AL-27 AND SI-29 NMR-STUDIES OF HZSM-5 .1. THE EFFECT OF SORBED MOLECULES

Various sorbates on the zeolite HZSM-5 were studied by multinuclear n.m.r. 29Si relaxation was shown to be due to the presence of paramagnetic oxygen in the channel pores. Sorption of alkanes displaced oxygen and increased T1(Si); it also displaced water, which had a synergistic effect on steric interactions with the channel walls leading to an upfield shift in the 29Si spectrum. 27Al spectra were shown to be strongly influenced by the amount of sorbed water since there is an equilibrium between protonated aquo species and free water in the channels. Models for the interaction of the acidic proton with water and Al are discussed, and proton hopping from the species associated with Al to free water molecules is postulated. © 1990.