JPH0361492B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical field to which the invention relates) This invention simultaneously eliminates nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) in exhaust gases emitted from internal combustion engines of vehicles, particularly automobile internal combustion engines. The present invention relates to a method of manufacturing a catalyst for purifying exhaust gas that efficiently reduces exhaust gas. (Prior art) After adhering activated alumina powder containing cerium to the surface of a monolithic carrier base material,
Catalysts in which platinum, rhodium, palladium, etc. are supported either singly or in combination have been proposed, for example, in JP-A-52-116779 and JP-A-54-159391. However, in the case of such conventional exhaust gas purification catalysts, expensive platinum, which is a catalyst component,
Although a large amount of noble metals such as rhodium and palladium were supported on activated alumina, the noble metal was supported on the activated alumina after a large amount of cerium was supported on it, so the resulting catalyst had a poor dispersion state of the precious metal. Therefore, there was a problem that the activity, especially in the low temperature range, decreased. (Disclosure of the Invention) This invention was made by focusing on such conventional problems, and consists of activated alumina powder containing cerium in advance and cerium oxide powder having a specific surface area of 50 m ² /g or more. After adhering the slurry obtained by blending with alumina sol to the surface of the monolith carrier base material, the precious metal component consisting of platinum and rhodium or palladium and rhodium is supported, preventing deterioration of the dispersion state of the precious metal, and at the same time reducing exhaust gas. The purpose of the present invention is to provide a method for producing a catalyst for exhaust gas purification in which precious metal content is reduced by increasing the oxygen (O ₂ ) storage effect of ceria in order to improve the purification performance of ceria. In general, activated alumina such as γ-alumina and δ-alumina transforms into a stable inert alumina called α-alumina at high temperatures, with a specific surface area of 1 to 2 m ² /
It will only have g. Therefore, if an activated alumina carrier is used as it is as a catalyst carrier and a noble metal such as platinum or rhodium is supported on it to form a catalyst, when exposed to high temperatures, the supported noble metal will sinter and lose its activity. lose. However, when cerium oxide is supported on activated alumina as in the case of the catalyst of the present invention, the heat resistance of activated alumina is significantly improved, and it becomes difficult to convert into α-alumina even when used at high temperatures. The amount of cerium oxide supported on activated alumina is 1 to 5% by weight relative to alumina in terms of cerium metal, and is 1% by weight.
If it is less than 5% by weight, the effect of improving the heat resistance of activated alumina will be small, and if it exceeds 5% by weight, the heat resistance will be improved, but the specific surface area of activated alumina will be relatively reduced, which is not preferable. In this invention, in order to fully take these effects into consideration and further increase the O ₂ storage effect of cerium oxide, activated alumina powder containing cerium oxide in advance has a specific surface area of 50 m ² /g or more. After adhering a slurry obtained by blending cerium oxide (hereinafter referred to as high specific surface area ceria) powder to the surface of a monolithic carrier base material,
Supports precious metal components. This noble metal component is supported by a commonly used method. The high specific surface area ceria used here is, for example, ceria with a specific surface area of 50 m ² /g or more obtained by baking cerous nitrate and cerium acetate among various cerium salts at 650°C for 1 hour in an air atmosphere. can be,
Ceria obtained from cerous nitrate is 50.8 m ² /
g, ceria obtained from cerium acetate is 60.0 m ² /
It has a specific surface area of g. For example, ceria obtained by firing other cerium salts under the same conditions is 17.9 m ² /g from cerium carbonate, and 19.6 m ² /g from cerium oxalate.
Ceria, which has a low specific surface area of less than 50 m ² /g, has a specific surface area of 6 m ² /g.
Since the improvement in performance could not meet the inventors' requirements compared to the case where a commercially available ceria of about 50% is used, ceria having a specific surface area of 50 m ² /g or more is used. As a result, the catalyst has ceria, which has a specific surface area almost equal to that of activated alumina, and its exhaust gas purification performance does not deteriorate even if the amount of precious metal supported is reduced, and it also has excellent durability when used for purifying automobile exhaust gas. was also sufficient. In particular, the O ₂ storage capacity of Ceria, which has a high specific surface area, has _a large effect on improving the purification ability. As a result of increased effectiveness,
It shows stable and high purification performance. The amount of high specific surface area ceria powder to be blended with activated alumina powder is 5 to 50% by weight based on the alumina layer attached to the monolith carrier base material in terms of metal.
If it exceeds 50% by weight, there is almost no effect of increasing the amount, and if it is less than 5% by weight, the effect of adding ceria with a high specific surface area is insufficient compared to the performance required by the inventor. (Examples of the Invention) The present invention will be explained using the following Examples, Comparative Examples, and Test Examples. Example 1 A granular carrier (particle size 2 to 4 mm) mainly composed of gamma alumina was impregnated with an aqueous cerium nitrate solution, dried, and then calcined in an air atmosphere at 600°C for 1 hour to convert cerium oxide to alumina as a metal. Converted 1% by weight
A carrier containing the above was obtained. Next, 2478.0 g of alumina sol (a sol obtained by adding 10 wt.% _NHO3 to a 10 wt.% suspension of boehmite alumina), 1419 g of activated alumina granular carrier containing cerium, and ceric nitrate were prepared. After 103.2 g of high specific surface area ceria powder was put into a ball mill pot and pulverized for 6 hours, the resulting slurry was adhered to a monolithic carrier base material (1.7400 cells), dried, and then calcined at 650° C. for 2 hours. The amount of adhesion layer deposited at this time was set at 340 g/piece. Furthermore, this carrier has 0.77 platinum per carrier.
After supporting the catalyst in amounts of 0.13 g and 0.13 g of rhodium, catalyst 1 was obtained by calcining (600°C x 2 hours). Example 2 The same procedure as in Example 1 was carried out, except that a granular carrier containing gamma alumina as the main component was impregnated with an aqueous cerium nitrate solution, dried, and calcined to obtain a carrier containing 3% by weight of cerium oxide based on alumina in terms of metal. Catalyst 2 was obtained. Example 3 Catalyst 3 was obtained in the same manner as in Example 1, except that 903 g of activated alumina granular carrier containing cerium and 619 g of high specific surface area ceria powder were used. Example 4 In Example 1, 491 g of activated alumina granular carrier containing cerium and 1032 g of high specific surface area ceria powder
Catalyst 4 was obtained in the same manner except that . Example 5 In Example 2, 1007 g of activated alumina granular carrier containing cerium and 516 g of high specific surface area ceria powder were used.
Catalyst 5 was obtained in the same manner except that . Example 6 In Example 2, 491 g of activated alumina granular carrier containing cerium and 1032 g of high specific surface area ceria powder
Catalyst 6 was obtained in the same manner except that . Example 7 The same procedure as in Example 1 was carried out, except that a granular carrier containing gamma alumina as the main component was impregnated with an aqueous cerium nitrate solution, dried, and calcined to obtain a carrier containing 5% by weight of cerium oxide in terms of metal based on the alumina. Catalyst 7 was obtained. Example 8 In Example 7, 1007 g of activated alumina granular carrier containing cerium, 516 g of high specific surface area ceria powder
Catalyst 8 was obtained in the same manner except that . Example 9 In Example 7, 491 g of activated alumina granular carrier containing cerium, 1032 g of high specific surface area ceria powder
Catalyst 9 was obtained in the same manner except that . Comparative Example 1 Alumina sol 2563.0g, activated alumina granular carrier
1437.0g was mixed in a ball mill and pulverized for 6 hours, then adhered to a coating carrier base material (1.7400 cells) and fired (650°C x 2 hours). The amount of adhesion at this time was set at 340 g/piece. Furthermore, this carrier was immersed in an acidic solution of platinum and rhodium in hydrochloric acid, and 1.9 g/kg of platinum and 0.19 g/kg of rhodium were added.
After supporting the catalyst in an amount of 1.5 g/kg, catalyst A was obtained by calcining at 600° C. for 2 hours. Comparative Example 2 Catalyst B was obtained in the same manner as in Comparative Example 1, except that 2563 g of alumina sol and 1437 g of activated alumina granular carrier containing 5% by weight of cerium in terms of metal were used. However, the amount of platinum deposited is 1.9g/ke, and the amount of rhodium is 0.19g/ke.
It was set to . Comparative Example 3 Catalyst C was obtained in the same manner except that 2478 g of alumina sol, 983 g of high specific surface area ceria powder (specific surface area 50 m ² /g), and 466 g of activated alumina granular carrier were used.
However, the amount of precious metal supported is 1.9g of platinum per catalyst.
Rhodium was set at 0.19g. Comparative example 4 Alumina sol 2563g, cerium equivalent to 0.5 as metal
Example 1 except that 1367.2 g of active alumina granular carrier containing % by weight and 69.8 g of high specific surface area ceria powder were used.
Catalyst D was obtained in the same manner as above. However, the amount of precious metal supported is 0.772g of platinum and 0.1286g of rhodium per catalyst.
It was set to Comparative Example 5 Catalyst E was obtained in the same manner as in Example 1, except that 2563 g of alumina sol, 31.9 g of activated alumina granular carrier containing 10% by weight of cerium as metal, and 1405 g of high specific surface area ceria powder were used. The amount of precious metal supported per catalyst was set to 0.772 g of platinum and 0.1286 g of rhodium. Example 10 Catalyst 10 was obtained in the same manner as in Example 1, except that ceria obtained from cerium acetate and having a specific surface area of 60 m ² /g was used. Example 11 In Example 1, except that the monolith carrier base material was changed from 400 cells, 1.7 to 300 cells, 0.9.
Catalyst 11 was obtained in the same manner. However, the total amount of the activated alumina containing cerium and the high specific surface area ceria alumina sol, that is, the amount of the adhesion layer, is 180 g/kg.
The amount of precious metals supported was set to 0.9535 g of platinum and 0.1589 g of rhodium per piece. Example 12 Catalyst 12 was obtained in the same manner as in Example 1 except that the monolith carrier base material was changed from 400 cells 1.7 to 300 cells 0.7. However, the amount of adhesion layer is
140g/piece, precious metal loading is 0.7865 platinum per piece
g, rhodium 0.0787 g. Example 13 Catalyst 12 was obtained in the same manner as in Example 1 except that the monolith carrier base material was changed from 400 cells 1.7 to 400 cells 1.32. However, the amount of adhesion layer is
264g/piece, precious metal loading is 0.5993 platinum per piece
g, rhodium was set at 0.0999 g. Comparative example 6 Cerium oxide compared to alumina in terms of metal 1
1,419 g of active alumina granular carrier containing % by weight, 2,478 g of alumina sol, and 103.2 g of ceria with a specific surface area of 17.9 m ² /g obtained from cerium carbonate were placed in a ball mill pot, and after pulverizing for 6 hours, the resulting slurry was Monolith carrier substrate (1.7, 400
After drying, it was baked at 650°C for 2 hours. The amount of adhesion at this time was set at 340 g/piece.
Furthermore, after supporting 0.77 g of platinum and 0.13 g of rhodium per piece on this carrier, it was fired (600 g).
℃ x 2 hours) to obtain catalyst F. Comparative Example 7 Catalyst G was obtained in the same manner as in Comparative Example 6, except that commercially available ceria having a specific surface area of 6 m ² /g was used. The amount of precious metal supported per catalyst is platinum
It was set to 0.77g and rhodium 0.13g. Comparative Example 8 Catalyst H was obtained in the same manner as in Comparative Example 1 except that the monolith carrier base material was changed from 400 cells 1.7 to 300 cells 0.9. In this case, the amount of slurry deposited after firing was 180 g/piece. However, the amount of precious metals supported is 0.9535g of platinum and 0.1589g of rhodium per unit.
It was set to g. Comparative Example 9 In this example, an example of the catalyst disclosed in JP-A-52-116779 is shown. 2,563 g of silica and 1,437 g of activated alumina granular carrier containing 3% by weight of cerium (metal equivalent) were mixed in a ball mill, pulverized for 6 hours, attached to a coating carrier base material (400 cells, 1.7), and baked at 650°C for 2 hours. . The amount of adhesion at this time was set at 340 g/piece.
Further, this coated carrier was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and reduced in a flow of H ² /N ² . The amount of precious metal supported at this time is platinum
It was set at 1.9 g/piece and rhodium at 0.19 g/piece. Thereafter, catalyst I was obtained by calcining at 600°C for 2 hours. Comparative Example 10 In this example, an example of the catalyst disclosed in JP-A-54-159391 is shown. Alumina sol 2563g, activated alumina granular carrier
After 1437 g was mixed in a ball mill and pulverized for 6 hours, it was attached to a coating carrier base material (400 cells, 1.7) and baked at 650°C for 2 hours. The amount of adhesion at this time was set at 340 g/piece. Then Ce( _NO3 ) ₃
Using an aqueous solution, 28 g of cerium was deposited in terms of cerium metal. After that, dry at 120℃ for 3 hours,
It was fired in air at 600°C for 2 hours. Furthermore, it was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and the amount of platinum and rhodium deposited on the platinum
After supporting 1.9 g of rhodium and 0.19 g of rhodium, catalyst J was obtained. Example 14 In Example 1, the amount of palladium deposited was set to 0.77.
Catalyst 14 was obtained in the same manner except that rhodium was supported at 0.13 g/piece. Example 15 In Example 5, the amount of palladium deposited was set to 0.77.
Catalyst 15 was obtained in the same manner except that rhodium was supported on 0.13 g/piece. Comparative Example 11 In Comparative Example 1, the amount of palladium deposited was 1.9
Catalyst K was obtained in the same manner except that rhodium was supported at 0.19 g/piece. Test Example 1 Catalysts 1 to 15 obtained from Examples 1 to 15, Comparative Example 1
Catalysts A to K obtained from 11 to 11 were tested for durability under the following conditions, and the purification rates of the 10-mode edition were compared and shown in Table 1. Durability test conditions Catalyst Monolithic precious metal catalyst Exhaust gas catalyst outlet temperature 750℃ (850℃Example 10 Comparative Example 6) Space velocity Approx. 70,000 Hr ^-1 (Approx. 100,000 Hr ^-1 Example 10 Comparative Example 6) Durability time 100 hour engine Displacement 2200c.c. Mid-durability inlet emission CO 0.4~0.6% O ₂ 0.5±0.1% NO 2500ppm HC 1000ppm CO ₂ 14.9±0.1% 10 mode evaluation vehicle Sedryk Displacement 2000c.c. (Nissan Motor Co., Ltd. ): Product name) (Stanza Displacement 1800c.c. Example 10 (Made by Nissan Motor Co., Ltd.: Product name) Comparative example 6)

[Table] Shows that.
Test Example 2 Catalysts 1 to 15 obtained from Examples 1 to 15, Comparative Example 1
Catalysts A to K obtained from 1 to 11 were thermally degraded in advance under the following conditions, and Z characteristics were evaluated using a laboratory evaluation device, and the HC and NO addition rates are shown in FIGS. 1 to 8. Thermal degradation test Temperature x time 750℃ x 24 hours Atmosphere Laboratory evaluation conditions in air Catalyst size Diameter 36mm x length 59mm Approx. 60c.c. Model gas flow rate 27.5/min Space velocity SV 27500Hr ^-1 Catalyst inlet gas temperature 400℃ Z value Setting Z=
Concentration of each gas determined by [O ₂ ] + 0.5 [NO] / 0.5 [CO] + [H ₂ ] + 1.5 [HC], where CO ₂ and H ₂ O are constant Conversion rate = [Inlet gas concentration] - [Catalyst outlet gas concentration] / [Inlet gas concentration] x 100 (%) Figure 1 is a comparison between catalyst A and catalysts 1, 2, and 3, and Figure 2 is a comparison between catalyst C and catalysts 4, 5, and 6. , Figure 3 is a comparison of catalyst B and catalysts 7, 8, and 9, Figure 4 is a comparison of catalysts D, E, and catalyst 1, and Figure 5 is a comparison of catalyst H and catalyst 1.
Comparison of 1, 12, and 13, Figure 6 shows catalyst K and catalyst 1.
7 shows a comparison between catalysts I and J and catalyst 5, and FIG. 8 shows a comparison between catalysts F and G and catalyst 10. From Figures 1 to 8, the catalyst of this invention is
O ₂ of cerium oxide with a specific surface area of 50 m ² /g or more has excellent Z characteristics and can obtain a high conversion rate of HC especially in the oxygen-deficient region of Z value 0.4 and 0.7.
Improvement in storage efficiency was confirmed. (Effects of the Invention) As explained above, according to the method of the present invention, the obtained catalyst is produced by mixing a slurry obtained by blending ceria with a high specific surface area with activated alumina powder that has previously contained cerium, onto a monolithic carrier. As it is made up of a material that supports precious metal components after adhering to the surface of the base material, as is clear from Table 1, the purification rate is significantly improved even though the precious metal content is reduced. The higher the ratio of high specific surface area ceria incorporated, the better the O ₂ storage effect of the ceria, the higher the NO purification rate, and the more stable and high purification performance can be obtained.

[Brief explanation of drawings]

Figures 1 to 8 are curves showing the relationship between NO and HC conversion rates and Z values for the catalysts of Examples and Comparative Examples, respectively; Figure 1 is a comparison of catalyst A and catalysts 1, 2, and 3; Figure 3 is a comparison between catalyst C and catalysts 4, 5, and 6, Figure 3 is a comparison between catalyst B and catalysts 7, 8, and 9, Figure 4 is a comparison between catalysts D, E, and catalyst 1, and Figure 5 is a comparison between catalyst H and catalysts. catalyst 1
Comparison of 1, 12, and 13, Figure 6 shows catalyst K and catalyst 1.
7 shows a comparison between catalysts I and J and catalyst 5, and FIG. 8 shows a comparison between catalysts F and G and catalyst 10.

Claims (1)

[Claims] 1 Alumina sol containing activated alumina powder containing 1 to 5% by weight of cerium oxide in terms of metal based on alumina, and a specific surface area of 5 to 50% by weight in terms of metal based on alumina of 50 m ² /g or more. In the exhaust gas of an internal combustion engine, which is characterized in that a slurry obtained by blending with cerium oxide powder is adhered to the surface of a monolithic carrier base material, and then a noble metal component consisting of platinum and rhodium or palladium and rhodium is supported. A method for producing an exhaust gas purification catalyst that efficiently reduces hydrocarbons, carbon monoxide, and nitrogen oxides.