Effects of the preparation method of Cu⁃SAPO⁃34 catalysts in de-NOx SCR by propylene

Cu-SAPO-34 catalysts prepared by incipient wet impregnation (IWI), liquid ion-exchange (LIE) and one-pot (OP) hydrothermal methods were applied in selective catalytic reduction of NO with propylene (C3H6-SCR). Under diesel engine exhaust conditions containing 10% O2 and 5% H2O, Cu-SAPO-34(OP) obtained ~95% NOx conversion and ~95% N2 yield at 250–300 °C. Compared the IWI and LIE samples, the Cu-SAPO-34(OP) sample had abundant Lewis acidic sites, the largest specific surface area, and the most isolated Cu2+ species, thus it exhibited the best de-NOx performance. In contrast, more inactive CuO species formed on the surface of the LIE and IWI samples. The isolated Cu2+ ions in the 8MR rings have high reducibility, and are supposed to be the main active sites of Cu-SAPO-34 catalysts in the C3H6-SCR reaction. In situ DRIFTS suggests that isolated copper ions are favourable for the adsorption and activation of NOx and C3H6, thus enhancing the formation of isocyanate (-NCO) and -CN species, which act as key intermediates and further produce N2. This study can be helpful to provide some references for the design of HC-SCR catalyst and application of diesel NOx abatement.