Patent ID: 8302379

Claim:
A method for reducing NOx emissions in an exhaust gas feedstream of an internal combustion engine, the method comprising: equipping the engine with an aftertreatment system including a catalytic device fluidly serially connected upstream of a first ammonia-selective catalytic reduction device fluidly connected upstream of a second ammonia-selective catalytic reduction device, the first ammonia-selective catalytic reduction device including a respective catalytic material comprising a first base metal, the second ammonia-selective catalytic reduction device including a respective catalytic material comprising a second base metal, wherein the first base metal has a first catalytically active temperature range and the second base metal has a second catalytically active temperature range; monitoring temperatures of the first and second ammonia-selective catalytic reduction devices; operating the engine lean of stoichiometry only when the temperature of one of the first and second ammonia-selective catalytic reduction devices is within one of the first and second catalytically active temperature ranges; modulating the engine to generate an engine-out exhaust gas feedstream including nitric oxide, carbon monoxide, and hydrogen convertible to ammonia on the catalytic device; storing the ammonia on the first and second ammonia-selective catalytic reduction devices; and reducing NOx emissions in the first and second ammonia-selective catalytic reduction devices using the stored ammonia.