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

Defects that commonly exist on the surface of zeolites pose notable mass transport constraints and influence the catalytic performance. The mechanism underlying the surface defects inducing molecular transport limitations, however, is not fully understood. Herein, we use versatile spectroscopy, imaging techniques, and multiscale simulations to investigate the effect of surface defects on the molecular surface transport in zeolites, intending to establish the terminal structure–mass transport–performance relationship. Isolated silanol, which represents the foremost and eventual chemical defective accessible site at zeolite termination for guest molecules from the bulk fluid phase into zeolites or vice versa, is taken as a showcase. We demonstrate that isolated silanol at H-SAPO-34 zeolite termination not only enhances the adsorptive interaction between the polar molecules/alkenes and interface but also narrows the local 8-membered-ring pore at the external surface. The exterior surface with more isolated silanol could cause a higher diffusion barrier and hamper the accessibility of intracrystalline active sites. This work is expected to shed light on the mechanism underlying the zeolite catalyst upgrading via terminal surface modifications at zeolites.