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First-time applications of solid-state exchange 13C NMR techniques to the study of the reorientation dynamics of hydrocarbon molecules adsorbed on zeolites have enabled the geometry and time scales of molecular hopping processes between adjacent adsorption sites to be characterized directly and model free. Two-dimensional exchange 13C NMR on static samples establishes the geometry of the site-hopping dynamics, while one-dimensional magic-angle spinning (MAS) exchange-induced-sidebands (EIS) 13C NMR permits motional correlation times on the order of milliseconds to seconds to be extracted directly from the experimental data. Variable-temperature experiments performed on Ca-LSX zeolite samples with average bulk loadings of 0.5, 1, and 2 benzene molecules per supercage yield apparent Arrhenius activation energies of about 66 ± 6 kJ mol-1 for the discrete, localized reorientation dynamics of benzene molecules among different Ca2+ cation adsorption sites (∼0.5 nm apart). Arrhenius preexponential factors were established to be on the order of 1 × 1012 s-1, consistent with elementary hopping processes. Motional correlation times exhibit only minor variations upon changes in benzene loading over the range studied.

One-and two-dimensional 2 Hand 13 C-NMR ͑nuclear magnetic resonance͒ echo spectroscopy and 1 H static field gradient NMR self-diffusion experiments have been used to study the reorientational and translational dynamics of benzene molecules adsorbed on zeolite NaY as a function of loading. Comparison of the data with model calculations establish that the elementary motional process of the guest molecules is consistently identified as a jump process among well defined adsorption sites inside a supercage and/or a jump between nearby supercages. In cases where the zeolite cavities contain high loadings of guest molecules, each molecular jump is accompanied by concomitant relaxation of the local environment. Molecular jump events between adsorption sites correspond to the elementary processes from which long range translational diffusion evolves.

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