JP3426792B2 - Exhaust gas purification catalyst - Google Patents

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. Specifically, carbon monoxide (CO), hydrocarbons (CH), and nitrogen oxides (N), which are harmful components contained in exhaust gas from internal combustion engines such as automobiles, are included.
The present invention relates to an exhaust gas purifying catalyst having excellent heat resistance and capable of simultaneously removing O _x ).

[0002]

2. Description of the Related Art Conventionally, carbon monoxide (CO) and hydrocarbons (C) which are harmful components in exhaust gas discharged from an internal combustion engine.
In a three-way catalyst for simultaneously removing H) and nitrogen oxides (NO _x ), platinum group elements such as platinum and rhodium and cerium oxide having an oxygen storage effect for improving low temperature activity are mainly used.

In such an exhaust gas purifying catalyst, a monolithic monolithic carrier is coated with a slurry of activated alumina and then impregnated with a cerium solution, and then a platinum group element-containing solution such as platinum or rhodium is used. Contained and supported to form a catalyst layer. Recently, high temperature heat resistance of the catalyst is required due to the tendency that the location of the exhaust gas purifying catalyst is directly below the manifold closer to the engine and the temperature of the exhaust gas rises during high speed operation.

However, the catalyst containing the white metal element and cerium oxide is easily deteriorated at high temperature. Therefore, in order to improve high temperature heat resistance, oxides of rare earth elements and alkaline earth metals are added to the catalyst supporting layer. A catalyst in which platinum is supported on cerium oxide in order to suppress platinum sintering is disclosed in Japanese Utility Model Publication No. 5-20435.

Further, Japanese Patent Publication No. 5-36098 discloses a noble metal composed of platinum and / or palladium,
When carrying rhodium and refractory inorganic oxide powder, after carrying rhodium, carrying noble metal, or after carrying noble metal, a slurry using the refractory inorganic oxide powder carrying rhodium is integrally structured Disclosed is a method of manufacturing a honeycomb catalyst for purifying exhaust gas, which is coated on a honeycomb carrier having:

[0006]

However, although the conventional three-way catalyst as described above shows good activity of the three-way catalyst at the initial stage, it has a high temperature and a large fluctuation in the gas atmosphere, such as directly under the manifold. In the case of being exposed to, the sintering of the catalyst components platinum and palladium occurred, which was not always sufficient in terms of exhaust gas purification performance.

The present invention has been made in view of the above circumstances, and in a three-way catalyst using platinum, palladium, and rhodium as catalyst components, CO, HC, and NO _x
It is an object of the present invention to provide an exhaust gas purifying catalyst having excellent heat resistance, which enables stable purification of the components not only in the initial stage but also over a long period of time.

[0008]

As a result of intensive studies to solve this problem, the present inventors carried out an activity supporting platinum, palladium and rhodium, which are metal catalysts having a total amount of 5% by weight or less. By forming a catalyst layer containing alumina and cerium oxide stabilized with zirconium as main components, an exhaust gas purifying catalyst having excellent heat resistance and durability was found and the present invention was completed.

The exhaust gas purifying catalyst of the present invention comprises 1 to 5% by weight of a metal catalyst of platinum and rhodium, palladium and rhodium, or platinum, palladium and rhodium, and a catalyst-supporting activated alumina, zirconium or zirconium and a rare earth. and an element (where cerium is excluded) and de-stabilized cerium oxide, and a refractory inorganic oxide containing the active alumina, and a catalyst layer formed in a more composed mixture, catalyst carrying the catalyst layer on the surface It is characterized by comprising a carrier.

The catalyst-supported activated alumina referred to herein is composed of a metal catalyst and activated alumina, and means that the metal catalyst accounts for 1 to 5% by weight of the total amount of the metal catalyst and activated alumina. . The exhaust gas purifying catalyst of the present invention comprises a catalyst-supported activated alumina carrying a small amount of a metal catalyst of 1 to 5% by weight, cerium oxide stabilized with zirconium or zirconium and a rare earth element (hereinafter referred to as stabilized cerium oxide). ) And a refractory inorganic oxide mixture. When the amount of the metal catalyst supported on the activated alumina is regulated to a small amount and mixed with the stabilized cerium oxide, the sintering of the metal catalyst in the catalyst layer is prevented and the stability of the metal catalyst by the stabilized cerium oxide is prevented. Can be realized. As a result, the heat resistance of the metal catalyst can be improved and the purifying effect can be sufficiently exerted.

If the total amount of the metal catalyst supported on the catalyst-support activated alumina exceeds 5% by weight, the purification performance will be deteriorated, which is not preferable. If the total amount of the activated alumina supported on the metal catalyst is less than 1% by weight, the catalytic activity is low and it cannot be used for practical use, which is not preferable. The amount of the metal catalyst supported on the activated alumina is preferably platinum, palladium except rhodium, and 0.9 to 4.9% by weight of platinum and palladium. On the other hand, rhodium is 0.1 to 1.0% by weight
It is preferably carried.

When the amount of platinum, palladium, or platinum and palladium supported is less than 0.9 g, sufficient catalytic activity may not be obtained, which is not preferable. On the other hand, if it exceeds 4.9 g, the catalyst activity will decrease if the amount of platinum and palladium supported is further increased, which is not preferable. The amount of rhodium supported on the activated alumina is preferably 0.1 to 1.0 g. When the supported amount of rhodium is less than 0.1 g, sufficient catalytic activity may not be obtained, which is not preferable. On the other hand, if it exceeds 1.0 g, even if the amount of rhodium carried is further increased, the activity is not improved so much and it is not preferable.

The loading amount of platinum, palladium, and platinum and palladium is 0.1 to 3.0 g / unit volume of the catalyst.
It is preferably liter. When the loading amount of platinum, palladium, or platinum and palladium is less than 0.1 g / liter, sufficient catalytic activity may not be obtained, which is not preferable. On the other hand, if it exceeds 3.0 g / liter, even if the supported amount is further increased, the activity is slightly improved and it is not preferable. In particular, the supported amount is 0.3 to 3.0 g /
The case of liter is more preferable in terms of the balance between activity and cost.

The amount of rhodium supported is preferably 0.01 g / liter per unit volume of the catalyst. If the amount of rhodium supported is less than 0.01 g / liter, sufficient catalytic activity may not be obtained. Also, 1. g /
If it exceeds liter, even if the supported amount of rhodium is further increased, the activity is slightly improved and it is expensive, which is not preferable. In particular, the case where the supported amount is 0.05 to 0.5 g / liter is more preferable in terms of the balance between activity and cost.

The activated alumina carrying the metal catalyst preferably has an average particle size of 10 μm or less and a specific surface area of 50 m ² / g or more. The amount of catalyst-supporting activated alumina in the catalyst layer is preferably in the range of 10 to 50% by volume. If the amount of the activated alumina is less than 10% by volume, a sufficient purifying action is not exhibited, which is not preferable. Further, if the amount of the catalyst-supported activated alumina added exceeds 50% by volume, the amount of the stabilized cerium oxide decreases and the effect of the stabilized cerium oxide decreases, which is not preferable.

The stabilized cerium oxide in which Ru enhances the heat resistance of the catalyst and cerium <br/> arm oxide, average particle size is 10
More preferably, it is less than or equal to μm. As the stabilized cerium oxide, a complex oxide or solid solution of zirconium oxide and rare earth element oxide is used. The composition of the stabilized cerium oxide is such that zirconium is 0.05 to 0.35, rare earth elements are 0 to 0.30, the total amount of zirconium and rare earth elements is 0.05 to 0.55, and the balance is cerium. It is desirable to configure so that

The stabilized cerium oxide is added to the catalyst layer in an amount of 20
It is desirable to occupy 70% by weight. Stabilized cerium
The oxide is calcined in air at 900 ° C. for 5 hours, for example.
20m specific surface area after²/ G or more
Is desirable. Note that commercially available cerium oxide is empty.
Specific surface area after firing at 900 ° C for 5 hours in air is 10m
²/ G or less, which is not preferable.

The stabilized cerium oxide is formed by the following adjusting method, but the adjusting method is not particularly limited. For example, a method of supporting a commercially available cerium oxide with a water-soluble zirconium salt or a zirconium salt and a rare earth element salt other than cerium, a water-soluble cerium salt, a zirconium salt or a zirconium salt and a rare earth element salt other than cerium are mixed and dried. After that, a method of firing, a method of mixing a water-soluble cerium salt, a zirconium salt, or a zirconium salt and a rare earth element salt other than cerium and then supporting the mixture on a refractory inorganic oxide can be mentioned. The salts of cerium, zirconium, and rare earth elements other than cerium used are not particularly limited, and commercially available nitrates, acetates, sulfates, chlorides and the like can be used.

The refractory inorganic oxide is preferably activated alumina or activated alumina stabilized with a rare earth element such as lanthanum, an alkaline earth metal such as magnesium or barium, silicon and / or an oxide thereof. This catalyst layer can be formed by, for example, supporting the surface of a catalyst carrier by using a slurry of a mixture of the above-mentioned catalyst-supporting activated alumina, stabilized cerium, and a refractory inorganic oxide, and firing it. Thereby, the catalyst layer, the activated alumina supporting the metal catalyst, the stabilized cerium oxide, and the refractory inorganic oxide are uniformly dispersed in the catalyst layer,
The low-concentration metal catalyst supported on the catalyst-supporting activated alumina can prevent sintering by the stabilized cerium oxide and can improve heat resistance to exert a purifying effect.

In addition, a part of the metal catalyst may be supported by, for example, dipping in the catalyst layer after forming the catalyst layer so that the distribution of the metal catalyst is increased only on the surface portion of the catalyst layer to further improve the purification performance. it can. Furthermore, when the catalyst layer is formed by separately adjusting activated alumina supporting platinum or platinum and palladium and activated alumina supporting rhodium, the metal catalyst is widely distributed in the catalyst layer, each of which works effectively and is stable. The cerium oxide can prevent the metal catalyst from being deteriorated due to heat, etc., and can enhance the exhaust gas purification performance.

The catalyst for purifying exhaust gas of the present invention is produced, for example, by using activated alumina carrying platinum and rhodium, palladium and rhodium, platinum and palladium and rhodium, stabilized cerium oxide and refractory inorganic oxide. The catalyst layer is formed by adhering and supporting the slurry with the mixture on the surface of the catalyst carrier. In some cases, the catalyst layer may be further immersed in a metal catalyst solution to support the metal catalyst on the surface portion of the catalyst layer to further enhance the purification activity. Further, activated alumina supporting platinum and palladium and activated alumina supporting rhodium may be separately prepared and mixed in a slurry to form a catalyst layer. However, even in this case, the total amount of the metal catalyst supported on the activated alumina is within the above range of 5% by weight.

[0022]

In the exhaust gas purifying catalyst of the present invention , the catalyst layer is either platinum and rhodium, platinum and palladium and rhodium, or 1 to 5% by weight of palladium and rhodium, and activated cerium oxide. And a refractory inorganic oxide, and is formed on the surface of the catalyst carrier. For this reason, the activated alumina supporting the metal catalyst and the stabilized cerium oxide are widely distributed in the catalyst layer, respectively, and the metal catalyst and the stabilized cerium oxide do not exist in agglomeration, and the metal catalyst and the stabilized cerium oxide perform the functions of each other. Sintering of platinum, palladium and rhodium can be significantly suppressed even in places with high temperature and large fluctuations in gas atmosphere, and has HC, CO, and NO _x purification activity, heat resistance, and durability. It becomes an excellent exhaust gas purifying catalyst. Further, the exhaust gas purifying catalyst of the present invention is made of platinum or para.
An active catalyst that supports platinum or platinum and palladium.
Activated alumina supporting lumina and rhodium in slurry
When mixed to form a catalyst layer, the metal
Since it is widely distributed by itself, it exerts sufficient catalytic performance and is relatively low.
The purification performance can be shown even in the concentration.

In the exhaust gas purifying catalyst of the present invention , a part of at least one noble metal selected from platinum, palladium and rhodium in the catalyst layer is supported on the catalyst layer with a solution, for example, without changing the total supported amount. platinum, to pass within 100μm from the surface of the catalyst layer is palladium, since the rhodium can be supported within 40μm from the surface of the catalyst layer, the purification performance of the NO _X in the surface layer may more efficiently high Mel things.

The exhaust gas purifying catalyst of the present invention can exhibit an effective purifying action when the amount of activated alumina carrying the catalyst is in the small range of 10 to 50% by volume in the catalyst layer.

[0025]

The present invention will be described below with reference to examples, but the scope of the present invention is not limited to these examples. (Example 1) An average particle size of 5.0 μm and a specific surface area of 200 m ²
/ G of activated alumina powder was dipped in an aqueous dinitrodiammine platinum solution and an aqueous rhodium nitrate solution, dried and pulverized to 5
It was calcined at 00 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder in which 2% by weight of platinum and 0.4% by weight of rhodium were supported on activated alumina.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and an aqueous solution of zirconium oxynitrate were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide is 5/1 at a cerium / zirconium molar ratio.
Met. Next, 400 cells / in ² , diameter 80 mm,
A cordierite monolith carrier with a length of 95 mm,
A catalyst-supported activated alumina powder supporting 2% by weight of the platinum and 0.4% by weight of rhodium prepared above and the stabilized cerium oxide powder were added to the activated alumina powder as a refractory inorganic oxide, and an alumina hydrate. The slurry prepared by adding pure water and pure water is coated and dried, and then baked at 500 ° C. for 1 hour to form a catalyst layer composed of platinum, rhodium, cerium, zirconium and activated alumina on the surface of the carrier. It was designated as catalyst 1. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Further, the cross section of the catalyst layer of the catalyst 1 is shown in EPMA (el
ectron probe microanalysis), platinum, rhodium, cerium and zirconium were distributed throughout the catalyst layer.

[0028]

[Table 1]

Example 2 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous dinitrodiammine platinum solution and an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour. A catalyst-supported activated alumina powder supporting 2% by weight of platinum and 0.2% by weight of rhodium with respect to activated alumina was obtained.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and an aqueous solution of zirconium oxynitrate were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide is 5/1 at a cerium / zirconium molar ratio.
Met. Next, using the same monolithic carrier as used in Example 1, 2% by weight of platinum and rhodium of 0.
A catalyst-supported activated alumina powder supporting 2% by weight and a cerium oxide powder stabilized with the zirconium,
A slurry prepared by adding activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water was coated and dried, and then baked at 500 ° C. for 1 hour to give a monolith carrier.
A catalyst layer of platinum, rhodium, cerium, zirconium and activated alumina was formed. Further, the carrier was immersed in an aqueous solution of rhodium nitrate to carry rhodium to obtain a catalyst 2.
The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of the catalyst 2 was analyzed by EPMA, platinum, rhodium, cerium and zirconium were found throughout the catalyst layer, and rhodium was 40 μm mainly from the surface.
Although it was distributed in m, it was confirmed that it was distributed in the deep part of the catalyst layer. (Example 3) Specific surface area of 200 m ² with an average particle size of 5.0 μm
/ G of activated alumina powder was dipped in an aqueous dinitrodiammine platinum solution and an aqueous rhodium nitrate solution, dried and pulverized to 5
It was calcined at 00 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder in which 2% by weight of platinum and 0.1% by weight of rhodium were supported on activated alumina.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and a zirconium oxynitrate aqueous solution were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide was 5/1 in terms of cerium / zirconium molar ratio. Next, using the same monolithic carrier as used in Example 1, 2% by weight of the platinum prepared above and rhodium 0.
A slurry prepared by adding 1% by weight of the catalyst-supported activated alumina powder and the stabilized cerium oxide powder to the activated alumina powder of the refractory inorganic oxide, alumina hydrate and pure water was coated and dried. And then at 500 ℃ 1
After firing for a period of time, platinum, rhodium, cerium,
A catalyst layer of zirconium and activated alumina was formed.
Further, this carrier was immersed in a rhodium nitrate solution to support rhodium on the catalyst layer to obtain catalyst 3. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of the catalyst 3 was analyzed by EPMA, platinum, rhodium, cerium and zirconium were found throughout the catalyst layer, and rhodium was 40 μm mainly from the surface.
Although it was distributed in m, it was confirmed that it was distributed in the deep part of the catalyst layer. (Comparative Example 1) A cordierite monolithic carrier similar to that of Example 1 was coated with a slurry of cerium-zirconium oxide powder, γ-alumina powder, alumina hydrate and pure water, and dried. Firing at 1 ° C. for 1 hour formed an alumina layer containing cerium-zirconium on the carrier. The carrier thus obtained was immersed in a dinitrodiammine platinum solution, dried, and then immersed in a rhodium nitrate solution to support rhodium to obtain a catalyst A.
The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of this catalyst A was analyzed by EPMA, platinum was distributed within 100 μm from the surface and rhodium was distributed within 40 μm from the surface. (Comparative Example 2) was added activated alumina dinitrodiammine platinum solution, dried and fired to obtain a platinum-containing activated alumina. The platinum content in this platinum-containing activated alumina was 2.0% by weight.
Met.

Next, a cordierite monolithic carrier similar to that used in Example 1 was added to platinum-containing activated alumina, cerium-
A slurry consisting of zirconium oxide powder, γ-alumina powder, alumina hydrate and pure water was coated, dried and calcined at 500 ° C. for 1 hour to form an alumina layer containing cerium-zirconium on a carrier. . The carrier thus obtained was further immersed in a rhodium nitrate solution to carry rhodium, thereby obtaining catalyst B. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

The 40μ catalyst layer cross-section of the catalyst B was analyzed by EP M A, platinum throughout, rhodium from the surface
It was distributed within m. Example 4 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous dinitrodiammine platinum solution and an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to obtain activated alumina. On the other hand, a catalyst-supported activated alumina powder carrying 1% by weight of platinum and 0.4% by weight of rhodium was obtained.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and a zirconium oxynitrate aqueous solution were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of the stabilized cerium oxide was 5/1 in terms of a cerium / zirconium molar ratio. Next, using the same monolith carrier as used in Example 1, 1% by weight of the platinum prepared above and 0.4 of rhodium were used.
After coating a slurry prepared by adding activated alumina powder of the refractory inorganic oxide, alumina hydrate and pure water to the catalyst-supported activated alumina powder and the stabilized cerium oxide powder supported by weight%, and drying. And calcination at 500 ° C. for 1 hour to form a catalyst layer of platinum, rhodium, cerium, zirconium and activated alumina on the carrier to form a catalyst 4
Got The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Example 5 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous solution of dinitrodiammine platinum and an aqueous solution of rhodium nitrate, dried, pulverized and calcined at 500 ° C. for 1 hour. A catalyst-supported activated alumina powder supporting 1% by weight of platinum and 0.2% by weight of rhodium with respect to activated alumina was obtained.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and a zirconium oxynitrate aqueous solution were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of the stabilized cerium oxide was 5/1 in terms of a cerium / zirconium molar ratio. Next, using the same monolith carrier as used in Example 1, 1% by weight of the platinum prepared above and 0.2 of rhodium were prepared.
A slurry prepared by adding activated alumina powder of the refractory inorganic oxide, alumina hydrate and pure water to the activated alumina powder supported by weight% and the stabilized cerium oxide powder is coated and dried, and then 500 It was calcined at 1 ° C. for 1 hour to form a catalyst layer of platinum, rhodium, cerium, zirconium and activated alumina on the monolith support. Further, this carrier was immersed in an aqueous solution of rhodium nitrate to support rhodium on the catalyst layer to obtain a catalyst 5. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Comparative Example 3 The same cordierite monolithic carrier as in Example 1 was coated with a slurry of cerium-zirconium oxide powder, γ-alumina powder, alumina hydrate and pure water and dried. After that, 1 at 500 ℃
It was calcined for a time to form an alumina layer containing cerium-zirconium on the carrier. The carrier thus obtained was dipped in a dinitrodiammine platinum solution, dried, and then dipped in a rhodium nitrate solution to support rhodium to obtain a catalyst C. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the coating layer of this catalyst was analyzed by EPMA, platinum was within 100 μm and rhodium was 40 μm.
It was distributed within m. (Comparative Example 4) A platinum-containing activated alumina was obtained by adding dinitrodiammine platinum solution to activated alumina powder, followed by drying and firing. The platinum content in this platinum-containing activated alumina is
It was 1.0% by weight.

Next, a cordierite monolithic carrier similar to that used in Example 1 was added to platinum-containing activated alumina, cerium-
A slurry consisting of zirconium oxide powder, γ-alumina powder, alumina hydrate and pure water was coated, dried and calcined at 500 ° C. for 1 hour to form an alumina layer containing cerium-zirconium on a carrier. . The carrier thus obtained was further dipped in a rhodium nitrate solution to carry rhodium, thereby obtaining catalyst D. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Example 6 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous dinitrodiammine platinum solution, an aqueous palladium nitrate solution and an aqueous rhodium nitrate solution, dried and pulverized at 500 ° C. for 1 hour. After time calcination, 1% by weight of platinum, 1% by weight of palladium and 0.4% by weight of rhodium were supported on the activated alumina to obtain a catalyst-supported activated alumina powder.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
After mixing ² / g of cerium oxide with an aqueous solution of zirconium oxynitrate and the rare earth element yttrium, and drying,
It was calcined at 500 ° C. for 1 hour to obtain a zirconium-stabilized cerium oxide powder. The composition of the zirconium-stabilized cerium oxide was 5/1/1 in the molar ratio of cerium / zirconium / rare earth element yttrium.

Next, using the same monolithic carrier as that used in Example 1, 1% by weight of the platinum prepared above, 1% by weight of palladium, and 0.4% by weight of rhodium were loaded on the catalyst-supported activated alumina powder and A slurry prepared by adding activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water to the stabilized cerium oxide powder was coated and dried, and then calcined at 500 ° C. for 1 hour, Catalyst 6 was obtained by forming a catalyst layer of platinum, rhodium, cerium, zirconium, yttrium, and activated alumina on the carrier.
The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the catalyst layer cross section of the catalyst 6 was analyzed by EPMA, it was confirmed that platinum, palladium, rhodium, cerium, yttrium and zirconium were distributed throughout the catalyst layer. (Example 7) An average particle size of 5.0 μm and a specific surface area of 200 m ²
/ G of activated alumina powder is dipped in dinitrodiammine platinum aqueous solution and rhodium nitrate aqueous solution, dried and crushed to 500
By calcination at 1 ° C. for 1 hour, a catalyst-supported activated alumina powder supporting 1% by weight of platinum and 0.4% by weight of rhodium with respect to activated alumina was obtained.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
After mixing ² / g of cerium oxide, zirconium oxynitrate and an aqueous solution of the rare earth element yttrium, and drying, 50
It was calcined at 0 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide is cerium / zirconium / rare earth element yttrium in a molar ratio of 5/1.
It was / 1.

Next, using the same monolithic carrier as used in Example 1, 1% by weight of the platinum prepared above and 0.4% by weight of rhodium were loaded on the activated alumina powder and the cerium stabilized with the zirconium. The oxide powder and activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water were added to the slurry to prepare a slurry, which was dried and then calcined at 500 ° C. for 1 hour to give a monolith carrier. A catalyst layer of platinum, rhodium, cerium, zirconium, yttrium and activated alumina was formed. Further, this carrier was immersed in an aqueous solution of palladium nitrate to support palladium on the catalyst layer to obtain a catalyst 7. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of the catalyst 7 was analyzed by EPMA, platinum, palladium, rhodium, cerium, yttrium and zirconium were distributed throughout the catalyst layer, and palladium was distributed within 100 μm from the surface layer. Was confirmed. (Example 8) Specific surface area of 200 m ² with an average particle size of 5.0 μm
/ G of activated alumina powder was dipped in an aqueous palladium nitrate solution and an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to support 1% by weight of palladium and 0.4% by weight of rhodium on the activated alumina. A catalyst-supported activated alumina powder was obtained.

Next, the average particle size is 5 μm and the specific surface area is 120 m.
After mixing ² / g of cerium oxide, zirconium oxynitrate and an aqueous solution of the rare earth element yttrium, and drying, 50
It was calcined at 0 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of the zirconium-stabilized cerium oxide was 5/1/1 in the molar ratio of cerium / zirconium / rare earth element yttrium.

Next, using the same monolithic carrier as used in Example 1, stabilized with the catalyst-supported activated alumina powder supporting 1% by weight of the palladium and 0.4% by weight of rhodium prepared above and the zirconium. Cerium oxide powder, activated alumina powder of refractory inorganic oxide, alumina hydrate, and pure water were coated on the slurry, dried, and then calcined at 500 ° C. for 1 hour to obtain a monolith carrier. Then, a catalyst layer of palladium, rhodium, cerium, zirconium, yttrium and activated alumina was formed. Further, this carrier was immersed in a dinitrodiammine platinum aqueous solution to support platinum on the catalyst layer to obtain a catalyst 8. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

[0052] Further, when the coating layer cross-section of the catalyst 8 was analyzed in EP M A, palladium, palladium, rhodium,
It was confirmed that cerium, yttrium and zirconium were distributed throughout the catalyst layer, and platinum was distributed within 100 μm from the surface layer. Comparative Example 5 The same cordierite monolithic carrier as in Example 1 was coated with a slurry of cerium-zirconium and oxide powder of rare earth element yttrium, γ-alumina powder, alumina hydrate and pure water. After drying, it was baked at 500 ° C. for 1 hour to form an activated alumina layer containing cerium-zirconium on the carrier. The carrier thus obtained was immersed in an aqueous solution of palladium nitrate and an aqueous solution of dinitrodiammineplatinum, dried, and further immersed in a solution of rhodium nitrate to support rhodium on the activated alumina-containing layer to obtain catalyst E. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

[0053] Analysis of coating layer cross-section of the catalyst in the EP M A, platinum, palladium in 100 [mu] m, rhodium was distributed in 40 [mu] m. (Comparative Example 6) A dinitrodiammine platinum solution and an aqueous palladium nitrate solution were added to activated alumina powder, dried, pulverized, and then calcinated at 500 ° C for 1 hour to obtain 1.0% by weight of platinum and 1.
A catalyst-supported activated alumina powder supporting 0% by weight was obtained.

Next, on a cordierite monolithic carrier similar to that used in Example 1, platinum, palladium-containing activated alumina, oxide powder of cerium-zirconium rare earth element yttrium and γ-alumina powder, alumina hydrate and pure water were used. After coating and drying the slurry consisting of
After firing for a while, platinum, palladium, cerium,
An activated alumina layer containing yttrium and zirconium was formed. The carrier thus obtained was further immersed in an aqueous solution of rhodium nitrate to support rhodium on the activated alumina layer to obtain a catalyst F. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Example 9 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous solution of palladium nitrate and an aqueous solution of rhodium nitrate, dried and then pulverized.
It was calcined at 00 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder supporting 2% by weight of palladium and 0.4% by weight of rhodium with respect to activated alumina.

Then, a cerium oxide powder stabilized with zirconium was obtained in the same manner as in Example 1. The composition of this stabilized cerium oxide was 5/1 in terms of cerium / zirconium molar ratio. Next, using the same monolith carrier as used in Example 1, the palladium 2 prepared above was used.
%, Rhodium 0.4% by weight, catalyst-supported active alumina powder and cerium oxide powder stabilized with the zirconium, active alumina powder of refractory inorganic oxide, alumina hydrate and pure water were added. The slurry prepared as described above was coated and dried, and then calcined at 500 ° C. for 1 hour to form a catalyst layer of platinum, rhodium, cerium, zirconium and activated alumina on the carrier to obtain a catalyst 9.
The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of the catalyst 9 was analyzed by EPMA, palladium, rhodium, cerium and zirconium were distributed throughout the catalyst layer. (Example 10) An average particle size of 5.0 μm and a specific surface area of 200 m
² / g of activated alumina powder was dipped in an aqueous solution of palladium nitrate and an aqueous solution of rhodium nitrate, dried and pulverized to 500 ° C.
Then, it was calcined for 1 hour to obtain a catalyst-supported activated alumina powder supporting 2% by weight of palladium and 0.2% by weight of rhodium with respect to the activated alumina.

Then, a cerium oxide powder stabilized with zirconium was obtained in the same manner as in Example 1. The composition of this stabilized cerium oxide was 5/1 in terms of cerium / zirconium molar ratio. Next, using the same monolithic carrier as that used in Example 1, activated alumina powder supporting 2% by weight of palladium and 0.2% by weight of rhodium prepared above and cerium oxide powder stabilized with zirconium. And a slurry prepared by adding activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water, and drying, and then firing at 500 ° C. for 1 hour to form palladium, rhodium, on a monolith carrier. A catalyst layer of cerium, zirconium and activated alumina was formed. further,
This carrier was immersed in an aqueous solution of rhodium nitrate to support rhodium on the catalyst layer to obtain a catalyst 10. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Comparative Example 7 The same cordierite monolithic carrier as in Example 1 was coated with a slurry of cerium-zirconium oxide powder, γ-alumina powder, alumina hydrate and pure water and dried. After that, 1 at 500 ℃
It was calcined for a time to form an alumina layer containing cerium-zirconium on the carrier. The monolithic support thus obtained was immersed in an aqueous solution of palladium nitrate, dried, and further immersed in an aqueous solution of rhodium nitrate to carry rhodium, thereby obtaining catalyst G. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of this catalyst G was analyzed by EPMA, palladium was distributed within 100 μm and rhodium was distributed within 40 μm. (Comparative Example 8) An aqueous palladium nitrate solution was added to activated alumina powder, dried, pulverized, and calcined at 500 ° C for 1 hour to obtain activated alumina powder carrying 2.0% by weight of palladium.

Next, the same cordierite monolithic carrier as in Example 1 was coated with a slurry containing palladium-containing activated alumina, cerium-zirconium oxide powder and γ-alumina powder, alumina hydrate and pure water. After drying, it was baked at 500 ° C. for 1 hour to form an alumina layer containing palladium and cerium-zirconium on the carrier. The carrier thus obtained was further immersed in an aqueous rhodium nitrate solution to carry rhodium, thereby obtaining a catalyst H.
The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

Example 11 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was dipped in an aqueous dinitrodiammine platinum solution, dried and pulverized at 500 ° C. for 1 hour.
It was calcined for a period of time to obtain activated alumina powder in which 2% by weight of platinum was supported on activated alumina. Next, average particle size 5.0 μm
Then, activated alumina powder having a specific surface area of 200 m ² / g was immersed in an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder carrying 0.4% by weight of rhodium. .

Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and a zirconium oxynitrate aqueous solution were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide was 5/1 in terms of cerium / zirconium molar ratio. Next, using the same monolithic carrier as used in Example 1, 2% by weight of the platinum prepared above and rhodium 0.
A catalyst-supported activated alumina powder supporting 4% by weight and a cerium oxide powder stabilized with the zirconium,
A slurry made by adding activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water was coated and dried, and then calcined at 500 ° C. for 1 hour to obtain platinum, rhodium, cerium or zirconium on a carrier. And a catalyst layer of activated alumina was formed to obtain a catalyst 11. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

When the cross section of the catalyst layer of the catalyst 11 was analyzed by EPMA, platinum, rhodium, cerium and zirconium were distributed throughout the catalyst layer. (Example 12) Average particle size 5.0 μm, specific surface area 200
m ² / g of activated alumina powder was immersed in a dinitrodiammine platinum aqueous solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to obtain activated alumina powder carrying 2% by weight of platinum with respect to activated alumina.

Next, with an average particle size of 5.0 μm and a specific surface area of 2
00 m ² / g of activated alumina powder was dipped in a rhodium nitrate aqueous solution, dried, pulverized and fired at 500 ° C. for 1 hour to obtain activated alumina powder carrying 0.2% by weight of rhodium. Next, cerium oxide having an average particle size of 5 μm and a specific surface area of 120 m ² / g and an aqueous solution of zirconium oxynitrate were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide was 5/1 in terms of cerium / zirconium molar ratio.

Next, using the same monolith carrier as used in Example 1, the catalyst-supported activated alumina powder supporting 2% by weight of platinum and 0.2% by weight of rhodium prepared above and stabilized with the zirconium were prepared. Cerium oxide powder, activated alumina powder of refractory inorganic oxide, alumina hydrate, and pure water were coated on a slurry, dried, and then calcined at 500 ° C. for 1 hour to obtain a carrier. , Platinum, rhodium, cerium, zirconium, and activated alumina catalyst layers were formed. Further, this carrier was immersed in an aqueous solution of rhodium nitrate to support rhodium on the catalyst layer to obtain a catalyst 12. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

The cross section of the catalyst layer of the catalyst 12 is EPMA.
As a result, it was confirmed that platinum, cerium and zirconium were distributed throughout the catalyst layer and rhodium was distributed mainly within 40 μm from the surface, but was also distributed in the deep part of the catalyst layer. (Example 13) Average particle size 5.0 μm, specific surface area 200
m ² / g of activated alumina powder was immersed in a dinitrodiammine platinum aqueous solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder having 2% by weight of platinum supported on the activated alumina.

Next, with an average particle size of 5.0 μm and a specific surface area of 2
00 m ² / g of activated alumina powder was immersed in an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to obtain a catalyst-supported activated alumina powder carrying 0.1% by weight of rhodium. Next, the average particle size is 5 μm and the specific surface area is 120 m.
² / g of cerium oxide and an aqueous solution of zirconium oxynitrate were mixed, dried and then calcined at 500 ° C. for 1 hour to obtain a stabilized cerium oxide powder. The composition of this stabilized cerium oxide is 5/1 at a cerium / zirconium molar ratio.
Met.

Next, using the same monolithic carrier as used in Example 1, the catalyst-supported activated alumina powder supporting 2% by weight of platinum prepared above and the catalyst-supported active alumina supporting 0.2% by weight of rhodium were prepared. The powder and the zirconium-stabilized cerium oxide powder were coated with a slurry prepared by adding activated alumina powder of a refractory inorganic oxide, alumina hydrate and pure water, and dried, and then 500
The catalyst layer of platinum, rhodium, cerium, zirconium and activated alumina was formed on the carrier by firing at 1 ° C. for 1 hour. Further, this carrier was immersed in an aqueous solution of rhodium nitrate to support rhodium on the catalyst layer to obtain a catalyst 13. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.
Shown in.

[0070] Moreover, the cross section of the catalyst layer of the catalyst 1 3 EPMA
As a result, it was confirmed that platinum, cerium and zirconium were distributed throughout the catalyst layer and rhodium was distributed mainly within 40 μm from the surface, but was also distributed in the deep part of the catalyst layer. Comparative Example 9 Activated alumina powder having an average particle size of 5.0 μm and a specific surface area of 200 m ² / g was immersed in an aqueous dinitrodiammine platinum solution and an aqueous rhodium nitrate solution, dried, pulverized, and calcined at 500 ° C. for 1 hour to be active. A catalyst-supported activated alumina powder supporting 5% by weight of platinum and 0.4% by weight of rhodium with respect to alumina was obtained.

Then, a cerium oxide powder stabilized with zirconium was obtained in the same manner as in Example 1. The zirconium-stabilized cerium oxide had a cerium / zirconium molar ratio of 5/1. next,
Using the same monolith carrier as used in Example 1, 400
Cell / in ² , 80 mm diameter, 95 mm length of cordierite monolithic carrier loaded with 5 wt% platinum and 0.4 wt% rhodium on a catalyst-supported activated alumina powder and cerium stabilized with zirconium. After coating the oxide powder with a slurry of activated alumina powder of refractory inorganic oxide, alumina hydrate and pure water and drying, 5
The mixture was calcined at 00 ° C. for 1 hour to form a catalyst layer composed of platinum, rhodium, cerium, zirconium and activated alumina on the monolith support to obtain a catalyst I. The composition and amount of this metal catalyst and the stabilized cerium oxide are shown in Table 1.

(Evaluation) Examples 1 to 13 and Comparative Examples 1 to 1
The catalyst obtained in No. 9 was attached to a 4000 cc engine and the aging conditions shown in FIG.
Endurance test was conducted at 50 ° C. for 50 hours at 1050 ° C. in the floor.
Exhaust gas purification rate after endurance test is running in 10/15 mode in vehicle equipped with engine of 660cc, HC, CO, N
The emission of O _X was measured. The results are shown in Table 2 as the purification rate.

[0073]

[Table 2]

As is clear from Table 2, the exhaust gas purification rates after the durability test were as follows: Catalysts 1, 2, 3 and A, B. 4, 5 and C,
D. 6, 7, 8 and E, F, 9, 10 and G, H, 11, 1
2,13 and A, also Izure and comparing and B towards the catalyst of Example shows that HC, CO, the discharge amount is small purification rate of the NO _X are better than the comparative catalyst. Further, the catalyst-supported activated alumina of Comparative Example 9 contained 5% by weight or more (5.
4% by weight), the purification rate was lower than in the case of this example.

Further, Examples 2 and 3 and Comparative Example 2
XRD was used to determine the particle size of platinum after the endurance test and the palladium particle size after the endurance test of the catalysts of Example 10 and Comparative Example 8.
It was measured by (X-ray diffraction). The results are shown in Table 3.

[0076]

[Table 3]

Further, from Table 3 , catalyst 2, catalyst 3 and catalyst 10 are catalyst B of which the particle diameters of platinum and palladium are comparative examples.
And less than that of catalyst H. This shows that the catalyst of the present invention suppresses sintering of platinum and palladium.

[0078]

Since the exhaust gas purifying catalyst of the present invention is excellent in durability and heat resistance at high temperatures, it can be used at a high temperature such as directly below the manifold and in which the gas atmosphere fluctuates drastically. Can be maintained.

[Brief description of drawings]

FIG. 1 is a chart showing aging conditions of a durability test.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Taki, 7800 Chihama, Daito-cho, Ogasa-gun, Shizuoka Within Cataler Industry Co., Ltd. Company Shiga Technical Center (72) Inventor Koji Yamada 3000 Yamanoue, Ryuo-cho, Gamo-gun, Shiga Prefecture Daihatsu Industry Co., Ltd. Shiga Technical Center (56) Reference JP-A-6-233918 (JP, A) -114742 (JP, A) JP-A-63-20036 (JP, A) JP-A-2-198636 (JP, A) JP-A-3-131343 (JP, A) JP-A-63-229145 (JP, A) ) JP-A-64-27643 (JP, A) JP-A-64-58347 (JP, A) JP-A-8-38897 (JP, A) Actual development Sho-64-39825 (JP, U) (58) adjustment Fields examined (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (9)

(57) [Claims] 1. A catalyst-supporting activated alumina carrying 1 to 5% by weight of a metal catalyst of platinum and rhodium, palladium and rhodium, or platinum and palladium and rhodium, zirconium or zirconium and a rare earth element (excluding cerium). and in stabilized cerium oxide, and a refractory inorganic oxide containing the active alumina, and a catalyst layer formed in a more composed mixture, and characterized by comprising a catalyst carrier carrying the catalyst layer on the surface Exhaust gas purification catalyst. 2. Cerium stabilized with platinum, palladium or a catalyst-supported active alumina supporting platinum and palladium, a catalyst-supporting active alumina supporting rhodium, zirconium or zirconium and a rare earth element (excluding cerium). an oxide, a refractory inorganic oxide containing the active alumina consists of a catalyst layer formed in a more composed mixture, a catalyst carrier carrying the catalyst layer on the surface, which is supported on the catalyst supporting activated alumina The exhaust gas purifying catalyst is characterized in that the metal catalyst is 1 to 5% by weight. 3. The exhaust gas purifying catalyst according to claim 1, wherein a part of rhodium of the metal catalyst is carried on the catalyst layer after the catalyst layer is formed. 4. The exhaust gas purifying catalyst according to claim 1, wherein after the catalyst layer is formed, platinum, palladium, or a part of platinum and palladium of the metal catalyst is supported on the catalyst layer. 5. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst-supported activated alumina is 10 to 50% by volume of the catalyst layer. 6. The amount of platinum and the amount of platinum and palladium supported is 0.1 to 3.0 g / liter per unit volume of the catalyst, and the amount of rhodium is 0.01 per unit volume of the catalyst. The catalyst for purifying exhaust gas according to claim 1, 2 or 5, which has a content of ˜1.0 g / liter. 7. The exhaust gas purifying apparatus according to claim 1, wherein the platinum, the palladium, and the platinum and the palladium are supported in an amount of 0.9 to 4.9% by weight based on the catalyst-supporting activated alumina. catalyst. 8. The exhaust gas purifying catalyst according to claim 1, wherein the amount of the rhodium supported is 0.1 to 1.0% by weight of the catalyst-supporting activated alumina. 9. The stabilized cerium oxide is 20-70% by weight of the catalyst layer.
The exhaust gas purifying catalyst according to 1.