HC-SCR for Diesel NOx Reduction on Supported Metal Catalysts

Richard  Blint, GM R&D Center

Richard Blint, Steven J. Schmieg and Michael B. Viola
General Motors R&D Center, Chemical and Environmental Sciences Laboratory
General Motors R&D Center
30500 Mound Rd
Warren, MI 48090-9055

The SCR of NO using hydrocarbons (HC-SCR) has been studied extensively as a potential alternative method for the removal of NOx under oxygen-rich conditions . HC-SCR utilizes the fuel on board the vehicle as the NOx reductant, and does not require the complex engine control and large amounts of expensive platinum-group metal catalysts employed in NOx storage catalyst systems. While the conversion efficiencies reported in the literature are commonly > 80% over various temperature ranges, the adaptability of these results to the reduction of NOx from light-duty diesel exhaust is difficult.  A unique catalyst developed using high-throughput discovery techniques in collaboration with BASF Corporation was investigated at General Motors under simulated diesel engine exhaust feed conditions for the selective catalytic reduction of NOx as part of a Department of Energy (DOE) supported cooperative project (DE-FC26-02NT41218). Consequently 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 were measured in a laboratory flow reactor system. NOx reduction over Ag/Al2O3 catalysts in a laboratory flow reactor system using a simulated diesel fuel mixture will be presented at the temperatures, flow rates, and inlet NOx concentrations likely to be encountered by a HC-SCR catalyst system on a light-duty compression ignition direct injection (diesel) vehicle under the FTP, US06, and HWYFET test schedules. In addition, using a V6 turbo charged diesel engine connected to a dynamometer running light-duty transient test cycles, NOx efficiency was evaluated as a function of catalyst volume, the hydrocarbon to NOx ratio (HC/NOx), and space velocity.

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