The diffusion coefficients and activation energies of benzene in siliceous faujasite (D298 = 4.5 x 10-10m2/s, E = 10.2kJ/mol) and Na-Y (D298 = 3.6 x 10-12m2/s E = 23.5kJ/mol) were determined using 2H NMR spin-lattice relaxation methods. Unlike Na-Y, where benzene bonded to SII cations, no specific adsorption site was observed in the siliceous analogue; as reflected in significantly higher diffusion coefficients and lower activation energy. Molecular dynamics simulations of benzene adsorbed in siliceous Y zeolite (D298 = 2.0 x 10-9m2/s) were in good agreement with the experiment, and from the trajectories it could be seen that the sorbate maintains close interactions with the walls of the supercage. On the 25ps time scale of the MD simulation, the behavior of benzene was largely dominated by intracavity rather than intercavity motion. For the slower diffusion of benzene in Na-Y, trajectories over a period of ≫1ns would be needed to observe intercavity motion.

Behavior of Benzene in Siliceous Faujasite: a Comparative Study by 2H NMR and Molecular Dynamics. L.M.Bull, N.J.Henson, A.K.Cheetham, J.M.Newsam, S.J.Heyes: Journal of Physical Chemistry, 1993, 97[45], 11776-80