Unveiling Zeolite-Confined Aromatic-Water Dynamic Interplay in Methanol-to-Olefins Catalysis.

Water-induced structural dynamics of zeolite framework have been extensively explored in binary model systems comprising only water and zeolites. However, under practical zeolite catalytic systems, water coexists with organic guest molecules within the confined microporous environment, giving rise to dynamical and multicomponent host-guest interactions. Combining in situ spectroscopic characterization with theoretical calculations, this study unveils, at the molecular level, the dynamic ternary interplay among zeolite, confined aromatics, and water during SAPO-34-catalyzed methanol-to-olefins (MTO) reaction. The confined aromatics generated in situ spatially and electronically modify the zeolite framework, forming a molecular shield that protects the zeolite framework from hydrolytic attack. More importantly, water acts as a molecular scissor, continuously trimming the alkyl side-chains of confined aromatics, thereby retarding their polycyclic growth while promoting the efficient and sustained formation of light olefins. Across a series of eight-membered-ring (8-MR) zeolites (SAPO-34, SAPO-18, and SSZ-13), co-feeding water results in an orders-of-magnitude enhancement of catalyst lifetime while maintaining stable olefin production. The dynamic cooperative interplay among zeolite, confined aromatics, and water governs the framework stability and catalytic longevity during MTO conversion. This mechanistic insight extends the conceptual boundaries of zeolite host-guest chemistry and opens new avenues for harnessing the beneficial role of water in zeolite catalysis.