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Modeling Jump Diffusion in Zeolites: II. Applications Scott M. Auerbach

Summary: Modeling Jump Diffusion in Zeolites: II. Applications
Scott M. Auerbach
Department of Chemistry and Department of Chemical Engineering
University of Massachusetts, Amherst, MA 01003 USA
We review recent applications of jump models for diffusion in zeolites. We describe the results of
a coarse-grained model of the interplay between zeolite anisotropy and disorder, finding that certain
disorder patterns can change how anisotropy controls membrane permeation. We show the results
of a lattice model for single-file diffusion in zeolite membranes, demonstrating how single-file
motion is manifested in anomalous mean-square displacements at short times, and in non-intensive
Fickian self-diffusion coefficients at later times. We discuss a normal-mode analysis approach for
treating framework flexibility for tight-fitting zeolite-guest systems, showing that simulations
allowing for framework flexibility can converge is less CPU time than those that keep the
framework rigid. We then explore models of the loading dependence of self-diffusion in zeolites,
with emphasis on benzene in NaX and NaY. We enumerate the decisions that need to be made
when modeling such systems, and indicate the choices/approximations we have made for modeling
benzene in NaX and NaY. We report kinetic Monte Carlo results for the loading dependence of
benzene diffusion in NaX, which is found in reasonable agreement with NMR data, but in poor
agreement with tracer ZLC results. We then speculate on the possibility of having a subcritical
fluid adsorbed in a nanoporous material, and how such a thermodynamic state would impact


Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst


Collections: Chemistry