JPH04180835A - Production of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain an exhaust gas purifying catalyst excellent in durability, by a method wherein a platinum group catalyst is supported on a highly active ceria powder and the supported ceria powder is mixed with an activated alumina powder to prepare a slurry which is, in turn, applied to a carrier and a platinum group catalyst is further supported on the coated carrier. CONSTITUTION:A solution containing a platinum group catalytic metal compound such as a platinum compound or a rhodium compound is brought into contact with a highly active ceria powder having a specific surface area of 100m<2>/g or more and the impregnated ceria powder is subsequently baked to obtain a platinum group catalyst supported ceria catalyst powder. Next, this ceria catalyst powder and an activated alumina powder are mixed to prepare a slurry which is, in turn, applied to a carrier base material and the coated one is baked. A platinum group catalytic metal is further supported on the catalyst support layer. The catalyst thus obtained is enhanced in HC and CO purifying capacity while it keeps NOX purifying capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an exhaust gas purifying catalyst that is arranged in an exhaust system of an internal combustion engine and purifies exhaust gas discharged from the internal combustion engine.

[Prior Art] For example, the exhaust system of an automobile has conventionally been provided with an exhaust gas purifying catalyst such as a monolith catalyst or a pellet catalyst. For example, in Japanese Patent Application Laid-Open No. 48-103484,
An exhaust gas purifying catalyst is disclosed in which a platinum group catalyst metal or metal oxide is supported on a catalyst carrier containing alumina.

To manufacture such a conventional exhaust gas purification catalyst,
For example, a catalyst support layer made of activated alumina is formed on a honeycomb-shaped cordierite monolith carrier base material. Then, an aqueous solution containing a water-soluble platinum group catalyst metal compound such as dinitrodiammine platinum, rhodium nitrate, palladium nitrate, etc. is brought into contact with this catalyst support layer and fired, thereby supporting the platinum group catalyst metal on the catalyst support layer. .

[Problem to be solved by the invention] The above-mentioned exhaust gas purification catalyst has HC, Co and NO
It efficiently purifies X and plays a miraculous role in pollution prevention. This exhaust gas purification catalyst fully complies with current exhaust gas regulations. However, in the future exhaust gas regulations, it is predicted that the regulations for HC and Go will be further strengthened.

The present invention was made in view of these circumstances, and
While maintaining the same NOx purification performance as before, HC and Co
The purpose is to further improve the purification performance of

[Means for Solving the Problems] The exhaust gas purifying catalyst of the present invention has a specific surface area of 100 m2/
A first step in which highly active ceria powder of Q or higher is brought into contact with a platinum group catalyst metal compound-containing solution and then calcined to form ceria/catalyst powder on which platinum group catalyst metal is supported; and ceria/catalyst powder and activated alumina powder. a second step in which a catalyst carrier base material is coated with the slurry and fired to form a catalyst support layer; and a third step in which a platinum group catalyst metal is further supported on the catalyst support layer. It is characterized by

One feature of the present invention is the use of highly active ceria powder with a specific surface area of 100 m2/q or more.

As is known, ceria has oxygen storage ability.

Therefore, highly active ceria powder with a large specific surface area has an extremely excellent oxygen storage ability and has the effect of further promoting the catalytic action of the platinum group catalyst metal. When the specific surface area becomes smaller than 100 m2/Cl, the oxygen storage performance decreases and the purification performance of the catalyst decreases.

In the first step, this highly active ceria powder is brought into contact with a solution containing a platinum group catalyst metal compound, and then fired. As a result, the platinum group catalyst metal is supported on the highly active ceria powder.

Note that the platinum group catalyst metal is selected from platinum, rhodium, and palladium. The amount supported is preferably in the range of 0.1 to 6 parts by weight per 100 parts by weight of ceria powder. Also,
The catalyst metal-containing solution is preferably a colloidal solution, and colloids produced by the PVA protection method, colloids produced by the emulsion method, colloids produced by the Turkevich method, and the like are known.

In the second step, the ceria/catalyst powder obtained in the first step and activated alumina powder are mixed to form a slurry, and a catalyst support layer is formed from this slurry. This can be done in the same manner as in the past by immersing the catalyst carrier base material in the slurry, pulling it up, blowing off the excess slurry, and firing it at a predetermined temperature. By the way, the ratio of ceria and alumina in the catalyst support layer is ceria/alumina -115 to 1 by weight.
/1 is preferable.

As the catalyst carrier base material, conventionally known ones such as a honeycomb-shaped monolith carrier base material, a pellet-shaped carrier base material, a metal carrier base material, etc. can be used as they are. The material also
The same materials as before can be used, such as ceramics such as cordierite, mullite, alumina, and spinel, and heat-resistant metals such as ferritic steel.

Note that the activated alumina powder preferably contains lanthana or a lanthanum compound that becomes lanthana upon firing. This improves the heat resistance of activated alumina, making it possible to maintain high catalytic performance for a long period of time. The content of lanthana is preferably in the range of 5 to 60 parts by weight per 100 parts by weight of activated alumina.

In the third step, a platinum group catalyst metal is roughly supported on the catalyst support layer. The catalyst metal supported here may be the same as that supported on the ceria powder in the first step, or may be different.

Further, in addition to Pi, Rh, and Pd, noble metals such as iridium, ruthenium, and osmium, or base metals such as chromium, nickel, vanadium, copper, cobalt, and manganese can be added.

The amount of the catalyst metal supported on the catalyst support layer can be selected from various values as in the past, depending on the desired performance, cost, and other conditions. This support can be carried out in a conventional manner by impregnating with an aqueous solution of a catalytic metal compound and firing.

[Operations and Effects of the Invention] In the method for producing an exhaust gas purifying catalyst of the present invention, the platinum group catalyst metal can be supported on the highly active ceria powder as large colloidal particles.

Therefore, sintering of catalyst metals and solid solution with ceria powder are prevented, and the initial purification performance can be maintained for a long period of time. Since this catalytic metal is supported on highly active ceria powder, high catalytic performance is ensured due to the oxygen storage capacity of ceria.

Furthermore, since they are colloidal particles, solid solution with ceria powder is also prevented.

Therefore, according to the manufacturing method of the present invention, an exhaust gas purifying catalyst with excellent durability can be stably manufactured.

[Example] This will be explained in detail below using examples.

(Example 1) <First step> 100 parts by weight of highly active ceria powder with a specific surface area of 130 m2/Q and a platinum colloid solution (containing 10 g/Q of platinum)
rpt colloid” manufactured by Nichō Kikinzoku Co., Ltd. 120cc
were mixed and fired at 300°C for 1 hour to form ceria/platinum powder. Furthermore, this ceria/platinum powder has Serif 1.
1.2 parts by weight of platinum is supported per 00 parts by weight.

Second Step> Next, the ceria/platinum powder and activated alumina powder containing 4% by weight of lantana are mixed at a weight ratio of 1:2 to form a slurry. Then, a cordierite monolith carrier base material was immersed in this slurry, pulled up to blow away excess slurry, and fired at 650° C. for 2 hours to form a catalyst support layer. The catalyst support layer was formed at 150 CI per p of the carrier base material, and platinum was contained at 0.6 C].

<Third Step> Next, the carrier base material with the above-mentioned support layer was immersed in a dinitrodiammine platinum aqueous solution, the excess aqueous solution was blown off, and 300
It was baked at ℃ for 1 hour to support platinum. An aqueous rhodium chloride solution was prepared in a colander, and rhodium was supported in the same manner. The amount of supported platinum per 11 carrier base materials is CL
6 and 1, and rhodium is 0.40. Therefore, the total amount of platinum supported is 1.2 g. In this way, the catalyst of this example was manufactured.

(Example 2) Palladium colloid solution (
10C as palladium] 15;! The catalyst of this example was produced in the same manner as in Example 1, except that "Pd colloid" (containing) "Pd colloid" manufactured by Tanaka Kamen Metal Co., Ltd.) was used and a palladium chloride aqueous solution was used instead of the dinitrodiammine platinum aqueous solution. did. The amount of each supported is 1.2 g of palladium and 0.4 g of rhodium per 1f of carrier base material.

(Comparative Example 1) A slurry was formed from activated alumina powder containing 4% by weight of lantana, and this was applied to the same carrier base material as in Example 1.
The mixture was then fired to form a catalyst support layer. This catalyst supporting layer is formed in an amount of 100 l per carrier base material 11.

The carrier base material having this catalyst support layer was immersed in an aqueous cerium nitrate solution, pulled up, and then the excess aqueous solution was blown off and fired, thereby supporting 50 g of ceria per 11 carrier base materials. Further, it was immersed in a dinitrodiammine platinum aqueous solution and a rhodium chloride aqueous solution in the same manner as in Example 1, and fired in the same manner as in Example 1 to obtain carrier base material 1.1! A catalyst of Comparative Example 1 was obtained in which 1.20 g of platinum and 0.4 g of rhodium were supported per catalyst.

(Comparative Example 2) A catalyst of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that dinitrodiammine platinum was replaced with palladium chloride. The respective supported amounts were 1.20 for palladium and 0.40 for rhodium per 11 carrier base materials.

(Test Example) The catalysts of Examples and Comparative Examples obtained above were subjected to durability tests under the following conditions, and then the exhaust gas components before and after passing through the catalyst were compared. The purification rate was measured for each. The results are shown in Table 1.

(1) Durability conditions A/F = 7.6 (stoichiometric) S, V = 90000h-1 Catalyst bed temperature = 900°C Durability time = 50 hours (2) Evaluation conditions A/F = 7.6 (stoichiometric) S, V = 50000h-1 Inlet gas temperature = 400°C Table 1 (Evaluation) From Table 1, the catalyst of the example is superior to the catalyst of the comparative example in the purification performance of HC, Co, and NOX after durability. It is obvious. For example, when comparing Example 1 and Comparative Example 1, both have the same amount of catalyst metal supported, but the reason why the purification performance of the catalyst of Example 1 is improved is because
It is clear that this is due to the platinum being supported on the ceria powder using a platinum colloid solution in the first step.

Patent applicant: Toyota Motor Corporation

Claims (1)

[Claims] (1) A first step in which highly active ceria powder with a specific surface area of 100 m^2/g or more is brought into contact with a solution containing a platinum group catalyst metal compound, and then calcined to obtain a ceria/catalyst powder on which the platinum group catalyst metal is supported. , a second step of mixing the ceria/catalyst powder and activated alumina powder to form a slurry, coating the slurry on a catalyst carrier base material and firing it to form a catalyst support layer, and further adding a platinum group catalyst to the catalyst support layer. A method for producing an exhaust gas purifying catalyst, comprising a third step of supporting a metal.