Spacial hindrance induced recovery of over-poisoned active acid sites in pyridine-modified H-mordenite for dimethyl ether carbonylation

Zeolite catalysts, such as H-mordenite (H-MOR), are readily deactivated by coke deposition in carbonylation reactions. Pyridine modification of H-MOR can improve its stability but can lead to an undesirable loss in catalytic activity. Herein, we report the intrinsic impact of the pyridine adsorption behavior on H-MOR and the spacial hindrance of the zeolite frameworks on dimethyl ether (DME) carbonylation at a molecular level. We discovered that acid sites at O2 positions, located on common walls of eight-membered ring (8-MR) side pockets and 12-MR channels, were active in DME carbonylation, but were unfortunately poisoned during pyridine modification. Density functional theory calculations revealed that the pyridine-poisoned acid sites at the O2 positions could be easily regenerated due to the spacial hindrance of the zeolite frameworks. Accordingly, they can be facilely regenerated by proper thermal treatment, which induces 60% promotion in the catalytic activity along with a high stability. Our findings demonstrate the determining role of O2 positions in H-MOR for DME carbonylation and provide a new avenue for the rational design of other efficient zeolite-relevant catalytic systems.