Dual-bed catalytic system for the selective reduction of NOx with propene

For the removal of NOx from exhausts containing excess oxygen, the selectiv e catalytic reduction of NOx using hydrocarbons (HC-SCR) is highly interest ing, especially for car applications (lean deNO(x)) [1]. Two types of HC-SC R catalysts can be distinguished. High-temperature catalysts operate at tem peratures above 573 K, showing moderate activity, and (mostly) low heat and poison resistance, but high N-2 selectivity. Low-temperature catalysts, us ually based on Pt, operate between 473 and 573 K, showing opposite features : very high activity, as well as heat and poison resistance, and a low N-2 selectivity by forming N2O. Our strategy for developing an active and stabl e deNO(x) system without N2O emission is the implementation of a separate c atalytic function for N2O removal as a second stage.