This invention relates to a method of preparing catalytically active precious metal coatings on sintered ceramic surfaces. The catalytic coatings are comprised of a precious metal and a refractory metal oxide and are bonded to the ceramic surface by heating in air. Such coatings are useful for the oxidation of ammonia and for the selective oxidation of hydrocarbons.
The usual procedures for coating ceramic materials with precious metal catalytic surfaces require not only porosity in the surface to be coated but a relatively high surface area per unit weight. Generally, the surface area is at least about 25 square meters per gram and preferably at least about 100 square meters per gram. For catalyst supports of low surface area, the high surface area wash coat is used to enhance surface area. To assure adequate bonding of the wash coat, it is necessary that the surface pores be of a larger size than the wash coat particles. Typically, such pores should be of a size in excess of 0.5 microns and total porosity in the range of 0.1 to 0.3 cc/gm. Such catalysts typically offer limited selectivity in partial oxidation reactions.