Dynamic properties of p-xylene adsorbed on Na-ZSM-5 zeolite by deuterium and proton magic-angle sample spinning NMR

Solid-state deuterium and proton magic-angle sample spinning (MASS) NMR measurements as function of temperature, on two deuteriated p-xylene species, CH/sub 3/C/sub 6/D/sub 4/CH/sub 3/ and CD/sub 3/C/sub 6/H/sub 4/CD/sub 3/, sorbed in Na-ZSM-5 zeolite are presented. The results are interpreted in terms of possible dynamic state and sorption sites of the sorbed molecules. Altogether five species are identified, whose relative abundances vary with the loading level and the temperature of the sample. The various species differ in the dynamic state of the phenyl ring and the molecular axis, but in all of them, at least down to /approximately/-150/degrees/C, there is fast reorientation of the methyl groups. The five dynamic states are (1) static molecules, (2 and 3) molecules whose phenyl rings undergo, respectively, dicrete 180/degrees/ flips and free continuous rotation about their para axis, and (4 and 5) molecules whose molecular axes exhibit twofold jumps through 90/degrees/ and 112/degrees/, respectively. The various species can be attributed to (1) rigidly sorbed molecules in the zeolite channels, (2 and 3) molecules that undergo local reorientations about their para axis, and (4 and 5) molecules sorbed near intersections between channels and undergoing two-site jumps between neighboring segments of the straight and zigzag channels or between neighboring zigzag segments.