Prikhodko, V., Pihl, J., Toops, T., Thomas, J. et al., "Selective Catalytic Reduction of Oxides of Nitrogen with Ethanol/Gasoline Blends over a Silver/Alumina Catalyst in Lean Gasoline Engine Exhaust," SAE Technical Paper 2015-01-1008, 2015, doi:10.4271/2015-01-1008.
Ethanol is a very effective reductant for nitrogen oxides (NOX) over silver/alumina (Ag/Al2O3) catalysts in lean exhaust environments. With the widespread availability of ethanol/gasoline-blended fuel in the U.S., lean gasoline engines equipped with Ag/Al2O3 catalysts have the potential to deliver higher fuel economy than stoichiometric gasoline engines and to increase biofuel utilization while meeting exhaust emissions regulations. In this work a pre-commercial 2 wt% Ag/Al2O3 catalyst was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine for the selective catalytic reduction (SCR) of NOX with ethanol/gasoline blends. The ethanol/gasoline blends were delivered via in-pipe injection upstream of the Ag/Al2O3 catalyst with the engine operating under lean conditions. A number of engine conditions were chosen to provide a range of temperatures and space velocities for evaluation of catalyst performance. High NOX conversions were achieved with ethanol/gasoline blends containing at least 50% ethanol; however, as the ethanol content of the fuel blend decreased, higher reductant dosing was needed to maintain NOX conversions of greater than 90%, which also resulted in significant hydrocarbon (HC) slip. Temperature and HC dosing were important in controlling selectivity to NH3 and N2O. At high temperatures, NH3 and N2O yields increased with increased HC dosing. At low temperatures, NH3 yield was very low, but N2O levels became significant. The ability to generate NH3 under lean conditions creates the potential for application of a dual SCR approach (HC SCR + NH3 SCR) that could reduce the fuel penalty associated with NOX reduction and/or increase NOX conversion; this strategy is discussed in this work.