Imaging of Nano-Concave Surface Overcoming the Surface Diffusion Barrier in Zeolites.

Surface diffusion limitation at the interfaces of nanoporous crystals has emerged as a critical factor limiting mass transport, thereby impeding the catalytic and separation efficiencies. The crux in further optimization of nanoporous solids lies in visualizing nanoscale mass transport under confinement and correlating the observed phenomena with specific surface nanostructures. Here, we revealed that the bottom-up synthesized surface nanoconcavities markedly mitigate benzene traffic control (molecular accumulation) at the ZSM-5 nanocrystal periphery, a phenomenon indicative of surface diffusion limitation, by integrating atomic in situ low-dose scanning transmission electron microscopy with multiscale molecular dynamic simulations. Unexpectedly, the sinusoidal open pores terminated by a half Si10-ring at sidewalls of the nanoconcavity become additional accessible pathways, compared to the smooth surface, for molecular ingress and egress. Besides, the confinement inherent to nanoconcavities increases the residence time of benzene molecules on the concave surface, promoting their capture by pore mouths. This study establishes a nanoscale methodology for correlating local structure with mass transport in nanoporous materials and highlights a termination structure-engineering viewpoint for controlling surface diffusion limitation.