The qualitative dependence on cavity size of 129Xe NMR chemical shifts for xenon sorbed in zeolites was usually interpreted in terms of collisions between xenon and cavity walls. Molecular dynamics simulation at infinite dilution was a powerful tool to give insight into the collision effect. The contact time and the number of collisions with oxygen atoms of the framework were deduced from molecular dynamics calculations in pure siliceous zeolites of various cavity size (Y zeolite, silicalite, and mordenite) at different temperatures. Correlation between chemical shifts and the number of binary collisions was found. The occurrence of two signals in mordenite spectra cannot be interpreted by the model of pure siliceous framework. It was assumed a certain number of side pockets were blocked, possibly by cations. The ratio of accessible pockets, derived from NMR spectra, increased with temperature from 0.015 to 12% in Na mordenite. The diffusion coefficient with the blockage of the pockets taken into account was determined to be 4.3 x 10-9m2/s at 300K.

Analysis of 129Xe Chemical Shifts in Zeolites from Molecular Dynamics Calculations. F.Vigné-Maeder: Journal of Physical Chemistry, 1994, 98[17], 4666-72