Performance Evaluation and Application of Diesel NOx-SCR Catalyst by Ethanol Reductant

A catalyst surfaced on Ag/Al₂O₃ substrate for the selective catalyst reduction (SCR) of NOx by ethanol was evaluated in a diesel engine, and the effect of the catalyst on the reduction of NOx from the diesel engine under the EURO III ESC test modes was also investigated. The reductant injecting device was designed by means of computational fluid dynamics (CFD) analysis, and the engine test bench including the reductant injection system for the evaluation of the NOx-SCR catalyst performance was established. On the bench, the SCR catalyst with the ethanol reductant was tested at different temperatures and space velocities (SV), and integrated with an oxidation catalyst to reduce the diesel exhaust emissions of NOx, HC and CO. Under the conditions of the SV=30,000 h^-1 and the exhaust temperature range of 350∼420°C, the NOx conversion efficiency is high over 90% and low beyond the temperature range. The catalyst performance will be greatly deteriorated when the space velocity is large than 40,000 h^-1. With the increase of the ethanol injection quantity, the NOx conversion is increased, but the CO and THC emissions are undesirably increased simultaneously. By optimizing the strategy of the ethanol dosing, the integration of the NOx SCR catalyst and the CO/HC oxidation catalyst can reduce the emissions from the diesel engine to meet more stringent emission regulations.