Mobility of adsorbed species in zeolites: a molecular dynamics simulation of xenon in silicalite

Results from a molecular dynamics simulation of xenon in silicalite at 298 K and 4 atoms per unit cell (A&, = -26.9kJ/mol, D = 1.86 X m2/s) are in good agreement with the experimental value of -24.5 kJ/mol and the diffusion coefficient derived from the NMR pulsed field-gradient method (4.00 X m2/s).The diffusivity is predicted to be negligible at temperatures around 77 K and then increases over the investigated range to D = 3.25 X m2/s at 450 K, yielding an activation energy of 5.5 kJ/mol.Increasing the concentration from 4 to 16 atoms per unit cell results in a decreased internal energy of adsorption (-28.1 kJ/mol) and a decreased diffusion coefficient (D = 0.37 X lo4 m2/s).The anisotropy of diffusion is also examined.