JPH09248462A - Exhaust gas-purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas-purifying catalyst enhanced in durability and having excellent low temp. activity and purifying capacity even after high temp. endurance. SOLUTION: This monolithic structure type catalyst has a catalyst component support layer. As a catalyst component, rhodium and hexaaluminate are contained. This hexaaluminate contains nickel, cobalt, iron, manganese, chromium, potassium, strontium, barium or lanthanum or an arbitrary mixture of these elements. Palladium, platinum, zirconium oxide, cerium oxide, an alkali metal or an alkaline earth metal may be added.

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 purification catalyst that can efficiently purify (NO _x )) and that is excellent in low temperature activity and purification performance even after high temperature durability.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas purifying catalyst is not sufficiently durable at high temperatures, and the catalyst deteriorates and its purifying performance remarkably deteriorates. Therefore, exhaust gas purifying is excellent in low temperature activity and purifying performance even after high temperature durability. The development of catalysts for automobiles is expected.

As such exhaust gas purifying catalysts, for example, JP-B-58-20307 and JP-A-62-28
2641, JP-A-4-284847, JP-A-6-378, and JP-A-7-60118. The exhaust gas purifying catalyst described in Japanese Patent Publication No. 58-20307 is a catalyst in which a composition comprising platinum, rhodium and cerium is supported on a refractory carrier, and specifically, platinum on alumina or cerium oxide. , Palladium, rhodium, and other platinum group elements, and a monolithic carrier coated with the element.

Further, JP-A-62-282641 discloses an exhaust gas purifying catalyst in which rhodium is supported on zirconium oxide, and specifically, zirconium oxide containing rhodium, activated alumina, A slurry containing cerium oxide and alumina sol is adhered to a carrier, dried and fired, and then platinum is supported.

Japanese Unexamined Patent Publication (Kokai) No. 4-284847 discloses platinum, rhodium, activated alumina, cerium oxide, etc. which have been conventionally used as catalyst components, as well as cerium oxide and lanthanum, praseodymium, yttrium, neodymium, 2A group. And a zirconium compound stabilized by one or more metal oxides selected from Group 3B.

Japanese Unexamined Patent Publication (Kokai) No. 6-378 discloses that activated alumina and cerium oxide are mixed with at least one of platinum and palladium as a catalyst component and potassium as a basic element.
An exhaust gas purifying catalyst carrying an oxide of at least one metal selected from the group consisting of cesium, strontium and barium has been proposed. In other words, the catalyst is a platinum group element, activated alumina, cerium oxide, etc.
In addition to those which have been conventionally used as a catalyst component, at least one kind of a basic element, which is a potassium compound, a cesium compound, a strontium compound and a barium compound, is combined.

Japanese Unexamined Patent Publication (Kokai) 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 having a surface area of 30 to 300 m ² / g. There has been proposed a noble metal catalyst using the oxygen-ion conductive composite having the rhodium / platinum and rhodium / palladium as a supporting substrate.

[0008]

However, in the conventional catalyst described in the above publication, it is necessary to use a large amount of noble metal in order to maintain high performance from the initial stage to the end stage. Therefore, as a three-way catalyst for purifying exhaust gas, a catalyst that can obtain high performance even if the amount of precious metal used is small is desired. However, when the amount of the noble metal is reduced, there is a problem that the durability under high temperature is insufficient and the catalytic activity and the purification performance in the low temperature region deteriorate after the high temperature durability.

This is based on the stoichiometric air-fuel ratio (hereinafter referred to as "stoichiometric").
The exhaust gas of automobiles whose composition varies widely from a reducing atmosphere with insufficient oxygen concentration (hereinafter referred to as "rich") to an oxidizing atmosphere with excessive oxygen concentration (hereinafter referred to as "lean"). It is considered that deterioration (sintering) of the noble metal species is promoted in the atmosphere, and as a result, the purification performance deteriorates. In particular, when the amount of noble metal is reduced, the above-mentioned influence becomes remarkable, and there is a problem that the purification performance further deteriorates.

Further, alumina has insufficient thermal stability, and its crystal structure changes at high temperature to cause a phase transition to α-alumina having a remarkably small BET specific surface area. At this time, it is considered that the sintering of the noble metal is promoted, and that the alumina undergoes a solid-phase reaction with the noble metal to form an inactive compound, and as a result, the purification performance is greatly reduced. On the other hand, hexaaluminate has excellent structural stability, but B
Since the ET specific surface area is small, the dispersibility of noble metal species is poor, and there is a drawback that it is difficult to obtain sufficient low-temperature activity and purification performance from the initial stage to the end stage.

The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is to improve durability and to provide excellent low-temperature activity and purification performance even after high-temperature durability. An object of the present invention is to provide a catalyst for purifying the exhaust gas.

[0012]

Means for Solving the Problems As a result of earnest research for solving the above problems, the present inventor has found that by incorporating hexaaluminate containing a specific element together with rhodium into a catalyst component-supporting layer, rhodium The inventors have found that the high temperature durability and the catalytic activity can be improved, and the low temperature activity and the purification performance after the high temperature durability are remarkably improved and maintained, and the present invention has been accomplished.

That is, the exhaust gas purifying catalyst according to claim 1 is a monolithic structure type catalyst comprising a monolithic structure type carrier provided with a catalyst component supporting layer, which contains at least rhodium and hexaaluminate as a catalyst component. It is characterized in that the aluminate contains at least one selected from the group consisting of nickel, cobalt, iron, manganese, chromium, potassium, strontium, barium and lanthanum.

In the catalyst of claim 2, the hexaaluminate has the following general formula [X] _a [Y] _b Al _{12 -b} O _c (wherein X is potassium, strontium, barium and At least one element selected from the group consisting of lanthanum, Y is at least one element selected from the group consisting of nickel, cobalt, iron, manganese and chromium, and a, b and c are Represents the atomic ratio of each element, a
= 1.0, b = 0 to 1.0, and c is the number of oxygen atoms required to satisfy the valence of each component), and the high temperature of the catalyst according to claim 1. It is one that has improved structural stability below.

The catalyst according to claim 3 is one in which 1 to 70% by weight of metal of the total rhodium is converted to rhodium on the hexaaluminate. The catalyst according to claim 1 or 2 It has improved low temperature activity and catalyst activity at the initial stage and after durability. Further, in the catalyst according to claim 4, one kind selected from the group consisting of cerium, neodymium and lanthanum as an oxygen storage material is 1 to 1 in terms of metal.
4. A zirconium oxide containing 40 mol% and 60 to 98 mol% of zirconium is contained.
It is a catalyst in which the catalyst activity of any of the catalysts in a rich atmosphere is further improved.

Further, the catalyst according to claim 4 or 5 is a catalyst further containing palladium and / or platinum, or in addition to this, at least one metal selected from the group consisting of cerium, zirconium and lanthanum. 1-10 in conversion
Alumina containing mol% and activated alumina, and 1 to 40 mol% of at least one selected from the group consisting of zirconium, neodymium and lanthanum in terms of metal, and cerium oxide containing 60 to 98 mol% of cerium. It is the contained catalyst. These catalysts have improved low-temperature activity, catalytic activity under rich and stoichiometric atmospheres, and improved durability against poisonous substances such as lead (hereinafter referred to as "poisoning resistance"). Furthermore, the catalyst according to claim 7 further contains an alkali metal and / or an alkaline earth metal, and the catalyst activity according to any one of claims 1 to 6 is improved in a rich atmosphere. It is a thing.

[0017]

In the exhaust gas purifying catalyst of the present invention, rhodium is supported on the hexaaluminate powder containing the specific element, so that the sintering of rhodium at high temperature can be suppressed. Further, in the present invention, by adjusting the hexaaluminate to a specific composition ratio, it is possible to form a hexaaluminate structure in the added element and prevent the oxide of the added element from existing. Therefore, it is possible to avoid formation of an inactive compound of rhodium and the oxide of the additional element, and it is possible to obtain a hexaaluminate powder having improved structural stability at high temperatures.

Further, in the total rhodium amount, 1 to 1 in terms of metal
By supporting 70% by weight of rhodium on the hexaaluminate, it is possible to improve the purification performance after high temperature durability. Further, by using the rhodium-supported alumina powder in combination, the initial performance of the catalyst can be improved and the coating property of the hexaaluminate can be improved.

In the present invention, it is also possible to contain a zirconium oxide powder containing at least one selected from the group consisting of cerium, neodymium and lanthanum, whereby a zirconium oxide having a high oxygen storage capacity is contained. Since the substance releases lattice oxygen and adsorbed oxygen in a rich atmosphere and in the vicinity of stoichiometry, and makes the oxidation state of rhodium suitable for purification of exhaust gas, it is possible to suppress deterioration of rhodium catalytic ability.

Further, at least one of palladium and platinum may be contained, whereby the synergistic action of rhodium with palladium and platinum may improve the low temperature activity after high temperature endurance, the purification performance and the poisoning resistance. It can also be improved. In this case, the catalyst component-supporting layer further contains a cerium oxide containing 1 to 40 mol% and 60 to 98 mol% of cerium in terms of metal of one selected from the group consisting of zirconium, neodymium and lanthanum. It is also possible to make the cerium oxide, which has a high oxygen storage capacity, release lattice oxygen and adsorbed oxygen in a rich atmosphere and near stoichiometry, and make the oxidation state of palladium and platinum suitable for purification of exhaust gas. Therefore, it is possible to suppress the decrease in catalytic ability.

Furthermore, it is also possible to contain at least one selected from the group consisting of alkali metals and alkaline earth metals, whereby the purification performance improving effect can be obtained. That is, when these are contained in the catalyst component supporting layer, the HC adsorption poisoning effect in a rich atmosphere is mitigated and the sintering of palladium is suppressed, so that the activity at a low temperature and the activity in a reducing atmosphere are further improved. be able to.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the exhaust gas purifying catalyst of the present invention will be described in detail. The exhaust gas purifying catalyst of the present invention is an integral structure type catalyst having a catalyst component supporting layer, and contains rhodium and hexaaluminate containing a specific element as a catalyst component. As described above, in the catalyst of the present invention, the catalyst component-supporting layer contains at least rhodium as a noble metal, and the content of the rhodium is preferably 0.01 to 3 g per 1 l of the catalyst. If it is less than 0.01 g, low-temperature activity and purification performance are not sufficiently expressed, and if it exceeds 3 g, the catalytic activity of rhodium is saturated, which is not economically effective, which is not preferable.

As mentioned above, the reason why hexaaluminate is used is that it can improve the high temperature durability of rhodium and is suitable as a base material carrying rhodium. Furthermore, the inclusion of at least one selected from the group consisting of nickel, cobalt, iron, manganese, chromium, potassium, strontium, barium and lanthanum in the hexaaluminate maintains / improves the purification performance after endurance. This is to allow it. The amount of such hexaaluminate used is preferably 5 to 100 g per liter of the catalyst. If it is less than 5 g, sufficient durability of the precious metal cannot be obtained, and if it is used more than 100 g, the improving effect is saturated and it is not effective.

The above hexaaluminate is represented by the following general formula [X] _a [Y] _b Al _{12 -b} O _c (wherein X is selected from the group consisting of potassium, strontium, barium and lanthanum). Y is at least one element selected from the group consisting of nickel, cobalt, iron, manganese, and chromium, and a, b, and c are atomic ratios of the respective elements. Represents a
= 1.0, b = 0 to 1.0, and c is the number of oxygen atoms required to satisfy the valences of the above components).

In the above general formula, when a is less than 1.0, an element selected from the group consisting of potassium, strontium, barium and lanthanum cannot form a stable hexaaluminate structure, and sufficient thermal stability is obtained. It is not preferable because it may not be possible. On the other hand, when a = 1.0 is exceeded, the added element cannot be completely dissolved in the crystal structure of hexaaluminate and is ubiquitous as an oxide, and conversely the high temperature durability may be deteriorated. In addition, in order to improve the thermal stability and cocatalyst action of hexaaluminate, nickel, cobalt,
An element selected from the group consisting of iron, manganese and chromium can be optionally added. However, when b exceeds 1.0, the added element cannot be dissolved in the crystal structure of hexaaluminate and is ubiquitous as an oxide, and on the contrary, the performance after high temperature durability is deteriorated, which is not preferable.

Further, in the catalyst of the present invention, it is preferable that 1 to 70 wt% of the total rhodium amount in terms of metal is supported on hexaaluminate. When the amount of rhodium supported on hexaaluminate is less than 1% by weight, sufficient durability and improvement effect cannot be obtained, and when it exceeds 70% by weight, the improvement effect may be saturated or the coating property may be deteriorated. Not preferable.

Further, in the catalyst of the present invention, zirconium oxide containing cerium or the like can be contained in addition to the above catalyst components. As the zirconium oxide, at least one element selected from the group consisting of cerium, neodymium, and lanthanum is 1 to 40 in terms of metal.
Those containing mol% and zirconium in an amount of 60 to 98 mol% are preferable. The content of 1 to 40 mol% means that at least one element selected from the group consisting of cerium, neodymium and lanthanum is added to zirconium oxide (particularly ZrO ₂ ), and the oxygen releasing ability and BET ratio of ZrO ₂ are increased. This is because the surface area and thermal stability are remarkably improved. If it is less than 1 mol%, there is no change from the case of only ZrO ₂ , and the effect of adding the above-mentioned elements does not appear, and if it exceeds 40 mol%, this effect is saturated or, conversely, deteriorated, which is not preferable.

The catalyst of the present invention may contain palladium and / or platinum in addition to the above catalyst components. In this case, the content of palladium and / or platinum is preferably 0.1 to 10 g in 1 l of the catalyst. If it is less than 0.1 g, low-temperature activity and purification performance are not sufficiently exhibited, and conversely, if it exceeds 10 g, the catalytic activity of platinum or palladium is saturated, which is not economically effective, which is not preferable.

Alumina is suitable for the above-mentioned base material carrying palladium and / or platinum in order to enhance the dispersibility of palladium and platinum and improve the catalytic performance. Especially,
In order to enhance the structural stability of alumina after high-temperature durability and to suppress the phase transition to α-alumina and the decrease in BET specific surface area, the above-mentioned alumina contains at least one selected from the group consisting of cerium, zirconium and lanthanum. It is preferable that the seed is contained in an amount of 1 to 10 mol% in terms of metal. The amount of the alumina used is preferably 10 to 200 g per liter of the catalyst, and if it is less than 10 g, sufficient dispersibility of the noble metal cannot be obtained, and even if it is used in excess of 200 g, the catalyst performance is saturated, which is a remarkable improvement. The effect may not be obtained.

Furthermore, the catalyst of the present invention may contain cerium oxide in addition to the above catalyst components. As the cerium oxide, one containing 1 to 40 mol% and 60 to 98 mol% of cerium in terms of metal of one selected from the group consisting of zirconium, neodymium and lanthanum is preferable. 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 (particularly CeO ₂ ), and the oxygen releasing capacity and BET ratio of CeO ₂ are increased. This is because the surface area and thermal stability are remarkably improved. If it is less than 1 mol%, it is not different from the case of CeO ₂ alone, and the effect of adding the above-mentioned elements does not appear, and if it exceeds 40 mol%, this effect may be saturated or conversely deteriorated, which is not preferable.

The catalyst of the present invention may contain an alkali metal and / or an alkaline earth metal in addition to the above catalyst components. Alkali metals and alkaline earth metals that can be used include lithium, sodium, potassium, cesium, magnesium, calcium, strontium or barium and any combination thereof.
The content is preferably 1 to 40 g in 1 liter of the catalyst. 1
If it is less than g, adsorption poisoning of hydrocarbons and sintering of palladium cannot be suppressed, and if it exceeds 40 g, a significant amount increasing effect cannot be obtained and conversely the performance may be deteriorated.

Next, a method of manufacturing the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purifying catalyst of the present invention is a hexaaluminate containing at least one component selected from the group consisting of nickel, cobalt, iron, manganese, chromium, potassium, strontium, barium and lanthanum, and an aluminum component, It can be produced by impregnating and supporting rhodium and further heat-treating it. Here, the hexaaluminate containing aluminum and at least one component selected from the group consisting of nickel, cobalt, iron, manganese, chromium, potassium, strontium, barium and lanthanum used is a nitrate of each of these elements. , Carbonates, acetates, oxides and the like can be arbitrarily combined to produce.

The first heat treatment performed to obtain hexaaluminate is not particularly limited, but the added element and aluminum form a hexaaluminate structure, and the rhodium is stabilized at a high temperature. In order to achieve the above, it is preferable to carry out the firing at a relatively high temperature of 600 to 1300 ° C. in the air and / or under the air flow. The method for supporting rhodium on hexaaluminate can be appropriately selected from known methods such as an impregnation method and a kneading method, and the impregnation method is particularly preferable. Any raw material compound of rhodium may be used as long as it is water-soluble, such as nitrate.

By the way, in the exhaust gas purifying catalyst of the present invention obtained as described above, the uniform crystal structure of hexaaluminate excellent in thermal stability plays an important role in stabilizing rhodium at high temperature. Plays. On the other hand, in the catalyst obtained without using the hexaaluminate represented by the above general formula, the added element does not form a hexaaluminate structure, and the surplus additional element is ubiquitously present as an oxide on the surface. , The catalytic activity of rhodium and the purification performance after endurance may decrease.

In producing the catalyst of the present invention, the hexaaluminate powder carrying rhodium and the alumina powder carrying rhodium can be used in combination. As described above, by adding the rhodium-supported alumina powder, it is possible to ensure the maintenance of high purification performance from the initial stage to the end of durability and the improvement of the coating property of the hexaaluminate powder.

Further, a zirconium oxide containing at least one selected from the group consisting of cerium, neodymium and lanthanum can be added. By adding zirconium oxide powder containing these cerium and the like, the oxidation state of rhodium in a reducing atmosphere,
The state suitable for exhaust gas purification can be more effectively maintained. In addition to the above-mentioned catalyst component, it is also possible to add a powder in which palladium or platinum is carried by an impregnation method on alumina powder or cerium oxide powder. In this case, as the raw material compound of palladium or platinum, any compound can be used as long as it is water-soluble such as dinitrodiammine acid salt, chloride and nitrate.

Furthermore, it is possible to produce a catalyst by adding a predetermined cerium oxide powder to a powder obtained by impregnating alumina powder or cerium oxide powder with palladium or platinum by an impregnation method. Here, the predetermined cerium oxide powder contains at least one selected from the group consisting of zirconium, neodymium, and lanthanum. By adding such cerium oxide, palladium or platinum can be added in a reducing atmosphere. The oxidation state of can be more effectively maintained in a state suitable for purification of exhaust gas.

The catalyst for purifying exhaust gas of the present invention obtained as described above can be effectively used without a carrier, but various catalyst components are pulverized and slurried and coated on the catalyst carrier, It is preferable to use it after firing at 400 to 900 ° C. 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.

An integral structure type catalyst using a catalyst carrier is prepared by, for example, adding the noble metal-supporting hexaaluminate powder, the zirconium oxide powder, the noble metal-supporting alumina and the noble metal-supporting cerium oxide powder to the alumina sol. In addition, it can be manufactured by pulverizing in a wet process to form a slurry, adhering the obtained slurry to a catalyst carrier, and firing at a temperature in the range of 400 to 650 ° C. in air and / or under air flow. it can. At this time, in order to efficiently develop the synergistic effect of rhodium and palladium and platinum, the catalyst component layer containing palladium is arranged below the coat layer (inner layer side), and rhodium and platinum are the same catalyst component. It is preferably arranged on the upper side (surface layer side) of the coat layer contained in the layer.

The shape of the above-mentioned catalyst carrier is not particularly limited, but it is usually preferable to use a honeycomb-shaped one, and a catalyst-component powder is applied to various honeycomb-shaped base materials for use. As this honeycomb material, generally a cordierite material such as ceramic is often used, but it is also possible to use a honeycomb material made of a metal material such as ferritic stainless steel, and further, the catalyst component powder itself is formed into a honeycomb shape. You may 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 coating layer adhered to the honeycomb material is preferably 50 to 400 g per liter of the catalyst in total of the catalyst components. The larger the amount of the catalyst component-supporting layer, the more preferable from the viewpoint of catalytic activity and catalyst life, but if the coat layer becomes too thick, the reaction gas inside the catalyst-supporting layer becomes poor in diffusion and cannot sufficiently contact the catalyst, The effect of increasing the amount of activity saturates, and the gas passage resistance also increases. Therefore, the amount of the coat layer is preferably 50 to 400 g per liter of the catalyst.

Further, the monolithic structure type catalyst obtained as described above is impregnated and supported with an alkali metal and / or an alkaline earth metal to suppress adsorption poisoning of hydrocarbons and sintering of palladium. it can. Examples of alkali metals and alkaline earth metals that can be used include lithium, sodium, potassium, cesium, magnesium, calcium, strontium or barium, and any combination of these elements.

Examples of the use form of the above-mentioned alkali metal and alkaline earth metal include these various compounds, but water-soluble ones such as oxides, acetates and hydroxides are preferable. This makes it possible to support the alkaline metal and / or alkaline earth metal, which is a basic element, in the vicinity of palladium with good dispersibility. 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 carrier carrying a washcoat component and dried, and then in air and / or under air flow at 200 to 600 ° C. It may be fired at a relatively low temperature. If the baking temperature is less than 200 ° C, the alkali metal and / or alkaline earth metal compound cannot be in a sufficient oxide form, and conversely, even if it exceeds 600 ° C, the effect of the baking temperature is saturated, No significant difference is obtained.

[0044]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. (Example 1) 3 mol% of cerium (8.7 wt% in terms of CeO ₂ ), 3 mol% zirconium (6.3 wt% in terms of ZrO ₂ ) and 2 mol% of lanthanum (La ₂ O _3). Alumina (Ce _0.3 Zr) containing 5.5% by weight
_0.3 La _0.2 Al _0.92 O _x ) powder (powder A) was impregnated with an aqueous palladium nitrate solution and dried at 150 ° C. for 12 hours.
The Pd-supported alumina powder (powder B) was obtained by firing at 400 ° C. for 1 hour. The Pd concentration of this powder B was 1.7% by weight. 1 mol% of lanthanum (2 wt% in terms of La ₂ O ₃ ) and 32 mol% zirconium ( ₂ in terms of ZrO ₂ )
Cerium oxide powder (powder C) containing 5% by weight) was impregnated with an aqueous palladium nitrate solution, dried at 150 ° C. for 12 hours, and then baked at 400 ° C. for 1 hour to obtain a Pd-supporting cerium oxide powder (La _0.01 Zr). _0.32 Ce _0.67 O _X) to obtain a powder (powder D). The Pd concentration of this powder D was 0.75% by weight.

The powder B (468 g), the powder D (320 g), the activated alumina (12 g) and a nitric acid aqueous solution (100 g) were put into a magnetic ball mill, and mixed and pulverized to obtain a slurry. This slurry liquid was used as a cordierite monolith carrier (1.7 l,
(400 cells), excess slurry in the cells was removed by an air flow, dried, and fired at 400 ° C. for 1 hour. This operation was performed twice to obtain a catalyst having a coat layer weight of 182 g / l-support. The amount of palladium carried was 66.7 g / cf (2.
35 g / l).

Sr _1.0 Al ₁₂ O _x powder (powder E) was impregnated with an aqueous rhodium nitrate solution, dried at 150 ° C. for 12 hours, and then calcined at 400 ° C. for 1 hour to obtain Rh-supported Sr _1.0 Al.
₁₂ O _X powder (powder F) was obtained. The Rh concentration of this powder F was 1.06% by weight. Alumina (powder G) containing 3% by weight of Zr was impregnated with an aqueous rhodium nitrate solution, dried at 150 ° C. for 12 hours, and then calcined at 400 ° C. for 1 hour to obtain Rh.
An alumina powder (powder H) containing 3% by weight of supported Zr was obtained.
The Rh concentration of this powder H was 1.06% by weight. Powder A is impregnated with an aqueous platinum dinitrodiammnate solution,
After drying at ℃ for 12 hours, baking at 400 ℃ for 1 hour,
Pt-supported alumina powder (powder I) was obtained. The Pt concentration of this powder I was 1.1% by weight.

104 g of the powder F, 104 g of the powder H, and 198 g of the powder I, 1 mol% of lanthanum (1.2 wt% in terms of La ₂ O ₃ ) and 20 mol% cerium (25.8 wt% in terms of CeO ₂ ). 235 g of zirconium oxide powder (powder J) containing) was charged into a magnetic ball mill, 9.3 g of activated alumina and 1000 g of a nitrate aqueous solution were charged, and mixed and pulverized to obtain a slurry. This slurry liquid was attached to a cordierite-based monolithic carrier (1.7 l, 400 cells) carrying the above Pd-containing catalyst component layer, excess slurry in the cells was removed and dried by air flow, and the temperature was adjusted to 1 at 400 ° C. Burned for hours. A catalyst having a coat layer weight of 70 g / l-support was obtained. Rh loading amount is 6.7g / cf (0.24g / l)
Met. Then, a barium acetate solution was attached to the above-mentioned catalyst component-supporting cordierite monolithic carrier, and then 40
It was calcined at 0 ° C. for 1 hour and contained 20 g / l as BaO.

Example 2 Example 1 was repeated except that Ba _1.0 Al ₁₂ O _x powder was used instead of Sr _1.0 Al ₁₂ O _x powder.
An exhaust gas purifying catalyst was obtained in the same manner as described above. (Example 3) Instead of Sr _1.0 Al ₁₂ O _x powder, Sr _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _0.8 La _0.2 Al ₁₂ O _x powder was used. (Example 4) Instead of Sr _1.0 Al ₁₂ O _x powder, Ba
An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that _0.8 K _0.2 Al ₁₂ O _x powder was used.

Example 5 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that Sr _0.8 La _0.2 Mn _1.0 Al ₁₁ O _x powder was used instead of Sr _1.0 Al ₁₂ O _x powder. It was (Example 6) Instead of Sr _1.0 Al ₁₂ O _x powder, Sr _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _0.8 La _0.2 Cr _1.0 Al ₁₁ O _X powder was used. (Example 7) Instead of Sr _1.0 Al ₁₂ O _x powder, Sr _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _0.8 La _0.2 Fe _1.0 Al ₁₁ O _x powder was used.

Example 8 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that Sr _0.8 La _0.2 Co _1.0 Al ₁₁ O _x powder was used instead of the Sr _1.0 Al ₁₂ O _x powder. It was (Example 9) Instead of Sr _1.0 Al ₁₂ O _x powder, Sr _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _0.8 La _0.2 Ni _1.0 Al ₁₁ O _X powder was used. Example 10 Instead of Sr _1.0 Al ₁₂ O _x powder, Ba
An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that _0.8 K _0.2 Mn _1.0 Al ₁₁ O _x powder was used.

Example 11 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that Ba _0.8 K _0.2 Cr _1.0 Al ₁₁ O _x powder was used in place of the Sr _1.0 Al ₁₂ O _x powder. It was (Example 12) Instead of Sr _1.0 Al ₁₂ O _x powder, Ba
An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that _0.8 K _0.2 Fe _1.0 Al ₁₁ O _x powder was used. Example 13 Instead of Sr _1.0 Al ₁₂ O _x powder, Ba
An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that _0.8 K _0.2 Co _1.0 Al ₁₁ O _X powder was used. (Example 14) Instead of Sr _1.0 Al ₁₂ O _x powder, Ba
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _0.8 K _0.2 Ni _1.0 Al ₁₁ O _x powder was used.

(Comparative Example 1) Rh-supported Sr _1.0 A was used in place of the Rh-supported Zr 3 wt% alumina powder (powder H).
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that l ₁₂ O _x (powder F) was used. (Comparative Example 2) An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that activated alumina was used instead of the Sr _1.0 Al ₁₂ O _x powder. (Comparative Example 3) Exhaust gas purification in the same manner as in Example 1 except that Rh-supported Ba _1.0 Al ₁₂ O _x (powder F) was used in place of the Rh-supported Zr 3 wt% alumina powder (powder H). A catalyst was obtained.

Comparative Example 4 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that activated alumina was used instead of the Ba _1.0 Al ₁₂ O _x powder. (Comparative Example 5) Instead of Sr _1.0 Al ₁₂ O _x powder, Sr _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _1.0 Mn _3.0 Al ₉ O _x powder was used. (Comparative Example 6) Instead of Ba _1.0 Al ₁₂ O _X powder, Ba _1.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that _1.0 Mn _3.0 Al ₉ O _x powder was used.

Rhodium and platinum in the exhaust gas purifying catalysts obtained in Examples 1 to 14 and Comparative Examples 1 to 6 were used.
Table 1 shows the contents of palladium, alkali metals and alkaline earth metals.

[0055]

[Table 1]

(Test Example) The exhaust gas purifying catalysts of Examples 1 to 14 and Comparative Examples 1 to 6 were subjected to durability treatment under the following durability conditions, and then catalytic activity was evaluated under the following evaluation conditions. [Durability conditions] Engine displacement 4400cc Fuel Leaded gasoline (Pb50mg / usg) Catalyst inlet gas temperature 950 ° 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%

[Evaluation condition 1: low temperature activity] Engine displacement 2000 cc Fuel unleaded gasoline Temperature rising rate 10 ° C./min Measurement temperature range 150 to 500 ° C. The low temperature activity of each exhaust gas purifying catalyst after endurance was evaluated as HC, C.
O and NO _X temperature when the conversion reached 50% (T5
0 / ° C.) and the results are shown in Table 2.

[0058]

[Table 2]

[0059] The purifying performance of the exhaust gas purifying catalyst after the durability test was determined HC, using Equation 1-3 below average conversion of CO and NO _X (%) of the stoichiometric atmosphere, and the results are shown in Table 3.

[0060]

[Equation 1]

[0061]

[Equation 2]

[0062]

(Equation 3)

[0063]

[Table 3]

[0064]

As described above, according to the present invention, the catalyst component-supporting layer contains hexaaluminate containing a specific element together with rhodium.
It is possible to provide an exhaust gas purification catalyst having improved durability and having excellent low temperature activity and purification performance even after high temperature durability.

That is, the exhaust gas purifying catalyst according to claim 1 has excellent durability at high temperatures, and can improve exhaust gas purifying performance such as low temperature activity and stoichiometric conversion after endurance. In addition to the above effects, the exhaust gas purifying catalyst according to claim 2 can further improve the structural stability at high temperatures. Further, in addition to the above effects, the exhaust gas purifying catalyst according to claim 3 can maintain / improve the catalyst performance from the initial stage to the end of durability and improve the coating property of the catalyst layer.

Further, in addition to the above effects, the exhaust gas purifying catalyst according to claim 4 can suppress the deterioration of the catalyst performance due to the reduction of the catalyst component. Furthermore, in addition to the above effects, the exhaust gas purifying catalyst according to claim 5 further improves low-temperature activity and purification performance, and can suppress deterioration of catalyst performance due to reduction of the catalyst component. Furthermore, in addition to the above effects, the exhaust gas purifying catalyst according to claim 6 can suppress sintering of palladium in the catalyst component and further improve low temperature activity and purifying performance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01J 23/58 B01D 53/36 104A 23/652 B01J 23/56 301A 23/656 23/64 103A 104A

Claims (8)

[Claims] 1. A monolithic structure catalyst comprising a monolithic structure carrier provided with a catalyst component supporting layer, which contains at least rhodium and hexaaluminate as catalyst components, and the hexaaluminate is nickel, cobalt, iron or manganese. An exhaust gas purifying catalyst containing at least one selected from the group consisting of chromium, potassium, strontium, barium and lanthanum. 2. The hexaaluminate is of the general formula [X] _a [Y] _b Al _12-b O _c , where X is selected from the group consisting of potassium, strontium, barium and lanthanum. At least one element, Y is at least one element selected from the group consisting of nickel, cobalt, iron, manganese, and chromium, a, b and c represent the atomic ratio of each element, a
= 1.0, b = 0 to 1.0, and c is the number of oxygen atoms required to satisfy the valences of the above components), and the exhaust gas according to claim 1. Purification catalyst. 3. The total rhodium amount is 1 to 70 in terms of metal.
3. The exhaust gas purifying catalyst according to claim 1, wherein the hexaaluminate is loaded with rhodium in a weight percentage. 4. A zirconium oxide is further contained, and one zirconium oxide selected from the group consisting of cerium, neodymium and lanthanum is 1 to 40 in terms of metal.
The exhaust gas-purifying catalyst according to any one of claims 1 to 3, which contains mol% and zirconium in an amount of 60 to 98 mol%. 5. The exhaust gas purifying catalyst according to any one of claims 1 to 4, further comprising at least one selected from the group consisting of palladium and platinum. 6. Alumina and cerium oxide are further contained, and the alumina is at least one selected from the group consisting of cerium, zirconium and lanthanum in an amount of 1 to 10 mol% in terms of metal, and activated alumina. 6. The cerium oxide contains at least one selected from the group consisting of zirconium, neodymium and lanthanum in an amount of 1 to 40 mol% and 60 to 98 mol% of cerium in terms of metal. Exhaust gas purification catalyst described. 7. The exhaust gas purifying apparatus according to claim 1, further comprising at least one selected from the group consisting of alkali metals and alkaline earth metals. catalyst. 8. The catalyst component layer containing palladium is arranged on the inner layer side of the coat layer in the monolithic structure type carrier, and rhodium and platinum are arranged on the surface layer side of the coat layer. The exhaust gas purifying catalyst according to any one of items 1 to 7.