CATALYST MATERIALS FOR NOx OXIDATION IN AN EXHAUST AFTERTREATMENT SYSTEM THAT USES PASSIVE AMMONIA SCR

摘要

An exhaust aftertreatment system that receives an exhaust flow from a lean-burn engine and a method for treating the exhaust flow are described. The exhaust aftertreatment system may include a three-way-catalyst, an oxidation catalyst, and a NH3—SCR catalyst. The three-way-catalyst passively generates NH3 from native NOX contained in the exhaust flow when an A/F mixture supplied to the engine is cycled from lean to rich. The generated NH3 is then stored in the NH3—SCR catalyst to facilitate NOX reduction when the A/F mixture supplied to the engine is cycled back to lean. The oxidation catalyst is located upstream of the NH3—SCR catalyst and operates to lower the NO to NO2 molar ratio of the NOX fed to the NH3—SCR catalyst. The oxidation catalyst comprises perovskite oxide particles.