Arrangement for Reducing Nitrogen Oxides in Exhaust Gases

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 NH3-oxidation catalyst downstream of said first SCR catalyst,
• c) disposing at least one second SCR catalyst downstream of said NH3-oxidation catalyst, wherein said first SCR catalyst, said NH3-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 NH3-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 NH3-oxidation catalyst;
• and
• f) converting said residual quantity of ammonia, along with nitrogen oxides formed at said NH3-oxidation catalyst, into nitrogen and water vapor via said at least one second SCR catalyst.