Surface Diffusion Barriers and Catalytic Activity Driven by Terminal Groups at Zeolite Catalysts

Defects that commonly exist on the surface of zeolitespose notablemass transport constraints and influence the catalytic performance.The mechanism underlying the surface defects inducing molecular transportlimitations, however, is not fully understood. Herein, we use versatilespectroscopy, imaging techniques, and multiscale simulations to investigatethe effect of surface defects on the molecular surface transport inzeolites, intending to establish the terminal structure-masstransport-performance relationship. Isolated silanol, whichrepresents the foremost and eventual chemical defective accessiblesite at zeolite termination for guest molecules from the bulk fluidphase into zeolites or vice versa, is taken as a showcase. We demonstratethat isolated silanol at H-SAPO-34 zeolite termination not only enhancesthe adsorptive interaction between the polar molecules/alkenes andinterface but also narrows the local 8-membered-ring pore at the externalsurface. The exterior surface with more isolated silanol could causea higher diffusion barrier and hamper the accessibility of intracrystallineactive sites. This work is expected to shed light on the mechanismunderlying the zeolite catalyst upgrading via terminal surface modificationsat zeolites.