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The effects of molecular size on SiO2 deposition regulated surface barriers and zeolite catalysis are probed, taking n-pentane isomerization and benzene alkylation with ethylene as model reactions. Chemical liquid deposition of SiO2 on the parent ZSM-5 sample only modifies its external surface slightly and passivates a small proportion of Brønsted acid sites. The apparent diffusivities increase significantly at 363–393K after SiO2 deposition, indicating SiO2 on ZSM-5 crystals reduces surface barriers at low temperatures. The conversion for n-pentane isomerization increases by up to 26% after SiO2 deposition, while the conversion for benzene alkylation decreases by up to 19%. Obviously, the positive effect of SiO2 deposition can be balanced out by the pore confinement effect at high temperatures, which is stronger for a larger molecule. This work provides a unique understanding of molecular size effects on surface barriers, which should serve to guide the design of zeolite catalysts. [ABSTRACT FROM AUTHOR]

A method based on particle‐resolved CFD is built and validated, to calculate the fluid‐to‐particle mass and heat transfer coefficients in packed beds of spheres with different tube‐to‐particle diameter ratios (N) and of various particle shapes with N = 5.23. This method is characterized by considering axial dispersion. The mass and heat transfer coefficients increase by 5%–57% and 9%–63% after considering axial dispersion, indicating axial dispersion should be included in the method. The mass and heat transfer coefficients are reduced as N decreases. The catalyst particles without inner holes show higher mass and heat transfer coefficients than the ones with inner holes, because of unfavorable fluid flow in inner holes. The bed of trilobes has the highest mass and heat transfer coefficients, being 85% and 95% higher than the one of spheres. This work provides a versatile method and some useful guidance for the design of packed bed reactors. [ABSTRACT FROM AUTHOR]

External surface diffusion barriers can be as important as intracrystalline diffusion resistances in affecting zeolite catalysis. This work investigates how SiO2 deposition regulates surface barriers and affects catalytic activities for the zeolites with different pore sizes and dimensionalities (i.e., ZSM-22, ZSM-5, and Beta). n-Pentane isomerization is taken as the model reaction for catalytic tests. After SiO2 deposition, the apparent diffusivities for ZSM-22, ZSM-5, and Beta increase by 5–15%, 31–52%, and 34–37%. SiO2 deposition only modifies crystal surfaces as indicated by various structural characterizations, and thus these improvements in diffusion can be only attributed to the reduced surface barriers. Besides, the apparent catalytic activities for the catalysts using ZSM-22, ZSM-5, and Beta increase by 17–69%, 19–72%, and 3–60%, after SiO2 deposition. These results show that SiO2 deposition should be a universal method to reduce surface barriers on various zeolites and to improve zeolite catalysis for the reaction of n-pentane isomerization. [ABSTRACT FROM AUTHOR]

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 SiO2 is performed to reduce surface barriers on ZSM‐5 crystals with different sizes. After SiO2 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. [ABSTRACT FROM AUTHOR]