SMALL PORE MOLECULAR SIEVE SUPPORTED COPPER CATALYSTS DURABLE AGAINST LEAN/RICH AGING FOR THE REDUCTION OF NITROGEN OXIDES

摘要

A chemical process for treating exhaust gas from a vehicular internal combustion engine with a lean/rich cycle using a selective catalytic reduction (SCR) catalyst comprises exposing the SCR catalyst in a NOx adsorber catalyst (NAC)+(downstream)SCR catalyst system to at least one reactant including nitrogen oxides and reducing the nitrogen oxides with a nitrogenous reductant, wherein the SCR catalyst comprises copper and a small pore molecular sieve having a maximum ring size of eight tetrahedral atoms and wherein the nitrogenous reductant is metered into a flowing exhaust gas only when the SCR catalyst is at above 100°C.