XE-129 NMR-STUDY OF Y3+-EXCHANGED, LA3+-EXCHANGED, AND CE3+-EXCHANGED X-ZEOLITES

The Xe-129 n.m.r. spectrum of adsorbed xenon has been used to locate the Y3+, Ce3+, and La3+ ions that are exchanged into NaX zeolite. The chemical shift of xenon adsorbed on yttrium-X zeolite follows a concave plot against the adsorbed xenon concentration, very similar to the previous Xe-129 n.m.r. study of Mg2+, Ca2+, and Ni2+ in Y zeolites. This result suggests strong adsorption of xenon on the Y3+ ion located inside the zeolite supercage. In contrast, the Xe-129 n.m.r. chemical shift for the CeX and LaX zeolites indicates that the cations are located in hexagonal prisms or sodalite cages inaccessible to the xenon atoms. The example of the Y3+ cation proves that not all trivalent cations migrate outside the supercages during thermal treatment of the solid.