Designed synthesis of MOR zeolites using gemini-type bis(methylpyrrolidinium) dications as structure directing agents and their DME carbonylation performance

Abstract

Mordenite (MOR) zeolite is an efficient catalyst for dimethyl ether (DME) carbonylation and syngas to ethylene conversion due to the unique confinement effect and catalytic activity in 8-membered ring (8-MR) side pockets. Herein, aiming at enhancing the distribution of acid sites in the side pockets of MOR and developing high-performance catalysts, a series of bulky gemini-type bis(methylpyrrolidinium) dications with varying methylene chain lengths (nBMPr) were designed and proved to be efficient OSDAs for MOR zeolite. The synthesis efficacy of nBMPr was revealed to be closely related with the methylene chain lengths. Compared with conventional MOR templated by tetraethylammonium hydroxide (TEAOH), nBMPr-MOR possessed an obviously enhanced Brønsted acid distribution and amounts in the side pockets, likely due to the higher charge compensation ability of nBMPr for the framework [AlO₄]⁻ of 12-MR, promoting the preferential location of Na⁺ in the side pockets. Consequently, the resultant MOR zeolites showed remarkable catalytic activity in the DME carbonylation reaction. The space-time yield of methyl acetate can reach as high as 12.5 mmol g⁻¹ h⁻¹, which is the highest value ever reported for DME carbonylation using zeolitic catalysts.