JPH0480736B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a method for producing a catalyst carrier for use in detoxifying hydrocarbons, carbon monoxide, and nitrogen oxides, and in particular for purification of automobile exhaust gas and stationary engine exhaust gas. The present invention relates to a method for producing a catalyst carrier used for. [Prior art] An integrated structure carrier (monolith carrier) has various materials,
Although there are various shapes and manufacturing methods, generally cordierite and square cell monolithic carriers manufactured by Corning and Nippon Glass Co., Ltd. are often used. This cordierite monolithic support has a very small specific surface area of about 1 m ² /g, so even if a catalytic metal such as a noble metal is supported, it cannot be dispersed on the surface of the support. As a result, a catalyst with poor initial performance and durability is obtained, and it is not practical to use it as a carrier as it is. Therefore, in order to solve the conventional drawbacks mentioned above, monolithic carriers were
It has been attempted to form an activated alumina film to increase the specific surface area, improve the dispersibility of the catalyst metal, and improve performance. At the same time, a promoter component is also supported. Various techniques have already been disclosed for forming an activated alumina coating on a monolithic carrier, but there are broadly three types. (1) A method in which activated alumina powder is dispersed in water and milled to reduce the particle size to create a stable slurry, in which a monolithic support is immersed and dried and fired to form an activated alumina film; (2) saturation. or in concentrated aluminum nitrate aqueous solution.
A method in which a carrier is immersed, dried and fired to form an activated alumina film, and (3) activated alumina powder and a binder component such as aluminum nitrate or alumina sol are mixed to form a slurry. This is a method in which the carrier is immersed in this slurry and then dried and fired to form an activated alumina film (Tokuko Sho
Publication No. 30-1570, Publication No. 55-1818, Special Publication No.
50-9749, Japanese Patent Publication No. 56-13500, Japanese Patent Publication No. 56-27295, and Japanese Patent Publication No. 53-135898). The most common methods for forming activated alumina films in recent years have been the following two methods, as a result of various improvements made from the above three methods. Namely, (1) a method of mixing activated alumina powder and an acidic aqueous solution and then finely pulverizing the mixture to form a slurry (as disclosed in Japanese Patent Application Laid-open No.
53-135898), and (2) a method of mixing activated alumina powder, a binder component, and water to form a slurry (Japanese Patent Publication No. 1983-
13500, Special Publication No. 1818 and Special Publication No. 1818-
No. 9749). Furthermore, there are three methods for incorporating a metal having a promoter effect into a film. That is, (a) as described above, a method in which a film is formed by various activated alumina coating methods and then supported by an impregnation method using an aqueous metal salt solution, such as an aqueous nitrate solution (Japanese Patent Publication No. 56-13500) (b) A method of mixing a composite oxide powder of activated alumina and a metal oxide (e.g. cerium oxide) with an acidic aqueous solution, and then finely pulverizing the resulting slurry and adhering it to a carrier (Japanese Unexamined Patent Publication No. 53 (c) a method of preparing a slurry from activated alumina, a water-soluble aluminum salt, lanthanum carbonate, and water, and depositing the slurry on a carrier (Japanese Patent Application Laid-Open No. 122044/1982). [Problems to be Solved by the Invention] There are broadly three evaluation items when forming activated alumina particles. In other words, (1) practicality as a slurry, in other words, it is better to have a viscosity of about 300±200 cps and less thixotropy, (2) good catalytic performance after catalyticization, and (3) strength of the coating. is sufficient. It is difficult for catalysts produced by conventional methods for forming activated alumina films to satisfy all of the above three points, and one of these points is sacrificed. In other words, (1) the method of finely pulverizing a mixture of activated alumina powder and acidic aqueous solution produces thixotropy and increases viscosity;
It is possible to produce only about 50% by weight (preferably 35 to 45% by weight), and as a result, a film with low strength is obtained. In addition, in the method (2) of mixing activated alumina powder, a binder component, and water to form a slurry, if a large amount of the binder component is used, the catalyst performance deteriorates and this also does not give good results. The above-mentioned problems of forming an activated alumina film also apply to the above-mentioned method of forming a film containing a metal that has a cocatalyst effect, but it is also necessary to support the film in a way that best exhibits the cocatalyst effect. It is. All conventional methods tend to cause reactions with alumina and are not preferred for containing pure metal oxides. [Means for solving the problems] This invention solves the problems of the above-mentioned prior art,
The present invention provides a manufacturing method for obtaining a catalyst carrier having excellent catalytic activity and sufficient coating strength using a novel method for forming an activated alumina coating. Therefore, the method of the present invention provides an acidic aqueous solution containing activated alumina powder having an average particle size of 20 μm or less and at least one metal oxide selected from rare earth metal oxides, cobalt oxide, and zirconium oxide. The slurry obtained by mixing is applied to an integrated structure carrier, and then fired to form activated alumina 50-99
% by weight and at least one metal oxide as mentioned above 1
It is characterized by producing a catalyst support with a coating consisting of ~50% by weight. The activated alumina powder used in the method of this invention must have an average particle size of 20 μm or less in order to improve the stability of the slurry and prevent sedimentation. In addition, the specific surface area of activated alumina is 75% in order to improve the heat resistance of the catalyst carrier.
It is preferable that it is below ^m2 /g. The content of the metal oxide having a promoter effect in the film of the catalyst carrier obtained by the method of this invention is 1 to 50% by weight, and the content of activated alumina is 50 to 99% by weight. The content percentage of metal oxide is
When it exceeds 50% by weight, the amount of activated alumina decreases,
This is because it is not possible to secure the specific surface area necessary to increase the dispersibility on the support surface when supporting the catalyst metal, and even if the content exceeds 50% by weight, the promoter effect will not increase further. This is because you cannot expect it. In addition, the content of metal oxides is 1% by weight.
If it is less than that, the stability and dispersibility of the slurry cannot be ensured, and the promoter effect cannot be exhibited. In addition,
It is preferable not to perform pulverization after mixing the activated alumina powder and the metal oxide. The slurry used in the method of this invention is
It is preferable that the solid content is 50% by weight or more in order to obtain a stable and highly dispersible slurry. Furthermore, the firing temperature after adhering the slurry to the monolithic carrier and drying it is preferably 250°C to 800°C. The rare earth metal oxides used in the method of this invention include cerium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide, yttrium oxide,
Suitable examples include samarium oxide, gadolinium oxide, ytterbium oxide, dysprosium oxide, erbium oxide, holmium oxide, and terbium oxide. The catalyst metal supported on the catalyst carrier obtained by the method of the present invention is preferably platinum, palladium, or rhodium. [Function] In the method of this invention, an acidic solution of at least one metal oxide selected from rare earth metal oxides, cobalt oxide, and zirconium oxide is contained in the slurry to ensure stability and dispersibility of the slurry. death,
In addition, the viscosity of the slurry is adjusted to improve the film strength, and it also functions as a co-catalyst component of the exhaust gas purification catalyst. Further, in the method of the present invention, by using alumina powder with an average particle size of 20 μm or less, slurry stability and dispersibility are improved, and film strength is improved. Note that by using a slurry with a solid content of 50% by weight or more, it is possible to obtain a slurry that is more stable and more dispersible, and to further improve the strength of the pear coating. Furthermore, as activated alumina powder, the specific surface area is 75
When using a material with a specific surface area of 75 m ² /g or less, it is stable even when exposed to high heat because it has been baked in advance to a specific surface area of 75 m ² /g or less. Furthermore, the metal oxide used in the method of this invention exhibits particularly excellent cocatalyst effects at high temperatures of 700°C or higher. Therefore, the method of the present invention makes it possible to obtain a heat-resistant catalyst carrier. Note that γ-alumina is added in advance.
If activated alumina is calcined at a temperature of 900° C. or lower and transformed into δ-θ-alumina, a catalyst carrier with even better high-temperature durability can be obtained. [Example] Example 1 The average particle diameter is 11.2 μm and the specific surface area is 75 m ² /
950 g of activated alumina powder, 50 g of cobalt oxide with an average particle size of 15 μm, 600 g of water, and 30 g of nitric acid were mixed and stirred for 3 hours using a Yamato Lab Stirrer to uniformly disperse the powder to prepare a coating slurry. The slurry thus prepared had a solid content of 60.9%, a pH of 4.1, and a viscosity of 320 cps. A cylindrical monolith carrier made of cordierite (manufactured by Nippon Glass Co., Ltd., diameter 93 mm, length 100 mm, volume 0.679) having 300 cells per square inch is immersed in water, and after absorbing sufficient water, it is taken out and the cells are removed. The water remaining inside was blown away with an air stream (pressure of 5 kg/cm ² ). The imbibed carrier was immersed in the previously prepared slurry for 15 minutes, taken out, and the excess slurry in the cell was blown away using a stream of air. In this way, the carrier with the activated alumina slurry attached is
After drying at 110℃ for 1 hour, it was heated to 3000℃ in the air using an electric furnace.
The catalyst carrier was calcined for 1 hour at ℃ to form an activated alumina coating of 86 g on the carrier. Next, this catalyst carrier is immersed in a platinum ammine aqueous solution to adsorb the catalyst metal platinum on the catalyst carrier, and then washed with water.
Subsequently, the catalyst carrier was immersed in an aqueous rhodium chloride solution to support the catalyst metal rhodium, and then
After drying at 100°C, it was calcined at 500°C for 30 minutes to obtain a catalyst for purifying automobile exhaust gas. Chemical analysis of the amount of precious metals supported on this catalyst revealed that the amount of platinum supported was 1.0g/-catalyst, and the amount of rhodium supported was 1.0g/-catalyst.
It was 0.1g/-catalyst. Examples 2 to 6 Instead of cobalt oxide in Example 1, yttrium oxide (Example 2), zirconium oxide (Example 3), cerium oxide (Example 4), lanthanum oxide (Example 5), and praseodymium oxide ( A catalyst carrier was obtained in the same manner as in Example 1 except that Example 6) was used. A catalyst metal was supported on this catalyst carrier in the same manner as in Example 1 to obtain a catalyst for purifying automobile exhaust gas. Comparative Example 1 1000 g of activated alumina powder with an average particle diameter of 25.1 μm and a specific surface area of 154 m ² /g, 1800 g of water, and 80 g of nitric acid were mixed and stirred for 1 hour using a Yamato lab stirrer, and then transferred to a ball mill for 17 hours. Wet milled. The slurry thus prepared had a solid content of 34.7%, a pH of 2.82, and a viscosity of 1100 cps.
A monolithic cordierite carrier (manufactured by Nippon Glass Co., Ltd., diameter 93 mm, length 100 mm, volume 0.679) having 300 cells per square inch was immersed in water to absorb sufficient water, and then taken out and left inside the cells. The water was blown off with a stream of air (pressure of 5 Kg/cm ² ). Add this water-absorbed carrier to the previously prepared slurry for 15 minutes.
After soaking for a minute and removing, excess slurry remaining in the cell was blown away using a stream of air. The carrier to which the activated alumina slurry was attached in this way was heated to 110°C.
After drying for 1 hour at 700℃ in air using an electric furnace,
A 43.2 g activated alumina film was formed on the carrier by firing for a period of time to obtain a catalyst carrier. Next, this catalyst carrier is immersed in a platinum ammine aqueous solution to adsorb platinum as a catalytic metal on the catalyst carrier, and then washed with water, and subsequently immersed in an aqueous rhodium chloride solution to support rhodium as a catalytic metal on the catalyst carrier, The mixture was then dried at 100°C and fired at 500°C for 30 minutes to obtain a catalyst for purifying automobile exhaust gas. Chemical analysis of the amount of precious metal supported on this catalyst revealed that the amount of platinum supported was
1.0g/- catalyst, amount of rhodium supported is 0.1g/-
It was a catalyst. Examples 7 to 8 and Comparative Examples 2 to 3 The catalyst supports obtained in Example 1 and Comparative Example 1 were impregnated with an aqueous palladium chloride solution and further subjected to a reduction treatment with sodium borohydride. A catalyst was obtained by supporting the catalyst metal with rhodium. The supported amounts were palladium 0.5 g/-catalyst, platinum 0.5 g/-catalyst, and rhodium 0.1 g/-catalyst (Example 7 and Comparative Example 2). Further, in the same manner as the above catalyst preparation method, palladium 1g/-catalyst and rhodium 0.1g/-
- Catalysts with supported catalysts were also prepared (Example 8 and Comparative Example 3). Performance Evaluation Test Results Performance evaluation tests were conducted on the catalysts obtained in Examples 1 to 6 and Comparative Example 1. Performance evaluation was carried out by two types: a peel test using air flow (5 kg/cm ² ) and a catalyst durability test. The peeling test conditions were as follows: spraying air flow (5 kg/cm ² m ² ) onto the coated film of the new catalyst for 10 minutes with an air gun;
The peeled amount of the coat layer was determined in weight % and was defined as the peeling rate. The catalyst durability performance test conditions are as shown below. In other words, the durability test conditions were an engine with a displacement of 3400 c.c., a rotation speed of 3600 rpm, and a boost of -300 mm.
Hg, catalyst inlet gas temperature 750℃, air fuel ratio (A/F)
14.8, the catalyst is exposed to exhaust gas for 50 hours. The performance of the durable catalyst was evaluated using an engine with a displacement of 1600 c.c.
2600rpm, boost - 360mmHg, catalyst inlet gas temperature
This is done by passing exhaust gas through the catalyst after durability at 460℃ and A/F 14.5, and calculating the purification rate for hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ). Ta. These results are shown in Table 1.

[Table] Furthermore, the catalysts obtained in Examples 7 and 8 and Comparative Examples 2 and 3 were evaluated for their performance after durability in the same manner as above, and the results are shown in Table 2.

[Table] [Effects of the Invention] As is clear from the above results, the method of the invention of this application can provide a catalyst carrier with strong coating strength and excellent catalytic activity.

Claims (1)

[Claims] 1. Mixing an acidic aqueous solution containing activated alumina powder with an average particle size of 20 μm or less and at least one metal oxide selected from rare earth metal oxides, cobalt oxide, and zirconium oxide. After attaching the slurry obtained by this process to an integral structure carrier,
Activated alumina 50-99% by weight consisting of calcining
and a method for producing a catalyst carrier having a coating comprising 1 to 50% by weight of at least one of the above-mentioned metal oxides. 2. The method for producing a catalyst carrier according to claim 1, wherein the activated alumina has a specific surface area of 75 m ² /g or less. 3. The method for producing a catalyst carrier according to claim 1, wherein the solid content of the slurry is 50% by weight or more.