 
Summary: Analytical theory of benzene diffusion in NaY zeolite
Scott M. Auerbach
Departments of Chemistry and Chemical Engineering, University of Massachusetts, Amherst,
Massachusetts 01003
Received 16 October 1996; accepted 3 February 1997
We have developed an analytical expression for the diffusion coefficient of benzene in NaY at
infinite dilution in terms of fundamental rate coefficients, which has been confirmed by extensive
kinetic Monte Carlo simulations. This model assumes that benzene jumps among SII and W binding
sites, located near Na ions in 6rings and in 12ring windows, respectively. Our diffusion theory
is based on D 1
6ka2
where a 11 Å is the intercage length and k is the cagetocage rate
coefficient. We have determined that k k SIIW · 1
2·3 1 k WW /k WSII) , a finding that
has resolved discrepancies between theory and simulation and has suggested new interpretations of
benzene diffusion in NaY. When (T) k WW /k WSII) is between 0 and 1, the factor
3 1 (T) counts the number of thermally allowed target sites for cagetocage motion.
Alternatively, when (T) 1, benzene mobility is interpreted as interstitial diffusion, wherein k is
controlled by the probability of W site occupancy multiplied by the rate of WW jump processes.
This limit is expected to arise with benzene loadings of four molecules per supercage. © 1997
