Construction of mordenite catalysts with superacid sites for enhanced dimethyl ether carbonylation

Abstract

Dimethyl ether (DME) carbonylation to methyl acetate (MA) is a key intermediate step in ethanol synthesis. H-form mordenite (HMOR) efficiently catalyzes this reaction, with Brønsted acid sites (BASs) serving as the active sites. The catalytic performance strongly depends on the strength of BASs. Modification of zeolites with extraframework species is a common method to tune acid strength, among which three-coordinated Al can generate superacid sites by synergistically interacting with Brønsted acid sites. In this study, we employed an ion-exchange method to introduce three-coordinated Al in MOR and systematically investigated their effect on DME carbonylation. ³¹P MAS NMR spectra confirmed that the interaction between three-coordinated Al and BASs led to the formation of superacidic sites. Reactivity results showed that although the total number of BASs decreased after the introduction of three-coordinated Al, the catalytic performance improved significantly, with a 40% increase in the space–time yield of methyl acetate (STY_MA). Mechanistic studies further revealed that these superacidic BASs facilitate the DME dissociation step, accounting for the enhanced activity. These findings provide a systematic strategy for effectively regulating BAS strength in zeolites and offer valuable insights into the rational design and optimization of zeolite catalysts for important industrialized processes.