 
Summary: Modeling the concentration dependence of diffusion in zeolites. III. Testing
mean field theory for benzene in NaY with simulation
Chandra Saravanan and Fabien Jousse
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
Scott M. Auerbacha)
Department of Chemistry and Department of Chemical Engineering, University of Massachusetts, Amherst,
Massachusetts 01003
Received 25 August 1997; accepted 20 October 1997
We have performed kinetic Monte Carlo KMC simulations of benzene tracer diffusion in NaY
for various loadings and temperatures to test the analytical diffusion theory presented in Paper I of
this series. Our theory and simulations assume that benzene molecules jump among SII and W sites,
located near Na ions in 6rings and in 12ring windows, respectively. Our diffusion theory is based
on a mean field approximation MFA which yields D 1
6k a2
, where a 11 Å is the mean
intercage jump length and 1/k is the mean supercage residence time. KMC simulations of D( ),
k , and a at 300 and 400 K show that our MFA is essentially exact for loadings that allow SII site
vacancies, and that the concentration dependence is controlled by k . For higher loadings, the MFA
error is independent of temperature, and increases roughly linearly with loading to a maximum
value of ca. 25%, resulting from correlated motion. We present an analytical theory for such
