Andreas Schuring, Scott M. Auerbach, Siegfried Fritzsche
and Reinhold Haberlandt, ``On Entropic Barriers for Diffusion in Zeolites:
A Molecular Dynamics Study,'' J. Chem. Phys. 116, 10890-10894 (2002).
Abstract
The self diffusion of ethane in cation-free LTA zeolite
has been studied by MD simulations for various temperatures.
These simulations predict that the diffusivity decreases
with increasing temperature
between 150 K and 300 K for a low loading of one molecule per cage.
The rate of cage-to-cage crossings shows the same temperature dependence.
We explain this phenomenon based on an analysis of the activation entropy
that controls motion through 8-ring windows separating adjacent cages.
The diffusivity and the cage-to-cage rate constant both decrease with
temperature because heating the system moves ethane away from 8-ring
windows, on average, which increases the entropic barrier for cage-to-cage
motion.
Prof SM Auerbach
10 June 2002