| abstract |
Catalysts, methods of preparing catalyst, and methods for treating exhaust gas streams are described. In one or more embodiments, a catalyst system includes an upstream zone effective to catalyze the conversion of a mixture of NO x and NH 3 to N 2 , and a downstream zone effective for the conversion of ammonia to N 2 in the presence or absence of NO x . In an embodiment, a method for preparing a catalyst system includes: first coating one end of a substrate along at least 5% of its length with an undercoat washcoat layer containing a material composition effective to catalyze the removal of ammonia; second coating the substrate along at least 50% of its length with an overcoat layer containing a material composition effective to catalyze the conversion of a mixture of NO x and NH 3 to N 2 . A method for treating the exhaust gas stream is provided, which includes injecting ammonia or an ammonia precursor into an exhaust gas stream of a vehicle, passing the engine exhaust gas stream containing NO x and NH 3 through the upstream zone of a catalyst system to remove NO x and then passing the exhaust gas stream through the downstream zone of the catalyst system to remove NH 3 , as well as other oxidizable species such as hydrocarbons and CO. |