A hydrocarbon-independent lean-burn NO.sub.x catalyst for treatment of products of combustion includes a porous support impregnated with two transition metals. The first transition metal has a stable upper oxidation state that is reducible to a lower oxidation state in the presence of carbon monoxide which is oxidized in the presence of the first transition metal to form carbon dioxide. The second transition metal has a stable lower oxidation state and is capable of being raised to a higher oxidation state in the presence of NO.sub.x which is reduced to nitrogen and oxygen in the presence of the second metal. The first and second metals cooperate to form a redox reaction system which regenerates the active form of the catalyst by raising the first metal to its stable oxidation state and reducing the second metal to it stable lower oxidation state by electron transfer between the first and second metals. The catalyst is based on transition metals which are less expensive than the noble metal-containing catalysts in current use.
Partha P. Paul; Stuart T. Schwab