1. Field of The Invention
This invention relates to catalyts and more particularly to improved methods of applying a catalytic material to an alumina catalyst.
2. The Prior Art
A calcined alumina coated metal mesh forms an effective support for many catalytic materials. Such catalysts can have many uses, such as an oxidizing catalyst useful for burning carbon monoxide or hydrocarbons in the exhaust gas streams of internal combustion engines, or as a self-regenerating filter for removing soot and other particulate matter from diesel engine exhaust gases. The formation of an alumina coated metal mesh and the addition of catalytic materials to the alumina coated metal mesh, if desired, is disclosed in many patents including co-assinged U.S. Pat. Nos. 3,227,659; 3,231,520; 3,240,698; 3,362,783; and 3,410,651. The alumina coated metal mesh can be formed by contacting a substrate, generally a metal mesh or other metallic article having an extended surface, with a coating solution which comprises an alkali metal aluminate as set forth in the prior art. After an adherent alumina film, generally of alumina trihydrate forms on the substrate, it is calcined to produce a porous alumina film. A catalytic material can then be added to the alumina film by one of several methods which have been disclosed in the prior art. The methods include applying the catalytic material to the calcined alumina film by vapor depostiton, contacting the alumina film with a solution of the catalytic material, or applying the catalytic material as a paste onto the surface of the alumina and then further treating the combination to produce the desired catalytic structure.
Generally, in the various processes of applying a catalytic material to the alumina film coated substrate, it is desired to uniformly coat the substrate and to produce a catalytic article of highest efficiency using the smallest possible quantity of catalytic material. This is because catalytic materials are generally quite expensive, and any saving in the quantity of catalytic material necessary to perform a desired function, results in a large decrease in the cost of the finished catalytic article. The various previously disclosed methods of applying a catalytic material to an alumina film coated substrate have had various degrees of success in producing the uniform distribution of catalytic material, and of producing an efficient catalyst.