Patent ID: 8580216

Claim:
A catalyst system for removing nitrogen oxides from an exhaust gas by reduction with a reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds, wherein said exhaust gas contains nitrogen oxides and oxygen in an amount larger than a stoichiometric amount relative to unburned components in said exhaust gas, said catalyst system having an inlet side and an outlet side, said catalyst system comprising: a first catalyst comprising: approximately 0.2 to approximately 15 weight percent of at least one silver component selected from the group consisting of silver and silver compounds; and at least one first inorganic oxide support, wherein the silver component is supported on the first inorganic oxide support; and a second catalyst comprising: approximately 1 to approximately 30 weight percent of a modifier oxide comprising cerium oxide, copper oxide and manganese oxide, wherein the catalyst system does not comprise tungsten oxide or vanadium oxide; and at least one second inorganic oxide support comprising at least one zeolite, wherein at least one of the second inorganic oxide supports is an acidic inorganic oxide support, wherein the modifier oxide is supported on the second inorganic oxide support, wherein the weight percent of the silver component is on the basis of silver metal relative to the weight of the first inorganic oxide support, and wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the second inorganic oxide support said first catalyst and said second catalyst being disposed in that order from the inlet side to the outlet side of said catalyst system.