Confinement Driving Mechanism of Surface Methoxy Species Formation in Mordenite Zeolite: An Interplay of Different Molecular Factors

W. Chen (Wei - CMM), K. A. Tarach, K. Góra-Marek, A. Zheng
Applied Catalysis B: Environmental
357, 124306


Surface methoxy species (SMS) are key intermediates in methanol conversion within zeolites. We propose a reaction mechanism for SMS formation using methanol or dimethyl ether in mordenite zeolites, based on ab initio molecular dynamics (AIMD) simulations and validated by in situ experiments. Key factors such as adsorption, diffusion, distribution, and attacking modes of reactants were considered. The forward attacking mode of both methanol and dimethyl ether on the acid site is more feasible for SMS formation than the backward mode in the 8 member-ring of mordenite (MOR-8MR). For methanol, two end-to-end molecules in MOR-8MR promote SMS formation via a stepwise pathway, avoiding the rotation of protonated methanol, while two methanol molecules on different sides of acid site hinder SMS formation. Dimethyl ether, however, converts to SMS in MOR-8MR regardless of concentration and distribution. The kinetics align with in situ Fourier transform infrared experiments and are confirmed by two-dimensional correlation analysis of methanol dehydration.