Selective Removal of Acid Sites in Mordenite Zeolite by Trimethylchlorosilane Silylation to Improve Dimethyl Ether Carbonylation Stability

Catalysis research always pursues more efficient catalysts and realizes selectivity-controlled conversion. The local environment of acid sites in a zeolite is regarded as the vital reason for its catalytic selectivity in many chemical reactions. Herein, we have demonstrated that the acid sites in the 12-membered-ring (12-MR) channels of mordenite zeolite could be selectively covered by a trimethylchlorosilane (TMCS) silylation treatment, which could significantly improve the dimethyl ether (DME) carbonylation performance. Detailed mechanism studies by in situ DRIFT, 1H MAS NMR, and FTIR spectra analyses indicate that the TMCS species replace the Brønsted H+ in the bridging hydroxyl groups when chloro groups are rapidly hydrolyzed by the protons, accompanied by the formation of siloxane bonds. Due to the space limitation, the silylation reaction mainly occurred in the 12-MR channels and created most of the remaining acid sites (80%) in the 8-MR channels of the MOR zeolite, which gave better selectivity and a much longer lifetime in the DME carbonylation reaction. This work realizes a conceptual pathway to selectively control the distribution of acid sites within different confinement positions of zeolites to improve the catalytic selectivity of catalysts.