129Xe NMR chemical shifts and linewidths of xenon in zeolites ZnY. Part 2.—Examination of various origins of chemical shift distributions

Abstract

A general procedure for calculating ¹²⁹Xe NMR line shapes and widths based on a well established multi-site adsorption model is presented. Assuming the chemical shift distribution arises primarily from macroscopic inhomogeneities of supercage cation concentrations at the crystallographic positions SIII and SII, ¹²⁹Xe NMR linewidths and their pressure dependences are calculated for the example of a 74% zinc-exchanged zeolite NaY. The agreement with experimental data is satisfactory at high pressures. However, an additional distribution of the local isotropic chemical shifts has to be taken into account in order to achieve an improved agreement of calculated and experimental data in the low pressure region.