th  - 1987 - 51st ENC Conference

WF8
MULTIPLE ~ANTUH AND 129XE NMR STUDIES OF THE DISTRIBUTION OF MOLECULES
IN A ZEOLITE •
R. Ryoo, S.-B. Liu, L. C. de Menorval, and A. Pines
University of California, Berkeley
Proton multlple-quantum (MQ) NMR measurements and analyses of 129Xe
NMR spectra were used to probe the spatial distrlbutlon of simple
molecules adsorbed in molecular sleves. The behavior of homogeneously
chemlsorbed hexamethylbenzene (HMB) In the supercages of Na-Y zeolite is
demonstrated. Distinct chemlcal shift llnes were observed from 129Xe
NMR spectra of adsorbed xenon on Na-Y zeolite samples with different wt%
of ehemisorbed HMB molecules. In the absence of HMB chemisorbed in the
sample, a single llne at - 90 ppm due to xenon (300 Tort) In zeolite
supercages Is obtained. When, on the average, each zeolite supercage is
occupied by one HMB molecule, a single line occurs at different chemical
shift values (- 120 ppm). In the intermediate case, when only a portion
of the supercages are occupied by the HMB molecule, both llnes are
present corresponding to the two cases above.
The clusterlng of HMB molecules In zeollte supercages has been
confirmed by proton MQ NMR measurements. For samples below - 12 wig HMB
In Na-Y zeolite, HQ NMR data glve conslstant results indicating that
only up to one HMB molecule per zeolite supercage can occur. Thls Js In
accord wlth the observations from 129Xe spectra.
These techniques have proven to be useful in the first step toward
understanding the behavior of molecules under restricted dimension.
*R. Ryoo, S.-B. L1u, L.C. de Henorva], J. Fralssard and A. Pines. to be
publlshed.