Method of associating precious metals with specific oxides in mixed oxide systems for use as catalysts

摘要

This invention provides a very low cost effective method to alter the association of precious metal catalysts with specific support oxides in mixed oxide systems. The invention includes two discoveries: 1) that the isoelectric points for the three normally-used gasoline catalyst components are significantly different and the surface charges present have significant magnitude to promote attraction and repulsion of ions or charged radicals; and 2) ammine-chloride or ammine-nitrate salts both dissociate into positively charged precious metal radicals and are stable over a very wide pH range. The pH of the impregnation solution is controlled such that the surface charge of the oxide is opposite to the charge on the precious metal radical if the metal is to be supported on that oxide, and to control the pH such that all charges on the oxide to be avoided are the same as the precious metal radical.