HC-SCR reaction pathways on ion exchanged ZSM-5 catalysts

Metal cation (metal = Cu, In and La) ion exchanged ZSM-5 zeolites as catalysts for the NO selective reduction by propane and propene in excess oxygen. The surface reactions of HC-SCR over catalysts were investigated through in situ DRIFTS method. For C3H8-SCR, adsorbed nitrate species (–NO3) were observed as main reaction intermediates and they could react with gaseous propane to produce N2, H2O and CO2. While for C3H6-SCR, adsorbed amine species (–NH2) were observed as main reaction intermediates and they could react with NO or NO2 to produce the final products. The different reaction pathways for C3H8-SCR and C3H6-SCR over catalysts were proposed based on the DRIFTS results and the main factors controlling the activities of catalysts were discussed in details. The competing adsorption between NO–O2 and HC–O2 on the Brønsted acid sites of catalysts was responsible for the different reaction pathways in HC-SCR.