JPH0334367B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention deals with nitrogen oxides (NOx) in exhaust gas emitted from vehicle engines, etc., especially automobile engines.
The present invention relates to a method for producing an exhaust gas purifying catalyst that efficiently reduces hydrocarbons (HC) and carbon monoxide (CO). (Conventional technology) Conventionally, the exhaust gas emitted from vehicle engines, etc.
Many catalysts have been proposed to detoxify NOx, HC and CO. For example, after adhering activated alumina powder to the surface of a monolithic carrier base material, a catalyst supported with platinum (Pt), rhodium (Rh), palladium (Pd), etc., individually or in combination, or mixed with cerium in advance. After adhering activated alumina powder to the surface of a monolithic carrier base material, a catalyst supporting Pt, Rh, Pd, etc., individually or in combination (e.g.,
14600), or a catalyst in which a mixture of activated alumina powder and zirconia powder is attached to the surface of a monolithic carrier, and then platinum, rhodium, palladium, etc. are supported individually or in combination ( Special Publication No. 47-50980). (Problems to be Solved by the Invention) However, in such conventional exhaust gas purification catalysts, in order to maintain exhaust gas purification performance, expensive precious metals such as platinum, rhodium, and palladium, which are catalyst components, are used. It is necessary to carry a large amount of metal, which causes the problem of consuming a large amount of precious metal, which is an extremely limited resource, and increasing the price per vehicle. (Means for Solving the Problems) This invention was made by focusing on the conventional problems as described above, and includes a method of forming activated alumina powder containing cerium in advance by adding cerium to activated alumina powder. A coating liquid is prepared by blending ceria powder and zirconia powder with this powder, and then this coating liquid is applied to the surface of a monolith carrier base material, and then platinum and rhodium are supported as noble metal components. The present invention relates to a method for producing an exhaust gas purifying catalyst. In the method of this invention, a coating solution formed by blending ceria powder and zirconia powder with activated alumina powder containing cerium in advance as described above is applied to the surface of a monolithic carrier base material, and then platinum and rhodium By doing this, while maintaining the exhaust gas purification performance, the oxygen storage effect of ceria is sufficiently produced, and the noble metal dispersion effect of zirconium is produced, and platinum, which is a catalyst component, is supported. Even if the amount of rhodium supported is small, the purification performance can be maintained without deterioration, and when used for automobiles, durability can be maintained sufficiently. Here, the "oxygen storage effect of ceria" refers to ceria taking in oxygen in an oxidizing atmosphere and becoming completely CeO ₂ , and releasing oxygen in a reducing atmosphere, i.e., in a fuel-excess region, forming an oxygen-deficient structure. This refers to the effect of storing oxygen. In the present invention, the amount of cerium contained in the activated alumina powder is preferably 1 to 5% by weight based on the total amount of the layer to be adhered to the monolith carrier base material in terms of metal. In addition, the amount of ceria powder and zirconia powder to be blended is 5 ceria powder to the total amount of the layer to be attached to the monolith carrier base material in terms of metal.
-50% by weight, preferably 1-10% by weight of zirconia powder. The reason for this is that if the amount of cerium contained in the activated alumina powder exceeds 5% by weight (metal equivalent), the ceria powder to be blended exceeds 50% by weight (metal equivalent), and the zirconia powder to be blended exceeds 10% by weight, the amount should be increased. There is almost no effect; on the other hand, the amount of cerium contained in the activated alumina powder is 1% by weight.
(metal equivalent), ceria powder is less than 5% by weight (metal equivalent), and zirconia powder is less than 1% by weight (metal equivalent), the addition effect is
This is insufficient compared to the performance required by the inventors. (Examples) Next, the present invention will be explained in detail using Examples, Comparative Examples, and Test Examples. Example 1 After impregnating a granular carrier (particle size 2 to 4 mm) mainly composed of gamma alumina in a cerium nitrate aqueous solution,
Dry and sinter in air at 600°C for 1 hour to add 1% by weight of cerium oxide to alumina in terms of metal.
A carrier containing the above was obtained. Next, 2560.3 g of alumina sol (sol obtained by adding 10 wt% HNO ₃ to a 10 wt% suspension of boehmite alumina), 1317.1 g of activated alumina granular carrier containing cerium, 98.3 g of commercially available ceria powder, and commercially available zirconia powder After introducing 21.6 g into a ball mill and mixing and pulverizing for 6 hours, the obtained alumina-containing liquid (hereinafter referred to as coating liquid) was applied to a monolithic carrier substrate (1.7, 400 cells), and then heated at 650°C for 2 hours.
Baked for an hour. The amount of adhesion in this case was set at 340 g/piece. The carrier base material treated in this way was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride to support the platinum and rhodium in an amount of 0.82 g of platinum and 0.082 g of rhodium, and then heated at 600°C for 2 hours. Baked,
Catalyst 1 was obtained. Example 2 In Example 1, 2563.0 g of alumina sol, 825.8 g of active alumina granular carrier containing cerium, 589.6 g of commercially available ceria powder, and 21.6 g of commercially available zirconia powder
Catalyst 2 was obtained in the same manner except that . Example 3 In Example 1, 2563.0 g of alumina sol, 432.7 g of activated alumina granular carrier containing cerium, 982.7 g of commercially available ceria powder, and 21.6 g of commercially available zirconia powder
Catalyst 3 was obtained in the same manner except that . Example 4 In Example 1, 2563.0 g of alumina sol, 880.8 g of activated alumina granular carrier containing cerium (3% by weight in terms of cerium metal), and 491.3 g of commercially available ceria powder
Catalyst 4 was obtained in the same manner except that 64.8 g of commercially available zirconia powder was used. Example 5 In Example 1, 2563.0 g of alumina sol, 880.8 g of active alumina granular carrier containing cerium, 491.3 g of commercially available ceria powder, and 64.8 g of commercially available zirconia powder
Catalyst 5 was obtained in the same manner except that g was changed. Example 6 In Example 1, 2563.0 g of alumina sol, 238.2 g of active alumina granular carrier containing cerium (10% by weight in terms of cerium metal), and 982.7 g of commercially available ceria powder
Catalyst 6 was obtained in the same manner except that 216.1 g of commercially available zirconia powder was used. Example 7 Catalyst 7 was obtained in the same manner as in Example 1, except that the immersed noble metal aqueous solution was changed to a chloroplatinic acid aqueous solution. However, the amount of platinum deposited was set at 0.82 g/piece. Example 8 Catalyst 8 was obtained in the same manner as in Example 1 except that the noble metal aqueous solution immersed was changed to chloroplatinic acid and palladium chloride. However, the amount of platinum attached is 0.82
g/piece, and the amount of palladium deposited was set to 0.082 g/piece. Comparative Example 1 Alumina sol 2563.0g and activated alumina granular carrier
1437.0g was introduced into a ball mill, mixed and pulverized for 6 hours to obtain a coating liquid, and this coating liquid was attached to a monolith carrier base material (1.7, 400 cells).
It was baked at 650°C for 2 hours. The adhesion amount in this case is 340
g/piece. The carrier base material treated in this manner was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride to support the platinum and rhodium in an amount of 1.9 g of platinum and 0.19 g of rhodium, and then heated at 600°C for 2 hours. Catalyst A was obtained by calcination. Comparative Example 2 2563.0 g of alumina sol, activated alumina granular carrier containing cerium (5% by weight in terms of cerium metal)
Catalyst B was obtained in the same manner as in Comparative Example 1 except that the amount was changed to 1437.0 g. However, the amount of platinum deposited is 1.9g/piece,
The amount of rhodium deposited was set at 0.19 g/piece. Comparative Example 3 Alumina sol 2563.0g, activated alumina granular carrier
Catalyst C was obtained in the same manner as in Comparative Example 1, except that 1220.9 g and 216.1 g of commercially available zirconia were used. However, the amount of platinum deposited is 1.9g/piece of platinum and 0.19g of rhodium.
g/piece. Comparative Example 4 Alumina sol 2563.0g, activated alumina granular carrier
1437.0g was introduced into a ball mill and mixed and ground for 6 hours to obtain a coating liquid. This coating liquid was applied to a monolith carrier substrate (1.7, 400 cells) and baked at 650°C for 2 hours. The amount of adhesion in this case was set at 340 g/piece. The carrier base material treated in this way was further immersed in a chloroplatinic acid aqueous solution to support platinum in an amount of 1.9 g, and then baked at 600°C for 12 hours.
Catalyst D was obtained. Comparative Example 5 Catalyst E was obtained in the same manner as in Comparative Example 4, except that it was immersed in a mixed aqueous solution of chloroplatinic acid and palladium chloride and supported so that the amount of platinum and palladium deposited was 1.9 g of platinum and 0.19 g of palladium. Ta. Comparative Example 6 Catalyst F was obtained in the same manner as in Comparative Example 4 except that 2563.0 g of alumina sol and 1437.0 g of activated alumina granular carrier containing cerium (5% by weight in terms of cerium metal) were used. However, the amount of platinum deposited is 1.9 platinum.
g/piece. Comparative Example 7 In Comparative Example 6, the samples were immersed in a mixed aqueous solution of chloroplatinic acid and palladium chloride, and the amounts of platinum and palladium deposited were 1.9 g/piece of platinum and 1.9 g/piece of palladium, respectively.
Catalyst G was obtained in the same manner except that it was supported at 0.19 g/piece. Comparative Example 8 Alumina sol 2563.0g, activated alumina granular carrier
1220.9 g of commercially available zirconia and 216.1 g of commercially available zirconia were introduced into a ball mill and mixed and ground for 6 hours to obtain a coating liquid. This coating liquid was applied to a monolith carrier substrate (1.7, 400 cells) and baked at 650°C for 2 hours. The amount of adhesion in this case was set at 840 g/piece. The carrier substrate thus treated was further immersed in an aqueous chloroplatinic acid solution to support platinum in an amount of 1.9 g, and then calcined at 600° C. for 2 hours to obtain catalyst H. Comparative Example 9 In Comparative Example 8, the pieces were immersed in a mixed aqueous solution of chloroplatinic acid and palladium chloride, and the amount of platinum and palladium deposited was 1.9 g of platinum and 0.19 g of palladium per piece.
Catalyst I was prepared in the same manner except that it was supported so that
I got it. Comparative Example 10 Catalyst J was obtained in the same manner as in Comparative Example 1, except that 2563.0 g of alumina sol and 454.3 g of activated alumina granular carrier containing cerium (50% by weight in terms of cerium metal) were used. However, the amount of platinum and rhodium deposited is 1.9g of platinum and 1.9g of rhodium per piece, respectively.
It was set at 0.19g. Comparative Example 11 In Comparative Example 1, 2563.0 g of alumina sol, 238.2 g of activated alumina granular carrier, and commercially available zirconia powder were used.
Catalyst K was obtained in the same manner except that 216.1 g of commercially available ceria powder was used. However, the deposited amounts of platinum and rhodium were set to 1.9 g of platinum and 0.19 g of rhodium per piece, respectively. Comparative Example 12 In Comparative Example 1, 2563.0 g of alumina sol, 454.3 g of activated alumina granular carrier containing cerium (50% by weight in terms of cerium metal), and 982.7 g of commercially available ceria powder
Catalyst L was obtained in the same manner except that the catalyst was changed to However, the deposited amounts of platinum and rhodium were set to 1.9 g of platinum and 0.19 g of rhodium per piece, respectively. Example 9 Catalyst 9 was obtained in the same manner as in Example 1, except that the noble metal aqueous solution immersed in it was changed to a mixed aqueous solution of dinitrodiamine platinum and rhodium nitrate. However, the deposited amounts of platinum and rhodium were set to 0.82 g of platinum and 0.082 g of rhodium, respectively. Example 10 2563.0 g of alumina sol, activated alumina granular carrier containing cerium (10% by weight in terms of cerium metal)
Catalyst 10 was obtained in the same manner as in Example 1, except that 31.9 g of commercially available ceria powder and 324.2 g of commercially available zirconia were used. However, the amount of platinum deposited is 0.82 platinum.
g/piece, and the adhesion amount of rhodium was set to 0.082 g/piece. Example 11 2563.0 g of alumina sol, activated alumina granular carrier containing cerium (0.5% by weight in terms of cerium metal)
Catalyst 11 was obtained in the same manner as in Example 1, except that 1367.2 g of commercially available ceria powder and 10.8 g of commercially available zirconia were used. However, the amount of platinum deposited is 0.82 platinum.
g/piece, and the amount of rhodium supported was set to 0.082 g/piece. Comparative Example 13 Catalyst M was obtained in the same manner as in Comparative Example 1, except that the noble metal aqueous solution to be immersed was changed to a mixed aqueous solution of dinitrodiaminoplatinum and rhodium nitrate. However, the adhesion amount of platinum and rhodium is 1.9 platinum each.
g, and rhodium was set at 0.19 g. Test Examples Catalysts 1-11 obtained from Examples 1-11, Comparative Examples 1-
The catalysts A to M obtained from No. 13 were tested for durability under the following conditions, and the purification rate of 10-mode emission [hydrocarbons (HC) in gas] was determined using a car equipped with a Sedrick CA-20 electronically controlled carburetor manufactured by Nissan Motor Co., Ltd. , carbon monoxide (CO), and nitrogen oxides (NO)], and the results are shown in Table 1. Durability test conditions Catalyst Monolithic precious metal catalyst Catalyst outlet temperature 750℃ Space velocity Approximately 70,000H ^-1 Durability time 100 hours Engine displacement 2200c.c. Gas composition CO 0.4-0.6% by weight O ₂ 0.4-0.6% by weight NO 2500ppm HC 1000ppm _CO2 14.8~15.0wt% _N2 balance

[Table] (Effects of the Invention) As explained above, the method for producing a catalyst of the present invention uses a coating liquid formed by blending activated alumina powder containing cerium with ceria powder and zirconia powder into a monolith. Since the catalyst metal component is supported on the surface of the carrier base material, as is clear from the results of the test example, the resulting catalyst has a higher precious metal component than the catalyst of the comparative example, even if it is small. It has the remarkable effect of maintaining exhaust gas purification performance and reducing precious metals by approximately 40%.

Claims (1)

[Claims] 1. Activated alumina powder contains cerium, the resulting cerium-containing alumina powder is blended with ceria powder and zirconia powder to create a coating liquid, and then this coating liquid is attached to the surface of a monolithic carrier base material. A method for producing an exhaust gas purifying catalyst, which comprises supporting platinum and rhodium as precious metal components. 2. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the amount of cerium contained in the activated alumina powder is 1 to 5% by weight based on the total amount of the layer to be adhered to the monolithic carrier base material in terms of metal. . 3. The amount of ceria powder and zirconia powder to be blended is 5 to 50% by weight of ceria powder and 1 to 10% by weight of zirconia powder based on the total amount of the layer to be attached to the monolithic carrier base material in metal terms. A method for producing an exhaust gas purifying catalyst according to item 1.