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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 NOx 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 NOx reduction activity. A dual catalyst approach using a HC-SCR catalyst followed by an NH3-SCR catalyst was also investigated.

Unique silver/alumina (Ag-Al₂O₃) catalysts developed using high-throughput discovery techniques in collaboration with BASF Corporation were investigated at General Motors Corporation under simulated lean-burn engine exhaust feed conditions for the selective catalytic reduction of NOx using hydrocarbons (HC-SCR). Hydrocarbon mixtures were used as the reductant to model the multi-component nature of diesel fuel and gasoline. Previous work has shown promising HC-SCR results in both laboratory reactor and engine dynamometer testing. This report investigates several aspects of HC-SCR catalyst durability, including thermal durability, sulfur tolerance, and hydrocarbon deactivation.

A unique catalyst developed using high-throughput discovery techniques in collaboration with BASF Corporation and Accelrys, Inc. was investigated at General Motors under simulated diesel engine exhaust feed conditions for the selective catalytic reduction of NOx. A hydrocarbon mixture was used as the reductant to model the multi-component nature of diesel fuel and the catalyst was evaluated over a wide range of temperatures (150 - 550°C) relevant to light-duty diesel exhaust. This report investigates the effects of NOx (as NO or NO2), hydrocarbon concentration level (HC:NOx ratio), oxygen concentration, NO concentration, catalyst space velocity, catalyst temperature, and the co-presence of hydrogen on steady-state NOx reduction activity. Using these results, a control strategy was developed to maximize NOx conversion over the wide-ranging exhaust conditions likely to be encountered in light-duty diesel applications.

The steady-state reduction of NOx at temperatures between 150-300°C has been investigated under simulated lean-burn conditions using a two-stage transient flow reactor system consisting of non-thermal plasma in combination with a sodium Y zeolite catalyst. Reactivity comparisons were made with and without plasma operation in order to identify the plasma-generated hydrocarbon species necessary for the selective catalytic reduction (SCR) of NOx. With propene as the hydrocarbon in the feed, NO is completely oxidized to NO2 in the plasma and the formation of oxidized carbon-containing species include formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide, and methanol. Fourier transform infrared (FTIR) measurements indicate a close carbon balance between plasma inlet and outlet gas feed concentrations, signifying the major species have been identified.

Diesel engines have the potential to significantly increase vehicle fuel economy and decrease CO₂ emissions; however, efficient removal of NOx and particulate matter from the engine exhaust is required to meet stringent emission standards. A conventional diesel aftertreatment system consists of a Diesel Oxidation Catalyst (DOC), a urea-based Selective Catalyst Reduction (SCR) catalyst and a diesel particulate filter (DPF), and is widely used to meet the most recent NOx (nitrogen oxides comprising NO and NO₂) and particulate matter (PM) emission standards for medium- and heavy-duty sport utility and truck vehicles. The increasingly stringent emission targets have recently pushed this system layout towards an increase in size of the components and consequently higher system cost. An emerging technology developed recently involves placing the SCR catalyst onto the conventional wall-flow filter.