Catalyst materials for NO_x 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 NO_X 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 NO_X 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 NO_X fed to the NH₃—SCR catalyst. The oxidation catalyst comprises perovskite oxide particles.