1 2 9Xe nuclear magnetic resonance studies of xenon in zeolite CaA

Abstract

The average 129Xe nuclear magnetic resonance (NMR) chemical shift for xenon atoms in alpha cages of zeolite CaA is observed in a single peak dependent on xenon loading (〈n〉=0.5–8.9 Xe atoms/alpha cage) and temperature (240–360 K). The general increase of the shift with increasing average number of xenon atoms per alpha cage is shown to be due largely to the changing distribution of occupancies with increasing 〈n〉, coupled with increasing increments in the chemical shifts of Xen with increasing n. Except at the highest loadings, the results obtained for xenon in CaA are predicted nicely on the basis of δav(T)=(1/〈n〉)Σnnδn(T)Pn (〈n〉,T), where the fractions Pn of alpha cages containing n Xe atoms are imported from the Pn measured in xenon in zeolite NaA. The high loading data in CaA are interpreted in terms of contributions to the average 129Xe chemical shifts associated with xenon atoms in the window positions.