Molecular dynamics simulations were used to obtain a detailed understanding of the self-diffusion of methanol in NaY zeolite. A force-field term was derived with which to describe the interactions between methanol molecules and extra framework cations. Via the simulations, it was shown that diffusive behavior in the high-temperature range consisted of a combination of both short- and long-range motions at low and intermediate loadings. This type of motion was characterized by an activation energy that decreased as the loading increased. At low loadings, short-range diffusive behavior based upon a surface-mediated mechanism was also observed. The short-range behavior corresponded to motion only on the length-scale of an FAU super-cage, whereas the long-range behavior involved intercage diffusion. At saturation loading, corresponding to 96 methanol molecules per unit cell, only short-range motion within the same super-cage predominated.

Diffusion of Methanol in Zeolite NaY: a Molecular Dynamics Study. Plant, D.F., Maurin, G., Bell, R.G.: Journal of Physical Chemistry B, 2007, 111[11], 2836-44