The selective catalytic reduction of NOx over a Cu/ZSM-5/SAPO-34 composite catalyst

Abstract

A series of Cu/ZSM-5/SAPO-34 (Cu/ZS-PM) composite catalysts with fixed Cu amount and varying ZSM-5 mass fraction were synthesized using a pre-seed method, and their catalytic performances were tested for selective catalytic reduction (SCR) of NO with NH₃. The catalysts were characterized by means of XRD, FT-IR, SEM, BET, UV-vis DRS, NH₃-TPD, H₂-TPR and in situ DRIFTS. The results indicate that the high deNO_x performance of the Cu/ZS-PM-15% catalyst was due to the excellent redox property and the formation of NO₂. The acidity of the catalysts was significantly influenced by the content of ZSM-5 seeds, whereas there was no obvious correlation between acid strength and NH₃-SCR performance. The in situ DRIFTS spectra demonstrated that both Lewis and Brønsted acid sites are involved in the NH₃-SCR reaction and the reaction on Brønsted acid sites is more active than that on Lewis acid sites. NO₂ is a primary intermediate following NO adsorption on Cu/ZS-PM catalysts, which may promote a “fast” SCR reaction at low temperature.