JPH0480737B2 - - 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 monolith support has a very small specific surface area of about 1 m ² /g, so even if a catalyst metal such as a noble metal is supported, it cannot be dispersed on the support surface. As a result, initial performance,
Only catalysts with inferior durability and performance can be obtained, and it is not practical to use them as is as a carrier. In order to solve the above-mentioned drawbacks, conventional methods have been to form an activated alumina coating on a monolithic carrier 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. Generally, there are various methods for forming an activated alumina coating on a monolithic carrier, but as a result of various improvements, the following two methods have become the most common methods in recent years. Namely, (1) a method in which activated alumina powder and an acidic aqueous solution are mixed and then finely pulverized to form a slurry (as disclosed in JP-A-Sho);
53-135898) and (2) a method of mixing activated alumina powder, a binder component, and water to form a slurry (Special Publication No. 1987-
13500, Special Publication No. 55-1818, Special Publication No. 50-9749)
It is. In addition, conventional methods for incorporating rare earth metals etc. that have a cocatalyst effect include (a) using a complex oxide of alumina and rare earth metals with a high specific surface area, as shown in the example of JP-A-53-135898; A method in which the slurry obtained by forming a slurry with acid and water and further pulverizing it with a ball mill is attached to a carrier and drying and baking; A method of preparing a slurry with alumina, a binder component such as alumina sol, and water, adhering the slurry to a carrier, drying and firing, impregnating it with a rare earth metal salt aqueous solution, drying and firing to support it, and (c) a special method. As disclosed in Japanese Patent Publication No. 122044/1984, there is a method in which a slurry is prepared from activated alumina, a water-soluble aluminum salt, lanthanum carbonate, and water, and the slurry is adhered to a carrier and dried and fired. [Problems to be Solved by the Invention] The conventional method for forming an activated alumina film has the following problems. In other words, (1) the method of finely pulverizing a mixture of activated alumina powder and acidic aqueous solution produces thixotropy;
Furthermore, since the viscosity increases, the solid content can only be reduced to about 20 to 50% by weight (preferably 35 to 45% by weight), resulting in a film with weak strength.
In addition, (2) in the method 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. Furthermore, the conventional method of incorporating rare earth metals and the like has the following problems. In other words, in conventional technology (a), since there is no binder component in the slurry, wet pulverization is performed to maintain the film strength, but the strength is insufficient as a catalyst for purifying automobile exhaust gas used at high gas flow rates. It is enough. In addition, in the technique (b), since the slurry contains a binder component, the coating strength is sufficient, but this has a negative effect on the catalyst performance. This is because alumina hydrate, which is a binder component, becomes alumina after calcination, but its activity is lower than that of γ-alumina, which is a so-called alumina powder, and its dispersibility when supporting a catalyst metal is poor. Moreover, since the process requires two steps, it is also disadvantageous in terms of cost. On the other hand, although technology (c) is good in that it improves the drawbacks of (a) and (b), it still has poor catalyst performance because it uses a water-soluble aluminum salt as a binder component. It's not good for Therefore, there has been a desire for a method of forming an alumina coating containing rare earth metals by a simple process that does not use a binder component, has sufficient coating strength, and has sufficient coating strength. [Means for Solving the Problems] The present invention solves the problems of the prior art described above, and aims to obtain a catalyst carrier with excellent catalytic activity and sufficient film strength by a novel method for forming an activated alumina film. The present invention provides a method for manufacturing. Therefore, the method of the present invention involves mixing activated alumina powder with an average particle size of 20 μm or less and an acidic aqueous solution of at least one metal salt selected from rare earth metal salts, cobalt salts, and zirconium salts. The resulting slurry is applied to a monolithic structural support and then calcined to form a catalyst support having a coating consisting of 50-99% by weight of activated alumina and 1-50% by weight of oxide of at least one of the metals mentioned above. It is characterized by manufacturing. 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 1 to 50% by weight.
50-99% by weight. Metal oxide content is 50
This is because if the amount exceeds % by weight, the amount of activated alumina decreases, making it impossible to secure the specific surface area necessary to improve the dispersibility on the carrier surface when supporting the catalyst metal. Furthermore, if the content of the metal oxide is less than 1% by weight, the stability and dispersibility of the slurry cannot be ensured, and the promoter effect cannot be exhibited. Furthermore, the slurry used in the method of this invention has a pH of 3 to 5.5 and a solid content of 50% by weight.
The above are preferred in order to obtain a stable and highly dispersible slurry. 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 salts used in the method of this invention include cerium nitrate, lanthanum nitrate, praseodymium nitrate, neodymium nitrate, yttrium nitrate, samarium nitrate, gadolinium nitrate, ytterbium nitrate, dysprosium nitrate, erbium nitrate,
Holmium nitrate, terbium nitrate, etc. are suitable. 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 the present invention, at least one metal salt selected from rare earth metal salts, cobalt salts, and zirconium salts is contained in the slurry to ensure the stability and dispersibility of the slurry and improve the coating strength. In addition to improving the performance, it also acts as a co-catalyst. In addition, in this invention method, the average particle size is 20 μm.
By using the following alumina powder, the stability and dispersibility of the slurry are improved and the strength of the coating is improved. By using a slurry with a pH of 3 to 5.5 and a solid content of 50% by weight or more, the slurry can be made more stable and more dispersible, and the strength of the coating can be further improved. Furthermore, as activated alumina powder, the specific surface area is 75
When using a catalyst carrier 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 sintered in advance to a specific surface area of 75 m ² /g or less, making it a heat-resistant catalyst carrier. becomes possible. Note that if γ-alumina is previously calcined at a temperature of 900°C or higher and transformed into δ-, θ-, and alumina and used as the activated alumina, a catalyst carrier with even better high-temperature durability can be obtained. [Example] Example 1 510 g of previously calcined activated alumina powder with a specific surface area of 56 m ² /g and an average particle size of 9.3 μm was added to 500 ml of an aqueous solution of 0.64 mol/cerium nitrate and stirred for 1 hour using a Yamato lab stirrer. A slurry for coating was prepared by mixing and stirring. The solid content of this slurry was 56.4%, the pH was 3.35, and the viscosity was 540 cps. A porous, water-permeable cordierite monolith carrier (manufactured by Nippon Glass Co., Ltd., diameter 93 mm, length 100 mm) with 300 cells per square inch is immersed in water to absorb sufficient water, then taken out and air-filled. After blowing off the water remaining in the cell with a stream (5 kg/cm ² ), the cell was immersed in the slurry prepared earlier for 15 minutes. The carrier is then removed, excess slurry remaining in the cell is blown away with a stream of air, and the carrier is removed.
Dry with ventilation at 110℃ for 30 minutes, then heat in air using an electric furnace.
The mixture was fired at 700°C for 1 hour to form a film on the carrier to obtain a catalyst carrier. The weight increase due to the formed film is
It was 76g. Next, this catalyst carrier is immersed in a platinum ammine aqueous solution to adsorb the catalytic metal platinum onto the catalyst carrier, and then washed with water and subsequently immersed in a rhodium chloride aqueous solution to support the catalytic metal rhodium on the catalyst carrier. After drying at 100℃, 30 at 500℃
A catalyst for purifying automobile exhaust gas was obtained by firing for a minute.
Chemical analysis of the amount of noble metal supported on this catalyst revealed that the amount of platinum supported was 1.0 g/-catalyst and the amount of rhodium supported was 0.1 g/-catalyst. Examples 2 to 6 Using the preparation method of Example 1, instead of the dispersion liquid in which activated alumina powder is dispersed (cerium nitrate aqueous solution in Example 1), yttrium nitrate aqueous solution (Example 2), zirconium nitrate aqueous solution (Example 2), zirconium nitrate aqueous solution Example 3),
Aqueous cobalt nitrate solution (Example 4) A catalyst carrier was obtained in the same manner as in Example 1, except that an aqueous lanthanum nitrate solution (Example 5) and an aqueous praseodymium nitrate solution (Example 6) were used. A catalyst metal was further 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 previously calcined 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 placed in a pole mill. Utsushi was wet-milled for 17 hours. The slurry thus prepared had a solid content of 34.7%, a pH of 2.82, and a viscosity of 1100 cps. Porous, water-permeable cordierite monolith carrier with 300 cells per square inch (manufactured by Nippon Glass Co., Ltd., diameter 93 mm, length 100 mm, volume
0.679) in water and let it absorb enough water,
Remove the water remaining in the cell with air flow (5 kg/
^cm2 ). The imbibed carrier was immersed in the previously prepared slurry for 15 minutes, removed, and the excess slurry remaining in the cell was blown away using a stream of air. After drying the carrier to which the activated alumina slurry was attached in this way at 110°C for 1 hour,
Baked in air at 700℃ for 1 hour using an electric furnace, 43.2g
A catalyst carrier was obtained by forming an activated alumina film on the carrier. Next, this catalyst carrier is immersed in a platinum ammine aqueous solution to adsorb the catalytic metal platinum onto the catalyst carrier, and then washed with water and subsequently immersed in a rhodium chloride aqueous solution to cause the catalytic metal rhodium to be supported on the catalyst carrier. 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 noble metal supported on this catalyst revealed that the amount of platinum supported was 1.0 g/-catalyst and the amount of rhodium supported was 0.1 g/-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. Supported amount is palladium 0.5g/-catalyst, platinum 0.5g/-catalyst rhodium
It was 0.1g/-catalyst. (Example 7 and Comparative Example 2) Catalysts carrying 1 g/- of palladium and 0.1 g/- of rhodium were also prepared in the same manner as the above catalyst preparation method. (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/m ² ) onto the new catalyst coating using an air gun for 10 minutes;
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.

〔Effect of the invention〕

As is clear from the above results, the inventive method of this application can provide a catalyst carrier with strong coating strength and excellent catalytic activity.

Claims (1)

[Claims] 1. A powder obtained by mixing activated alumina powder with an average particle size of 20 μm or less and an acidic aqueous solution of at least one metal salt selected from rare earth metal salts, cobalt salts, and zirconium salts. A catalyst support having a coating consisting of 50 to 99% by weight of activated alumina and 1 to 50% by weight of an oxide of at least one of the above-mentioned metals, which is obtained by depositing a slurry on an integral structural support and then sintering the slurry. manufacturing method. 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 slurry has a pH of 3 to 5.5. 4. The method for producing a catalyst carrier according to claim 1, wherein the solid content of the slurry is 50% by weight or more.