Crystal-size–dependent external surface diffusion barriers in Pt/ZSM-5 catalyzed n-pentane isomerization

Surface barriers persist in the molecular transport across external crystal surface of zeolites, which brings strong influences on zeolite catalysis. This study probes the role of crystal-size–dependent surface barriers in zeolite catalysis, with n -pentane isomerization catalyzed by Pt/ZSM-5 as a model reaction system. Chemical liquid deposition of SiO 2 is performed to reduce surface barriers on ZSM-5 crystals with different sizes. After SiO 2 deposition, surface barriers on both small (266 nm) and large (1304 nm) crystals are significantly reduced, while the improvement in catalytic activity for the large crystals (76.1%–129.1%) is much higher than that for the small ones (−17.4% to 16.7%). For the large ZSM-5 crystals, diffusion limitation is stronger, and thus the effect of surface barriers on catalytic activity is more important. This study reveals the unique role of crystal-size–dependent surface barriers in zeolite catalysis, and understanding this is important for the optimal design of zeolite catalysts.