtained in Example 7
g, activated alumina 20 g and nitric acid aqueous solution 1000 g were put into a magnetic ball mill, mixed and pulverized to obtain a slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried, and calcined at 400 ° C. for 1 hour. This operation was performed once to obtain a cordierite-based monolithic carrier a carrying a catalyst component having a coating weight of 40 g / L-rhodium-containing catalyst component layer. The amount of rhodium supported was 4.2 g / cf (0.15 g / L).

970 g of the powder D obtained in Example 7, 500 g of the powder C obtained in Example 1, 30 g of activated alumina, and 1500 g of an aqueous nitric acid solution were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry. The slurry liquid is adhered to the catalyst component-carrying cordierite monolithic carrier a in which a rhodium-containing catalyst component layer is adhered to a cordierite monolithic carrier (1.3 L, 400 cells), and excess air in the cells is flowed by air. The slurry is removed and dried.
Fired for hours. This operation was performed twice, and the coat weight 15
0 g / L (total coating weight 190 g / L, total 40 g / L
L, surface layer 150 g / L)-a cordierite monolithic carrier b carrying a catalyst component as a carrier was obtained. Palladium loading is 4
It was 5.8 g / cf (1.62 g / L).

Next, a barium acetate solution was adhered to the catalyst component-carrying cordierite monolithic carrier b,
It was calcined at 400 ° C. for 1 hour to obtain an exhaust gas purifying catalyst containing 10 g / L of BaO.

Comparative Example 5 Instead of Ce _0.1 Zn _0.3 Al _2.0 O _x in Example 1, an aqueous solution in which 875 g of zinc nitrate and 426 g of cerium nitrate were dissolved in 1000 g of pure water was used to prepare an alumina powder 100
0 g, dried at 150 ° C. for 12 hours,
Ce _0.1 Zn _0.3 Al _2.0 obtained by baking at 00 ° C. for 2 hours
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that _Ox powder (powder J) was used.

The compositions of the exhaust gas purifying catalysts of Examples 1 to 8 and Comparative Examples 1 to 5 are shown in Table 1.

[0093]

[Table 1]

Test Examples The exhaust gas purifying catalysts of Examples 1 to 8 and Comparative Examples 1 to 5 were durable under the following durability conditions, and then were evaluated for catalytic activity under the following evaluation conditions.

Endurance conditions Engine displacement 4400cc Fuel unleaded gasoline Catalyst inlet gas temperature 700 ° C Endurance time 100 hours Inlet gas composition CO 0.5 ± 0.1% O ₂ 0.5 ± 0.1% HC About 1100ppm NO 1300ppm CO ₂ 15% A / F fluctuation 5500 times (cycle 65 seconds / time) Cycle: A / F = 14.655 seconds Fuel cut 5 seconds Rich spike 5 seconds

Evaluation condition 1: Low-temperature active engine displacement : 2000 cc fuel Unleaded gasoline Heating rate: 10 ° C./min Measurement temperature range: 150 to 500 ° C. The low-temperature activity of each exhaust gas purifying catalyst after endurance was measured by HC, C
O and NO _x temperature when the conversion reached 50% (T5
0 / ° C.), and the results are shown in Table 2.

Evaluation condition 2: Purification performance Engine displacement 2000 cc Fuel Unleaded gasoline Catalyst inlet exhaust gas temperature 500 ° C. The purifying performance of the exhaust gas purifying catalyst after the durability test was determined HC, the average conversion rate (%) The following equation for CO and NO _x at stoichiometric atmosphere, and the results are shown in Table 3.

[0098]

(Equation 4)

(Equation 5)

(Equation 6)

[0099]

[Table 2]

[0100]

The exhaust gas purifying catalyst according to claim 1 is
It is excellent in durability and purification performance, and can improve exhaust gas purification performance such as low-temperature activity and stoichiometric conversion after durability.

The exhaust gas purifying catalyst according to claim 2 further suppresses the inactivation of palladium, in addition to the above effects,
The catalyst performance after durability can be improved.

The exhaust gas purifying catalyst according to the third aspect, in addition to the above-mentioned effects, can enhance the dispersibility of palladium and improve the low-temperature activity from the initial stage to the endurance.

The exhaust gas purifying catalyst according to claim 4 can further improve the purifying performance in a rich region in addition to the above effects.

In the exhaust gas purifying catalyst according to the fifth aspect, in addition to the above-described effects, deterioration due to reduction of rhodium in the catalyst component can be suppressed, and the low-temperature activity and the purifying performance can be further improved.

The exhaust gas purifying catalyst according to claim 6 can further improve low-temperature activity and purifying performance by combining palladium and rhodium in addition to the above effects.

The exhaust gas purifying catalyst according to claim 7, in addition to the above-mentioned effects, reduces the HC adsorption poisoning action in a rich atmosphere and suppresses the sintering of palladium.
It is possible to improve the low-temperature activity and the NO _x purification ability in a reducing atmosphere.

According to the exhaust gas purifying catalysts of the eighth and ninth aspects, the exhaust gas purifying catalyst of the present invention can be efficiently produced, and in particular, an alumina-based composite oxide in which the added element is dissolved in solid form can be formed. Further, an exhaust gas purifying catalyst having a large specific surface area for supporting palladium with good dispersibility can be obtained.

Claims (9)

[Claims] 1. A monolithic catalyst having a catalyst component-supporting layer, comprising at least palladium as a catalyst component and a metal aluminate powder, wherein the metal aluminate powder has the following general formula: _d Zn _a Al _b O _c (where Y is cerium and / or zirconium, a, b, c and d represent the atomic ratio of each element, and b
= 2.0, a = 0.1-0.6, d = 0.01-
0.3, c is the number of oxygen atoms required to satisfy the valence of each of the above-mentioned components). 2. The exhaust gas purifying catalyst according to claim 1,
A catalyst for purifying exhaust gas, further comprising a cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium in terms of metal at 1 to 40 mol% and cerium at 60 to 98 mol%. . 3. The exhaust gas purifying catalyst according to claim 1, wherein the total palladium amount is 30 to 8 in terms of metal.
An exhaust gas purifying catalyst, wherein 0% by weight of palladium is contained in an alumina-based composite oxide. 4. An exhaust gas purifying catalyst according to claim 1, wherein the exhaust gas purifying catalyst further comprises rhodium. 5. The exhaust gas purifying catalyst according to claim 4,
Further, at least one selected from the group consisting of lanthanum, neodymium and cerium is 1 to 40 mol% in terms of metal,
An exhaust gas purifying catalyst comprising a zirconium oxide containing 60 to 98 mol% of zirconium. 6. The exhaust gas purifying catalyst according to claim 4, wherein the rhodium-containing layer is arranged on the same layer as palladium and / or above the palladium-containing layer. 7. The exhaust gas purifying catalyst according to claim 1, further comprising at least one selected from the group consisting of alkali metals and alkaline earth metals. Gas purification catalyst. 8. In producing the alumina-based composite oxide according to claim 1, a water-soluble salt of fine-particle alumina hydrate, zinc, and cerium and / or zirconium is dissolved in water. Or after dispersing, 1-10
A method for producing an exhaust gas purifying catalyst, characterized in that the catalyst is heated to 50 to 200 ° C. under pressure, dried, dried and calcined. 9. In producing the alumina-based composite oxide according to any one of claims 1 to 7, boehmite alumina, zinc, and a water-soluble salt of cerium and / or zirconium are dissolved or dispersed in water. At least one aqueous solution selected from the group consisting of formic acid, acetic acid, and succinic acid is added to the mixture, and the pH is adjusted to be in the range of 3.0 to 7.0, and the pressure is increased to 1 to 10 atm. A method for producing an exhaust gas purifying catalyst, comprising heating to 50 to 200 ° C., drying after removing moisture, and then calcining.