Water-assisted shape-selective production of ethene in methanol-to-olefins reaction on SAPO-34

Comprehending the role of water in the methanol-to-olefins (MTO) reaction is of utmost importance. Herein, we report an unprecedented ethene selectivity of approximately 58% with water assistance during the MTO reaction over SAPO-34, along with an extension of catalyst lifespan. The in situ spectroscopic observations and isotope switching experiments revealed that naphthyl species with higher concentration were retained in SAPO-34 and exhibited higher reactivity when cofeeding water with methanol. The density functional theory calculations suggested that the water-mediated microenvironment not only activates the methanol molecules but also serves as a proton transfer reagent between the zeolite framework and the organic intermediates, contributing to a lower reaction energy barrier for ethene formation. A strategy of cofeeding water with methanol over a naphthyl-species pre-accommodated SAPO-34 catalyst is proposed, achieving an enhanced ethene selectivity up to 67.5%. The mechanistic insights and strategy development deepen the understanding of the role of water in zeolite catalysis and offer optimizations for MTO industrial applications.