Polyfunctional catalysts

Abstract

This invention provides polyfunctional catalysts comprising a composite of platinum and one or more of rhodium, ruthenium and iridium, a substantially larger quantity of one or more base metal oxides in which the metal is selected from the group consisting of metals having an atomic number from 25 to 28 and rhenium, and an alumina support, which composite is made and then deposited on a suitable carrier. In a preferred embodiment, the catalysts contain 1-20 weight percent of said base metal oxide, typically nickel oxide; 0.05-0.5 weight percent platinum; and 0.002-0.3 weight percent rhodium, and an alumina support deposited on a monolith or other carrier. The improved catalysts are especially applicable for purifying exhaust gases from combustion processes, and in particular those from internal combustion engines. These polyfunctional catalysts have in a single formulation, the ability to accomplish four objectives - to oxidize carbon monoxide and unburned hydrocarbons while reducing nitrogen oxides, thereby converting those contaminants found in the exhaust of internal combustion engines into carbon dioxide, water and elemental nitrogen, but without producing significant amounts of hydrogen sulfide, sulfur trioxide or sulfuric acid. Such chemical conversions take place over the catalyst when the ratio of air to fuel supplied to the catalyst is controlled to nearly stoichiometric conditions, thereby maintaining the exhaust feed gases within a narrow compositional range, sometimes called a 'window,' in which the catalyst can substantially convert the contaminants.