Particle Size Dependence of Transport Barriers in MFI Structured Zeolites

Zeolites are widely used to catalyze chemical reactions and improve selectivity to desired products through ordered, shape selective microporous channels [1]. As new microporous materials are synthesized with submicron lengthscales, bulk diffusion becomes negligible with respect to the overall timescale for flux through a particle. Surface barriers have been previously postulated to have a significant contribution to overall mass transfer in small particles. In this work, the role of guest molecule kinetic diameter, adsorption/desorption binding affinity and particle size are experimentally examined. Additionally, kinetic Monte Carlo simulations are used to probe the role of the crystal structure on molecular diffusion, including the presence of internal grain boundaries, surface pore restrictions, and total pore blockages. Mechanistic insight into the location and cause of surface barriers in MFI crystals is provided.

[1] C.Luke Williams, Chun-Chih Chang, Phuong Do, Nima Nikbin, Stavros Caratzoulas, Dionisios G. Vlachos, Raul F. Lobo, Wei Fan, Paul J. Dauenhauer, "Cycloaddition of Biomass-Derived Furans for Catalytic Production of p-Xylene," ACS Catalysis 2012, 2(6), 935-939.