Effective diffusivities in zeolites 1. Aromatics in ZSM-5 crystals

摘要: Abstract Real or apparent inconsistenceis of up to several orders magnitude exist in reported diffusivities zeolites. Some are caused by differences definition, usage, and methodologies their determination. result from operating conditions involving transport mechanisms deviating a strictly stochastic process. Diffusivities effective non-steady-state methods determination (e.g., uptake diffusivities) can be translated into applicable characterization catalytic (i.e., steady-state) behavior. For ortho -xylene other aromatic molecules ZSM-5, the these follows expectations shape selectivity; i.e., they decrease systematically with increasing minimum dimension molecules. These found invariant both temperature for 360-fold variation applied concentration. A mechanistic model activated zeolite diffusion, inernalized more than one type (energy level), is suggested useful future considerations relationship intrinsic activation energies shape, structure, molecular mechanism.