Patent ID: 7666375

Claim:
A method which comprises subjecting fuel to combustion while the combustion atmosphere of fuel is oscillated periodically and alternately between rich and lean conditions, leading the exhaust gas formed to a catalytic reactor, and bringing the exhaust gas into contact with a catalyst in the catalytic reactor to conduct catalytic reduction of nitrogen oxides contained in the exhaust gas, wherein the catalyst comprises as catalyst components: (A) an oxide catalyst component A comprising (a) ceria or (b) praseodymium oxide or (c) a mixture of oxides and/or a composite oxide of at least two elements selected from the group consisting of cerium, zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum; and (B) (d) a noble metal catalyst component B comprising at least one of platinum and oxide thereof, or at least one of platinum and oxide thereof and at least one of rhodium, palladium and oxides thereof, and supported by the oxide catalyst component A; under an oxygen concentration adjusted in the range of 0.1-1.0% at the exit of the catalytic reactor under the rich conditions.