Surface barriers on nanoporous particles: A new method of their quantitation by PFG NMR

The surface permeability of zeolite crystals of type NaCaA for small alkane molecules (methane and ethane) was estimated by using a novel method, analysing NMR tracer desorption measurements. It is based on the measurement of both the relative amount of tracer exchange and the corresponding effective coefficients of intracrystalline diffusion and their correlation with the results of model calculations by dynamic Monte Carlo simulations. For the two LTA specimens investigated, already in the as-synthesized zeolite crystals notable surface resistances have been observed. Surface permeabilities have been studied in dependence on temperature, sorbate and crystal size.