JPH06114264A - Production of catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst excellent in purifying performance for exhaust gas after the catalyst is endured against high temp. by preparing an alumina powder with deposition of cerium and zirconium from a suspension liquid containing water-soluble cerium salt, water-soluble zirconium salt, and active alumina powder, carrying platinum or palladium on the powder, and then forming a catalyst coating layer. CONSTITUTION:This catalyst is a monolithic catalyst for purification of exhaust gas and the catalyst coating layer consists of platinum and rhodium or palladium and contains active alumina, cerium and zirconium. An alumina powder carrying cerium and zirconium is obtd. by precipitation reaction of a suspention liquid containing water-soluble cerium salt, water-soluble zirconium salt, and active alumina powder. Proportion of metal atoms to constitute the alumina powder carrying cerium and zirconium is cerium:zirconium:aluminum = (5 to 15):(1 to 4):100. Further, platinum or palladium is carried on the alumina powder carrying cerium and zirconium and then the catalyst coating layer is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for purifying exhaust gas discharged from an internal combustion engine such as an automobile. For more details,
Hydrocarbon (HC) which is a harmful component in exhaust gas discharged from internal combustion engines such as automobiles for the purpose of preventing air pollution,
The present invention relates to a method for producing an exhaust gas purifying catalyst that purifies carbon monoxide (CO) and nitrogen monoxide (NO _x ) simultaneously.

[0002]

2. Description of the Related Art Conventionally, various exhaust gas purifying catalysts for purifying harmful components in exhaust gas discharged from an internal combustion engine have been proposed. For example, as disclosed in JP-A-63-162043, a catalyst obtained by forming an activated alumina layer on a monolith carrier and then impregnating and supporting cerium and zirconium with an aqueous nitrate solution or the like, or JP-A-57-8783.
No. 9, JP-A-61-157347 and JP-A-1-1.
As disclosed in No. 23636, there has been proposed a catalyst in which oxides or carbonates of cerium and zirconium are mixed with alumina or activated alumina and applied as a slurry to a monolith carrier.

[0003]

However, in the conventional method for adding cerium and zirconium to alumina in such a catalyst for purification of exhaust gas, the oxide or carbonate powder of cerium or zirconium is activated alumina powder. In the method of heat treatment by mixing with
Since both oxides are difficult to form a composite, there is a problem that the effect of improving the oxygen storage capacity of ceria by adding zirconium cannot be expected and sufficient improvement of the catalytic performance cannot be recognized.
Further, in the method of heat treatment by impregnating and adding cerium and zirconium to an aqueous solution of nitrate such as activated alumina, or a monolith carrier after forming an activated alumina layer,
Since cerium and zirconium are supported on the micropores and micropores of activated alumina, there is also a problem that if the addition amount is large, the pore structure of these is blocked and sufficient improvement of catalyst performance cannot be observed.

Accordingly, it is an object of the present invention to provide a method for producing an exhaust gas purifying catalyst which has a high purifying performance even before and after the endurance under severe conditions such as a high temperature atmosphere.

[0005]

The present invention has been made by paying attention to the above-mentioned conventional problems. The present inventors have found that the catalyst coating layer contains activated alumina, cerium and zirconium, and platinum and rhodium or palladium. A monolith-type exhaust gas purifying catalyst comprising a cerium- and zirconium-supporting alumina powder obtained through a precipitation-forming reaction from a suspension containing a water-soluble cerium salt, a water-soluble zirconium salt, and activated alumina powder, The metal atoms constituting the supported alumina powder are cerium 5 to 1 with respect to aluminum 100 (metal atom ratio).
The ratio of 5, zirconium 1 to 4, and the above object can be achieved by using the cerium and zirconium-supported alumina powder as a catalyst for exhaust gas purification in which platinum or palladium is supported and then a catalyst coat layer is formed. I found a thing.

[0006]

The method for producing a catalyst for purifying exhaust gas of the present invention is configured as described above to sufficiently combine both oxides of cerium and zirconium supported on alumina to improve the oxygen storage capacity of ceria by adding zirconium. The effect is obtained. As a result, under severe conditions such as a high temperature atmosphere, an exhaust gas purifying catalyst having high purifying performance even in a state before endurance and a state after endurance can be obtained.

[0007]

EXAMPLES The method for producing an exhaust gas purifying catalyst of the present invention will be described in more detail below. The cerium- and zirconium-supported alumina powder used in the present invention is, for example, a suspension prepared by mixing activated alumina powder with an acidic solution containing both cerium and zirconium ions, such as a mixed aqueous solution of cerium nitrate and zircosol acetate, to which ammonia water is added. It can be adjusted by heating and pressurizing as required, and drying and calcining the precipitate obtained here.

The composition of the cerium- and zirconium-supported alumina powder used in the present invention is preferably such that the metal atomic ratio is cerium 5 to 15 and zirconium 1 to 4 with respect to 100 of aluminum. In this range, since both cerium and zirconium oxides are combined, the effect of improving the oxygen storage capacity of ceria by the addition of zirconium appears, and sufficient improvement of the catalytic performance is recognized. However, if the metal atom ratio of zirconium to aluminum is below this range, the oxygen storage capacity of the cerium oxide cannot be sufficiently improved. Further, when the atomic ratio of cerium and zirconium exceeds the above range, it is excessively supported on the micropores and macropores of the activated alumina, and even on the surface, and the pore structure is blocked, and the surface area is reduced, thereby sufficiently improving the catalytic performance. Disappear.

As a method for producing the catalyst of the present invention, one method is to prepare a slurry by preliminarily supporting a noble metal on the cerium- and zirconium-supporting alumina powder, and apply the slurry to a ceramic or metal monolith carrier. There is a method of obtaining the target catalyst by drying and firing the monolithic carrier and then applying a slurry containing a noble metal such as platinum, rhodium and palladium, and drying and firing. Further, as another manufacturing method, an alumina powder carrying a noble metal in advance and the alumina powder carrying cerium and zirconium are wet mixed to prepare a slurry, which is applied to a ceramic or metal monolith carrier and dried. , There is a method of firing.

In any of these catalyst manufacturing processes,
By including the step of adding the cerium and zirconium-supported alumina powder produced by the precipitation reaction to the slurry used, the obtained catalyst is superior to the catalyst produced by the conventional mixed addition or impregnation addition. It has exhaust gas purification performance.

The cerium and zirconium-supported alumina powder used in the present invention can obtain a sufficient catalytic activity improving effect only with cerium and zirconium as the metal species contained therein. However, cerium is the main component of the cerium source, and other rare earth elements are used. A low-purity cerium salt containing simultaneously (for example, lanthanum, neodymium, praseodymium, yttrium) may be used. Further, it was confirmed by X-ray diffraction that the cerium and zirconium-supported alumina powder had a higher surface area than that produced by the conventional impregnation method, and that active alumina, cerium and zirconium were present in a composite form. Was done. Therefore, platinum or palladium supported on the oxide exists in a highly dispersed state,
Further, it is possible to sufficiently receive the cocatalyst effect exerted by the composite oxide of cerium and zirconium which has been conventionally known empirically.

The exhaust gas-purifying catalyst produced by the present invention is characterized by containing platinum or palladium as a noble metal component, but in order to further improve the performance, a noble metal such as rhodium may be added if necessary. May be.

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 In this example, an oxide powder containing cerium and zirconium in alumina was prepared by a coprecipitation method, and platinum was supported on the powder to catalyze. A mixed aqueous solution of cerium nitrate and zirconol acetate (cerium concentration: 1.3 moL / L, zirconium concentration: 0.2 moL / L) was prepared, and commercially available activated alumina powder (BET specific surface area 1
80 m ² / g) 750 g was gradually added, and then 1.0 to
A 3.0 N aqueous ammonia solution was gradually added to the solution,
H was adjusted to 9.0, and the mixture was stirred for about 1 hour. Then, the formed hydroxide precipitate is suction filtered, and the precipitate is dried at 150 ° C. for about 3 hours and calcined at 600 ° C. for about 1 hour to form an oxide powder containing cerium and zirconium in alumina (powder-1).
Was obtained (cerium 7.98 mol%, zirconium 1.
24 moL%, BET specific surface area = 148 m ² / g). While stirring the obtained oxide powder, a dinitrodisiamine platinum nitric acid solution (45.5 g / kg) was sprayed,
After being dried at 0 ° C. for about 3 hours, it was baked at 400 ° C. for about 1 hour to obtain a platinum-supported oxidized powder having a platinum-supported amount of 1.0% by weight. 990 g of this oxidized powder and 810 g of a 10% aqueous acetic acid solution were put into a magnetic ball mill, mixed and pulverized to prepare a slurry,
This slurry is applied to a cordierite monolith carrier 12
0 g / L was applied, dried and then baked at 400 ° C. for about 1 hour.

Further, activated alumina powder having 3% by weight of cerium loaded thereon and thermally stabilized (BET specific surface area 180 m ² /
g) with stirring, rhodium nitrate solution (44.5 g / k
g) was sprayed, dried at 150 ° C. for about 3 hours, and then calcined at 400 ° C. for about 1 hour to obtain a rhodium-supported alumina powder having a rhodium-supported amount of 1.0 wt%.

285 g of the above rhodium-supported alumina powder,
Commercially available activated alumina powder (BET specific surface area 180 m ² /
g) 510 g, and nitric acid-acidified alumina sol 1005 g
(A sol obtained by adding 10% by weight nitric acid to a 10% by weight boehmite alumina turbid solution) was put into a magnetic ball mill, mixed and pulverized to prepare a slurry, and 60 g of the slurry was applied to the carrier of the coat. / L was applied, dried and then baked at 400 ° C. for about 1 hour to obtain a catalyst-1.

Comparative Example 1 In this example, an oxide powder containing cerium and zirconium in alumina prepared by an impregnation method was supported by platinum to be catalyzed. While stirring the same mixed aqueous solution of cerium nitrate and zircosol acetate as in Example 1 at room temperature, the same activated alumina powder as in Example 1 was added, and the mixture was stirred for about 1 hour and then at 150 ° C. for about 3 hours. Dry, about 1 at 600 ℃
An oxide powder (powder-2) containing cerium and zirconium in alumina was obtained by firing for a time (the cerium and zirconium contents were the same as in Example 1, and the BET specific surface area 142).
m ² / g). A catalyst-2 was obtained in the same manner as in Example 1 except that the oxide powder obtained by the above impregnation method was used.

Comparative Example 2 In this example, an oxide powder containing cerium and zirconium in alumina was prepared by a spraying method, and platinum was supported on the powder to catalyze it. While stirring the same activated alumina powder as in Example 1, the same mixed aqueous solution of cerium nitrate and zircosol acetate as in Example 1 was sprayed, dried at 150 ° C. for about 3 hours, and then calcined at 600 ° C. for about 1 hour. Was repeated about 4 times to obtain an oxide powder (powder-3) containing cerium and zirconium in alumina (the cerium and zirconium contents are the same as in Example 1, BET specific surface area 124 m).
² / g). A catalyst-3 was obtained in the same manner as in Example 1 except that the oxide powder prepared by the above spraying method was used.

Comparative Example 3 This example is a catalyst obtained in the same manner as Comparative Example 2 except that an oxide powder containing only cerium in alumina was prepared. An oxide powder containing only cerium in alumina (powder) was prepared in the same manner as in Comparative Example 2 except that an aqueous cerium nitrate solution (cerium concentration 1.4 moL / L) was sprayed while stirring the same activated alumina powder as in Example 1. -4) was obtained (cerium content 8.6 mol%, BET specific surface area 119 m ² /
g). A catalyst-4 was obtained in the same manner as in Example 1 except that the oxide powder prepared by the above spraying method was used. Example 2 This example is a catalyst obtained in the same manner as in Example 1 except that palladium was supported instead of platinum and rhodium. The cerium concentration of the mixed aqueous solution of cerium nitrate and zircosol acetate was 1.6 moL / L and the zirconium concentration was 0.4 m.
oL / L, the composition of which is cerium 10.4 mol%,
Zirconium 2.6 mol% and BET specific surface area 1
An oxide powder containing cerium and zirconium in alumina was obtained in the same manner as in Example 1 except that the amount was 80 m ² / g.
An aqueous palladium nitrate solution (75 to 85 g / kg) was sprayed on the obtained oxide powder while stirring, dried at 150 ° C. for about 3 hours, and then calcined at 400 ° C. for about 1 hour to carry a palladium loading of 1.0 wt. % Palladium-supported oxide powder was obtained. A slurry was prepared and coated with 990 g of the above palladium-supported oxide powder in the same manner as in Example 1 to obtain Catalyst-5.

Comparative Example 4 In this example, an oxide powder containing cerium and zirconium in alumina (composition) was prepared in the same manner as in Comparative Example 1 except that a mixed aqueous solution of cerium nitrate and zircosol acetate having the same composition as in Example 2 was used. Is the same as in Example 2, BET specific surface area: 156
m ² / g) was adjusted and a catalyst-6 was obtained in the same manner as in Example 2 except that the oxide powder obtained by this impregnation method was used.

Comparative Example 5 In this example, an oxide powder containing cerium and zirconium in alumina (composition) was prepared in the same manner as in Comparative Example 2 except that a mixed aqueous solution of cerium nitrate and zircosol acetate having the same composition as in Example 2 was used. Is the same as in Example 2, BET specific surface area: 160 m
² / g) was adjusted and a catalyst-7 was obtained in the same manner as in Example 2 except that the oxide powder obtained by this spraying method was used.

Test Example 1 Catalysts 1 to 4 obtained in Example 1 and Comparative Examples 1 to 3 were
Fig. 1 shows the results of measuring the HC, CO, and NO _x purification rates of the endurance deteriorated catalyst by mounting them on an engine and subjecting them to deterioration under the catalyst endurance conditions shown below for performance evaluation under the catalyst evaluation conditions. Show.

Engine Durability Conditions (Catalyst Durability Conditions) Durability engine: Model Y44 manufactured by Nissan Motor Co., Ltd. (displacement 4000 cc, V type 8 cylinders) Operating conditions: The rotation speed was controlled so as to satisfy the following conditions. Catalyst inlet temperature 850 ° C Space velocity About 60000H ^-1 Catalyst inlet gas composition HC 1100ppm CO 0.5% NO 1300ppm O ₂ About 0.5% CO ₂ Approximately 15% Average air-fuel ratio 14.6 Durability 50 hours (Catalyst evaluation conditions) Evaluation engine: Nissan Motor Co., Ltd. RB20E type (displacement 2000cc, in-line 6 cylinders) Operating conditions: Rotate to meet the following conditions Controlled the number. Catalyst inlet temperature 400 ° C Space velocity About 60000H ^-1 Catalyst inlet gas composition HC 2200ppm CO 1.68% NO 1600ppm O ₂ About 1.3% CO ₂ 13% Average air-fuel ratio 14.6 Air-fuel ratio amplitude ± 1.0 Test example 2 For each of the catalysts 5 to 7 obtained in Example 2 and Comparative Examples 4 to 5, as in Test Example 1 except that the catalyst inlet temperature under durability conditions was 750 ° C and the catalyst inlet temperature under evaluation conditions was 480 ° C. FIG. 1 shows the results of the catalyst performance evaluation, in which the performance was evaluated after the engine was subjected to durability under the same conditions, and the HC, CO, and NO _x purification rates of the durability deteriorated catalyst were measured.

Test Example 3 FIG. 2 shows the measurement results of the BET specific surface area of the catalysts 1 to 4 of the present invention before and after the durability test (1000 ° C. × 4 hours). As described above, the surface area of the cerium- and zirconium-supported alumina powder produced by the precipitation formation reaction is 148 to 186 m ² / g before the endurance.
It is 94 to 97 m ² / g after endurance, and it is recognized that it has a clearly high surface area in both the state before endurance and the state after endurance as compared with the conventional manufacturing method. Further, it has been confirmed that the specific surface area is almost the same in the metal atomic ratio of 100 to 100 of cerium and 5 to 15 of zirconium. By supporting a noble metal on the cerium- and zirconium-supporting alumina powder having a high specific surface area, a catalyst performance higher than that of the conventional catalyst was obtained.

[0024]

As described above, the present invention is
A monolith type exhaust gas purifying catalyst whose catalyst coat layer is composed of platinum containing active alumina, cerium and zirconium, and rhodium or palladium, and precipitates are produced from a suspension containing a water-soluble cerium salt, a water-soluble zirconium salt and active alumina powder. Alumina powder supporting cerium and zirconium obtained through the reaction is included, and the metal atoms constituting the alumina powder supporting cerium and zirconium are cerium 5 to 15 and zirconium 1 to 4 relative to aluminum 100, and the cerium and zirconium supporting alumina. Since the purification catalyst for exhaust gas is characterized by forming the catalyst coating layer after supporting platinum or palladium on the powder, the exhaust gas purification after high temperature endurance is higher than that of the conventional production method, that is, the impregnation method and the spray method. Clear in performance The catalyst is obtained.

[Brief description of drawings]

FIG. 1 Structure of catalyst supporting layer and HC and C of durability deterioration catalyst
O, NO _x conversion rate measurement results

FIG. 2 Results of BET specific surface area measurement before and after endurance

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Okada 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A monolith-type exhaust gas purifying catalyst, wherein the catalyst coating layer contains activated alumina, cerium and zirconium, and is composed of platinum and rhodium or palladium. A suspension containing a water-soluble cerium salt, a water-soluble zirconium salt and activated alumina powder. A cerium- and zirconium-supporting alumina powder obtained from a liquid through a precipitation-forming reaction is contained, and the metal atoms constituting the cerium- and zirconium-supporting alumina powder are cerium 5-15 and zirconium 1-4 with respect to 100 aluminum, and A method for producing an exhaust gas purifying catalyst, comprising forming a catalyst coat layer after supporting platinum or palladium on cerium- and zirconium-supporting alumina powder.