Role of Brønsted Acid Sites within 8‑MR of Mordenite in the Deactivation Roadmap for Dimethyl Ether Carbonylation

Mordenite zeolite is now the most promising catalyst for the carbonylation of dimethyl ether (DME) to methyl acetate because of the excellent initial activity and selectivity, but it suffers from rapid deactivation because of the carbonaceous deposits. It is generally accepted that coking at Brønsted acid sites (BASs) in the 12-membered ring (B12‑MR) leads to the limited catalytic lifetime. However, contradictory deactivation behaviors in some cases inspire us to reveal the deactivation mechanism in DME carbonylation, which is essential for further industrialization of this important process. Herein, we mainly focus on dissecting the role of BASs in the 8-membered ring (B8‑MR) and B12‑MR in deactivation. We precisely modulated the concentration of BASs in different channels and confirmed the contribution of B8‑MR to coke formation. Based on the speculated mechanism of deactivation, kinetic studies were performed together with in-situ Fourier-transform infrared spectroscopy, gas chromatography–mass spectrometry, and temperature programmed oxidation-mass spectroscopy to determine the predominant deactivation pathway during the early stage of DME carbonylation and the specific roles of BASs especially in 8-MR were identified. This insight into the deactivation mechanism will provide inspirations for further design and modification of robust zeolite catalysts associated with the carbonylation reaction.