Catalysts for Lean-Burn Engine Exhaust Aftertreatment Using Hydrocarbon Selective Catalytic Reduction

Unique silver/alumina catalysts developed in collaboration with BASF Corporation were investigated at General Motors under simulated lean-burn engine exhaust feed conditions for the selective catalytic reduction of NO_x using hydrocarbons as reductant (HC-SCR). Catalysts were evaluated using a laboratory fixed-bed flow reactor system over a wide range of temperatures relevant to light-duty and heavy-duty exhaust conditions for CIDI (compression ignition direct injection – diesel) and SIDI (spark ignition direct injection – gasoline) applications. This report investigates the effects of silver content (i.e., wt.% Ag₂O) and reductant composition (i.e., simulated diesel fuel, simulated gasoline, ethanol, and ethanol/simulated gasoline mixtures) on the steady-state NO_x reduction activity. A dual catalyst approach using a HC-SCR catalyst followed by an NH₃-SCR catalyst was also investigated. Stochastic Process Modeling was used to determine the optimum in-exhaust injection strategy using ethanol and simulated gasoline as reductants during the New European Driving Cycle.