Molecular dynamics simulations were made of individual trajectories, that were started in the transition state for cage-to-cage diffusion, for benzene and p-xylene in zeolite NaY. Diffusion coefficients and activation energies were

deduced from a hopping model that considered dynamic corrections. The transmission coefficients for both molecules were small; particularly at low temperatures. The influence of the window adsorption site of benzene upon the transmission coefficient was investigated. The hopping model failed for the treatment of benzene diffusion at temperatures greater than 700K (table 54) because diffusion could not be divided into different jump events at those temperatures. The results for p-xylene diffusion were in very good agreement with experimental results. For benzene, the activation energy results were slightly too high. This was attributed to the possible dependence of activation energy upon the exact positions of the sodium ions.

Diffusion of Aromatic Molecules in Zeolite NaY. 2. Dynamical Corrections. T.Mosell, G.Schrimpf, J.Brickmann: Journal of Physical Chemistry B, 1997, 101[46], 9485–94

Table 54

Calculated Diffusion Coefficients for NaY Zeolite