Chandra Saravanan and Scott M. Auerbach,
``Theory and Simulation of Cohesive Diffusion in Nanopores:
Transport in Subcritical and Supercritical Regimes,''
J. Chem. Phys. 110, 11000-11010 (1999).
Abstract
We have studied a lattice model of self-diffusion in
nanopores, to explore how
loading, temperature and adsorbate coupling influence benzene
self-diffusion in Na-X and Na-Y zeolites.
We propose a simple method for determining how
adsorbate-adsorbate interactions modify activation energies
of site-to-site jumps.
We apply a mean field approximation that
describes transport semiquantitatively for a wide variety of system
parameters, simplifying kinetic Monte Carlo simulations.
We also derive an analytical diffusion
theory that provides semiquantitative apparent
activation energies, and qualitatively reasonable loading dependencies.
We have found that supercritical systems exhibit three characteristic
loading dependencies of diffusion, depending upon the degree of
degeneracy of lattice sites. Subcritical diffusion systems
are dominated by cluster formation, exhibiting intriguing
loading dependencies with broad regions of constant diffusivity.
Our model for benzene in Na-X is in excellent qualitative
agreement with pulsed field gradient NMR diffusivities,
and in qualitative disagreement with tracer zero-length column
(TZLC) data. We suggest that high temperature TZLC
experiments should be performed, to test whether the coverage
of maximum diffusivity decreases with increasing temperature.
Prof SM Auerbach
29 August 2000