 
Summary: Diffusion in zeolites via cagetocage kinetics: Modeling benzene diffusion
in NaY
Scott M. Auerbacha)
Departments of Chemistry and Chemical Engineering, University of Massachusetts, Amherst,
Massachusetts 01003
Horia I. Metiu
Departments of Chemistry and Physics, University of California, Santa Barbara, California 93106
Received 1 March 1996; accepted 24 May 1996
We have performed kinetic Monte Carlo simulations of benzene diffusion in NaY Si:Al 2.0 over
the temperature range 200500 K. For hopping on a tetrahedral lattice, we derive the analytical
formula for D in terms of hopping lengths and times, yielding the simplecubic relation D 1
6ka2
,
even though the lattice is very different from simple cubic. We have calculated the distribution of
cage residence times for benzene in NaY, finding single exponential decay controlled by the
SIIW rate coefficient, even though several processes contribute to intercage motion. Exact
agreement between mean square displacement slopes and 1
6ka2
is obtained only when using kinetic
intercage hopping lengths, which are found to be in excess of the static length by as much as 0.54
