Patent ID: 8398943

Claim:
A method for reducing the nitrogen oxide content in the exhaust gas of an internal combustion engine, including the steps of: a) providing a first SCR catalyst; b) disposing an NH 3 -oxidation catalyst downstream of said first SCR catalyst, c) disposing at least one second SCR catalyst downstream of said NH 3 -oxidation catalyst, wherein said first SCR catalyst, said NH 3 -oxidation catalyst and said at least one second SCR catalyst collectively comprise a catalyst combination; d) adding ammonia and/or ammonia-containing reduction agent to an exhaust gas stream upstream of said catalyst combination such that a mixture of exhaust gas and ammonia is present upstream of said first SCR catalyst; e) dimensioning said NH 3 -oxidation catalyst, and selecting an amount for said reduction agent, such that a residual quantity of ammonia is still present in the exhaust gas stream downstream of said NH 3 -oxidation catalyst; and f) converting said residual quantity of ammonia, along with nitrogen oxides formed at said NH 3 -oxidation catalyst, into nitrogen and water vapor via said at least one second SCR catalyst.