JPS62282641A - Production of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain the title catalyst having excellent purification performance, durability, etc., by depositing a slurry contg. zirconium oxide contg. rhodium, activated alumina contg. cerium, cerium oxide, and an alumina sol on a carrier, drying and baking the obtained material, and then depositing platinum on the material. CONSTITUTION:About 0.15-7wt% rhodium is incorporated into zirconium oxide by impregnation, etc., and about 1-5wt% cerium is incorporated into activated alumina. The zirconium oxide and the activated alumina are crushed and mixed in an alumina sol to obtain a slurry, and a carrier is impregnated with the slurry, dried, and baked to form composite oxide coated film contg. rhodium on the carrier. Pt is then deposited on the coated film to obtain the catalyst. The catalyst has excellent purification performance, heat resistance, durability, etc., and is appropriately used as the catalyst for removing carbon monoxide, hydrocarbons, and nitrogen oxides in the exhaust gas from an automobile, etc.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) This invention is directed to the treatment of exhaust gases, particularly carbon monoxide (CO) and hydrocarbons (HC) in exhaust gases from internal combustion engines such as automobiles. The present invention also relates to a method for producing an exhaust gas purifying catalyst used to purify nitrogen oxides (NOX).

(Prior Art) As a conventional exhaust gas purifying catalyst, for example, there is one in which an activated alumina layer is provided on the surface of a monolithic structure carrier, and then a catalytic metal is supported thereon to form a catalyst. Such a catalyst is prepared, for example, by immersing a carrier in a slurry of 40 to 45% by weight of activated alumina containing 10% ceria (CeO After calcining at 500 °C in an air atmosphere, the carrier is then immersed in a nickel nitrate solution and dried at 125 °C, then calcined at 500 °C in an air atmosphere, and then containing chloroplatinic acid and rhodium chloride. After immersion in a solution and subsequent passage through hydrogen sulfide, the resulting support is washed with water, then dried at 125°C and then calcined in an air atmosphere at 500°C to be catalyzed.

Note that other base metal salts are also used in the nickel nitrate impregnation step. According to another method, cerium nitrate, activated alumina, and nitric acid are mixed to form a slurry without using ceria, and the slurry is coated on an integral structure carrier, dried at 125°C, and then fired in an air atmosphere at 500°C. A catalyst is formed in a similar manner using cerium nitrate as ceria.

(Problems to be Solved by the Invention) However, such conventional exhaust gas purification catalysts are coated with an activated alumina layer on which catalyst metal is supported, which is formed as described above. The metal was present near the surface of the activated alumina layer, and the activated alumina layer had insufficient heat resistance.
When traveling over long distances, there is a problem in that the active points of the catalyst are covered by the accumulation of poisonous substances, or the surface area decreases due to changes in the crystal structure of the alumina layer, causing the catalyst to lose its activity.

(Means for Solving the Problems) This invention was made by focusing on such conventional problems, and consists of zirconium oxide pre-contained with rhodium, activated alumina pre-contained cerium, and cerium oxide. The oxide and alumina sol are mixed and pulverized to form a slurry, this slurry is attached to a carrier, dried, and fired, and platinum is supported on the rhodium-containing composite oxide or mixed oxide formed on the carrier. This solves the problem.

(Function) In the method for producing an exhaust gas purification catalyst of the present invention, zirconium oxide containing rhodium in advance, activated alumina containing cerium in advance, cerium oxide, and alumina sol are mixed and pulverized to form a slurry. The slurry is impregnated into a carrier, dried, and fired. As a result, an oxide film made of a complex oxide or mixed oxide containing rhodium is formed on the carrier. Next, platinum is supported on this oxide film. The catalyst formed in this way does not deteriorate in purification performance even if the supported amount of the main catalyst metals of platinum and rhodium is reduced, and has high heat resistance and sufficient durability when used in automobiles. be.

When making a slurry by mixing and pulverizing zirconium oxide containing rhodium in advance, activated alumina containing cerium in advance, cerium oxide, and alumina sol, the amount of rhodium contained in zirconium oxide is determined in terms of metal. 0.15 to zirconium oxide
The amount of cerium contained in the activated alumina is preferably 1 to 5% by weight based on the alumina, and the amount of cerium oxide is preferably 5 to 40% by weight. If the amount of rhodium contained in the zirconium oxide exceeds 7% by weight of rhodium, the performance deteriorates, probably due to poor dispersibility, and if it is less than 0.15% by weight, the effect will hardly change. Even if the amount of cerium contained in activated alumina exceeds 5% by weight as cerium (metal equivalent) and the amount of cerium oxide powder added exceeds 40% by weight, there is almost no effect of increasing the amount of cerium; on the contrary, if activated alumina contains cerium If the amount is less than 1% by weight (metal equivalent) and if the amount of cerium oxide powder added is less than 5% by weight, the effects of their addition will be insufficient to meet the performance required by the inventors, and this is not preferred. Further, the amount of platinum supported on the oxide film made of a complex oxide or mixed oxide containing rhodium on the support is not particularly limited, but from the viewpoint of cost, it is practically limited to about 0.5% by weight. Preferably 0.15
Approximately % by weight.

(Examples) The present invention will be explained below with reference to Examples, Comparative Examples, and Test Examples.

Example 1 Zirconium oxide powder was impregnated in an aqueous rhodium chloride solution, dried and calcined in air at 600°C for 2 hours to obtain zirconium oxide powder containing 0.25% by weight of rhodium based on gorconium oxide in terms of metal. Next, alumina powder containing gamma alumina as a main component was impregnated in an aqueous cerium nitrate solution, dried, and calcined in air at 600° C. for 2 hours to obtain a carrier containing 3% by weight of cerium oxide based on alumina in terms of metal.

Next, 2478 g of alumina sol (a sol obtained by adding 10 wt% HNO to a 10 wt% suspension of boehmite alumina), 330 g of the above-mentioned rhodium-containing zirconium oxide powder, and activated alumina powder containing ceria 5
Mix 73g and 619g of ceria powder in a ball mill,
It was ground for 6 hours at Qrpm. A monolithic carrier base material (0, 0,
The process of immersing a 9f 300 cell/in'), air blowing and drying was repeated three times, an oxide coating layer was attached, and baking was performed in an air atmosphere at 650° C. for 2 hours. At this time, the amount of rhodium deposited was 0.10 g/piece, and the total amount of deposited alumina, cerium oxide, and zirconium oxide was 225 g/piece.

Further, the carrier to which rhodium, alumina, cerium oxide, and zirconium oxide were attached was immersed in an aqueous solution of chloroplatinic acid to support the platinum in an amount of 1.01 g/piece, and then heated at 600°C in an air atmosphere. Calcining was performed for 2 hours, and Catalyst 1 was obtained.

Example 2 In Example 1, 110 g of zirconium oxide powder containing 0.74% by weight of rhodium in terms of metal, and activated alumina powder containing cerium (3% by weight in terms of cerium metal) 793
A catalyst was prepared in the same manner except that 2,478 g of alumina sol, and 619 g of ceria powder were used to obtain Catalyst 2.

Example 3 In Example 1, rhodium was 1.5% by weight in terms of metal.
55g of zirconium oxide powder containing 848g of activated alumina powder containing cerium (3% by weight in terms of cerium metal)
A catalyst was prepared in the same manner except that 2478 g of alumina sol and 619 g of ceria powder were used to obtain Catalyst 3.

Example 4 In Example 1, rhodium was 1.8% by weight in terms of metal.
44 g of zirconium oxide powder containing 1 859 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal)
A catalyst was prepared in the same manner except that 2478 g of alumina sol and 619 g of ceria powder were used to obtain Catalyst 4.

Example 5 In Example 1, rhodium was 2.4% by weight in terms of metal.
33g of zirconium oxide powder containing 870g of activated alumina powder containing cerium (3% by weight in terms of cerium metal)
A catalyst was prepared in the same manner except that 2478 g of alumina sol and 619 g of ceria powder were used to obtain Catalyst 5.

Example 6 In Example 1, rhodium was 3.6% by weight in terms of metal.
22 g of zirconium oxide powder containing 1 881 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal),
A catalyst was prepared in the same manner except that 2478 g of alumina sol and 619 g of ceria powder were used to obtain catalyst 6.

Example 7 In Example 1, rhodium was 6.9% by weight in terms of metal.
11g of zirconium oxide powder, activated alumina powder containing cerium (3% by weight in terms of cerium metal) 892
A catalyst was prepared in the same manner except that 247 g of alumina sol and 619 g of ceria powder were used to obtain Catalyst 7.

Example 8 In Example 1, 550 g of zirconium oxide powder containing 0.15% by weight of rhodium in terms of metal, activated alumina powder containing cerium (3% by weight in terms of cerium metal) 3
53g, alumina sol 2478g, ceria powder 619g
A catalyst was prepared in the same manner except that catalyst 8 was obtained.

Example 9 In Example 1, 770 g of zirconium oxide powder containing 0.11% by weight of rhodium in terms of metal, and activated alumina powder containing cerium (3% by weight in terms of cerium metal) 13
A catalyst was prepared in the same manner except that 3 g of alumina sol, 2478 g of alumina sol, and 619 g of ceria powder were used to obtain catalyst 9.

Example 10 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium, 1048 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal),
A catalyst was prepared in the same manner except that 8 g of alumina sol 24T and 144 g of ceria powder were used to obtain catalyst 10.

Example 11 In Example 1, except that 330 g of zirconium oxide powder containing 0.25% by weight of rhodium, 842 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal), 2478 g of alumina sol, and 350 g of ceria powder were used. A catalyst was prepared in a similar manner to obtain catalyst 11.

Example 12 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium and 616 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal) were used.

A catalyst was prepared in the same manner except that 2563 g of alumina sol and 491 g of ceria powder were used to obtain catalyst 12.

Example 13 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium and 928 g of activated alumina powder containing cerium (1% by weight in terms of cerium metal) were used.

A catalyst was prepared in the same manner except that 2648 g of alumina sol and 94 g of ceria powder were used to obtain catalyst 13.

Example 14 Same as Example 1 except that 330g of zirconium oxide powder containing 0.25% by weight of rhodium, 367g of activated alumina powder containing cerium (1% by weight in terms of cerium metal), 2478g of alumina sol, and 826g of ceria powder were used. A catalyst was prepared by the method described above to obtain catalyst 14.

Example 15 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium and 517 g of activated alumina powder containing cerium (5% by weight in terms of cerium metal) were used.

A catalyst was prepared in the same manner except that 2563 g of alumina sol and 590 g of ceria powder were used to obtain catalyst 15.

Example 16 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium, and 321 g of activated alumina powder containing cerium (5% by weight in terms of cerium metal).

A catalyst was prepared in the same manner except that 2563 g of alumina sol and 786 g of ceria powder were used to obtain catalyst 16.

Example 17 In Example 1, 330 g of zirconium oxide powder containing 0.25% by weight of rhodium and 263 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal) were used.

A catalyst was prepared in the same manner except that 2478 g of alumina sol and 929 g of ceria powder were used to obtain catalyst 17.

Comparative Example 1 2,648 g of alumina sol (a sol obtained by adding 10% by weight of HNO3 to a 10% by weight suspension of boehmite alumina) and 1,352 g of activated alumina powder were mixed in a ball mill and pulverized at 8 Q rpm for 6 hours. A monolithic carrier base material (0.9f 300 cells/1n2) is immersed in this alumina-containing solution (coating solution), air-blown and then dried three times to adhere an alumina coating layer, and then air heated to 650°C Firing was performed in an atmosphere for 2 hours. The amount of alumina deposited at this time was set at 225 g/piece.

Further, this carrier with alumina attached was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and the amount of platinum and rhodium attached was 1.01 g/piece of platinum and 0.0 g/piece of rhodium. l.

After supporting 87 pieces, calcination was performed in an air atmosphere at 600°C for 2 hours to obtain catalyst A.

Comparative Example 2 A catalyst was prepared in the same manner as in Comparative Example 1, except that 590 g of ceria powder was added in addition to 2563 g of alumina sol and 847 g of activated alumina powder, and 1 fathom of catalyst B was used.

Comparative Example 3 In Comparative Example 1, activated alumina powder containing cerium (
A catalyst was prepared in the same manner, except that 1352 g of cerium (3% by weight calculated as metal) and 2648 g of alumina sol were used to obtain Catalyst C.

Comparative Example 4 In Example 1, rhodium was 8.5% by weight in terms of metal.
9 g of zirconium oxide powder containing 1 894 g of activated alumina powder containing cerium (3% by weight in terms of cerium metal)
A catalyst was prepared in the same manner except that 247 g of alumina sol and 619 g of ceria powder were used.

Test Examples Catalysts 1 to 17 obtained in Examples 1 to 17 and catalysts A to D obtained in Comparative Examples 1 to 4 were subjected to engine durability under the following conditions, and the purification rate of 10 mode emission by vehicle was measured. Table 1 shows the purification rate as 5=.

Engine durability conditions Catalyst Integrated noble metal catalyst Catalyst outlet temperature
Approximately 750℃ Space velocity Approximately 70,800r' Endurance time 100 hours Engine displacement 2.200cc Vehicle evaluation conditions Engine displacement 1800cc 10%
-Dobase Emissi 97 HC1.5~1.8g/k
mCO5, 0 to 6.0 g/km No. 0.9 to 1.0 g/km (Effect of the invention) As explained above, according to this invention, zirconium oxide containing rhodium in advance and cerium in advance are The activated alumina, cerium oxide, and alumina are mixed and ground to form a slurry, and this slurry is impregnated into a carrier, dried, and fired to form a rhodium-containing complex oxide or mixed oxide formed on the carrier. Due to the structure supporting platinum, the resulting catalyst has a significantly improved exhaust gas purification rate and improved durability, which has the effect of being able to show a high purification rate even with a low amount of main catalyst metal. can get.

Claims (1)

[Claims] 1. Mix and grind zirconium oxide pre-contained with rhodium, activated alumina pre-contained cerium, cerium oxide, and alumina sol to form a slurry, adhere this slurry to a carrier, dry it, sinter it, and apply it on the carrier. A method for producing an exhaust gas purifying catalyst for removing carbon monoxide, hydrocarbons, and nitrogen oxides from exhaust gas, characterized by supporting platinum on the formed rhodium-containing composite oxide or mixed oxide film. .