Benzene diffusion in Na-Y zeolite (Si:Al = 2.0) at 100 to 500K was modeled. The kinetic Monte Carlo random walk model was used, with activation energies derived from a zeolite-hydrocarbon potential energy surface. An Arrhenius fit yielded an apparent activation energy of 41kJ/mol, as compared with previously determined experimental values of 14 to 27kJ/mol. Minimum energy paths from the potential energy surface exhibited so-called cartwheel and skateboard hopping mechanisms for benzene in Na-Y. Analysis of the results suggested that activation energies from long length-scale diffusion measurements such as pulsed field gradient NMR, should be interpreted as site-to-window activation energies, whereas those from short length-scale experiments such as spin-lattice relaxation NMR, corresponded to intra-cage site-to-site activation energies.

Transport Theory for Cationic Zeolites: Diffusion of Benzene in Na-Y. S.M.Auerbach, N.J.Henson, A.K.Cheetham, H.I.Metiu: Journal of Physical Chemistry, 1995, 99[26], 10600-8