Meso and microporous solids

In view of the chemistry of this inert element, the main application of Xe NMR is as a surface probe for studying meso and microporous solids and the free volume in polymers. The relaxation time for Xe adsorbed in solids is typically 10 ms to a few seconds. The use of Xe NMR as a probe for studying microporous solids has been extensively reviewed by Barrie and Klinowski (1992). A more recent example of the use of Xe NMR to study surface interactions is provided by a study of borosilicalites with the ZSM-5 structure (Ngokoli-Kekele et al. 1998). The Xe shift of adsorbed xenon (referred to the shift of the pure gas extrapolated to zero pressure) was found to change regularly with boron content, with a discontinuity at a boron content of about one atom per unit cell ascribed to a change in the distribution of boron atoms in the lattice. A similar correlation between the Xe NMR shift and the aluminium content has been reported for the zeolite ZSM-5, in which the discontinuity occurred at about 2 Al atoms per unit cell (Chen et al. 1992). 

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