JPH0350578B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a porous catalyst for purifying exhaust gases emitted from automobiles, factories, etc., combustion exhaust gases such as oil and gas, and incomplete combustion gases such as oil smoke from cooking. . Conventional technology Conventionally, porous catalysts for exhaust gas purification were developed in Japanese Patent Application Laid-Open No.
As described in Publication No. 161327, lime aluminate, fused silica, titanium dioxide, and a forming aid are mixed, water is added and kneaded, the resulting mixture is formed into a honeycomb shape, hardened and dried. The honeycomb carrier was immersed in a salt solution of platinum group metal or the like to support a metal catalyst, and then heat-treated. Problems to be Solved by the Invention However, when the honeycomb carrier obtained by the above conventional method is heat-treated at a temperature of about 1000°C,
The problem was that the specific surface area decreased and the catalyst activity decreased. The present invention solves the above conventional problems,
The object of the present invention is to provide a porous catalyst for exhaust gas purification that prevents the specific surface area from decreasing at high temperatures by improving the composition of the carrier and has high catalytic activity. Means for Solving the Problems In order to achieve this object, the present invention combines lime aluminate as a main component with fused silica as an aggregate, powder materials such as titanium dioxide and a molding aid, and rare earth oxide as a reduction co-catalyst. A honeycomb-shaped carrier obtained by mixing powders, adding water, kneading, molding into a highly porous shape, and hardening and drying is impregnated with an aqueous solution of metal salts of palladium and cerium as a catalyst, and then heat-treated. be. Effect: By this means, the specific surface area of the honeycomb carrier can be increased.
It has a large NO ₂ purification capacity of 15 to 20 m ² /g and does not change even after heat treatment at a high temperature of 1000℃, and by supporting a metal catalyst, the catalyst activity does not decrease at high temperatures and is good at low temperatures. can be obtained. Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. Example 1 The composition of the carrier was 40 parts by weight of lime aluminate, 45 parts by weight of fused silica, 5 parts by weight of titanium dioxide, 10 parts by weight of cerium oxide as rare earth oxide powder, and 3 parts by weight of carboxymethyl cellulose as a molding aid, and mixed together. Then, 18 parts by weight of water was added to the powder, and the resulting material was extruded using a honeycomb die, rapidly hardened, and dried to obtain a honeycomb carrier. The honeycomb carrier is used as a catalyst in a mixed solution of palladium and cerium.
Dip for 1 second to support 1 g of palladium and 10 g of cerium as cerium oxide, then soak at 1000°C.
Heat treatment was performed. Example 2 40 parts by weight of lime aluminate, 40 parts by weight of fused silica, 5 parts by weight of titanium dioxide as a carrier composition, 15 parts by weight of lanthanum oxide as a rare earth oxide powder, and 3 parts by weight of carboxymethyl cellulose as a molding aid were added and mixed, The same treatment as in Example 1 was performed on the material obtained by adding 18 parts by weight of water to the powder and kneading it. Example 3 The composition of the carrier is 40 parts by weight of lime aluminate, 45 parts by weight of fused silica, 10 parts by weight of titanium dioxide, 5 parts by weight of neodymium oxide as a rare earth oxide powder, and 3 parts by weight of carboxymethyl cellulose as a molding aid and mixed. The same treatment as in Example 1 was performed on the material obtained by adding 18 parts by weight of water to the powder and kneading it. Comparative example: 40 parts by weight of lime aluminate as the carrier composition.
Example 1 was prepared by mixing 45 parts by weight of fused silica and 15 parts by weight of titanium dioxide with 3 parts by weight of carboxymethyl cellulose as a molding aid, adding 18 parts by weight of water based on the powder, and kneading. The same treatment was applied. The above four types of catalysts were prepared and heat treated at 1000℃ in an electric furnace to determine the specific surface area.
Measured by BET method. The results are shown in FIG. Further, the results of measuring the nitrogen dioxide purifying ability of the four types of catalysts obtained are shown in FIG. 2, and the conditions for measuring the nitrogen dioxide purifying ability are shown in Table 1.

[Table] In the figure, 1 is Example 1, 2 is Example 2,
3 shows Example 3, and 4 shows Comparative Example. As shown in FIG. 1, in Comparative Example 4, the specific surface area decreases as the heat treatment is carried out at high temperature for a long time.
This seems to be caused by the disappearance of pores between fine particles. Examples 1 to 3 are honeycomb catalysts manufactured by adding rare earth oxide powder having a reduction catalytic action to the mixing stage, and from FIG.
Compared to Comparative Example 4, the specific surface area did not decrease much even when heat treated at a high temperature. This is considered to be because the rare earth oxide powder prevents the honeycomb carrier from sintering at high temperatures. Further, among Examples 1 to 3, Example 1 showed the least decrease in surface area. From this, although Example 2 contains more rare earth oxide powder than Example 1, it is considered that even if a large amount of rare earth oxide powder is mixed, prevention of sintering cannot be expected by itself. Moreover, as shown in FIG. 2 regarding nitrogen dioxide purification ability, Comparative Example 4 has lower performance than Examples 1 to 3. This seems to be because the amount of active metal also decreases due to sintering as well as the aforementioned decrease in specific surface area. Effects of the Invention As described above, by adding rare earth oxide powder as a reduction co-catalyst at the time of initial mixing in the manufacturing process, the specific surface area does not decrease even when heat treated at high temperature for a long time, and the catalyst activity is reduced. This has the effect that a good catalyst can be obtained.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between heat treatment temperature and BET specific surface area in Examples and Comparative Examples of the present invention;
FIG. 2 is a characteristic diagram showing the relationship between heat treatment temperature and nitrogen dioxide purification ability in the same example and comparative example.

Claims (1)

[Claims] 1. A method for producing an exhaust gas purifying catalyst having a structure in which a catalyst is supported on a highly porous carrier, the main component being lime aluminate powder, and oxidized rare earth powder as an aggregate, a molding aid, and a reduction promoter. A porous catalyst for exhaust gas purification, characterized in that palladium is supported as a catalyst on a highly porous carrier obtained by adding water to a paste-like mixture, followed by molding, curing, and drying, followed by heat treatment. manufacturing method.