Molecular Motion of Hydrogen-Bonded CH < inf> 3 CN in H-MFI: A < sup> 1 H, < sup> 2 H, and < sup> 13 C Multinuclear Nuclear Magnetic Resonance Study

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The dynamics associated with the adsorption complex formed by CH3CN at Brønsted sites in the high-silica zeolite H-MFI have been explored using 1H, 2H, and 13C nuclear magnetic resonance (NMR) spectra measured as a function of temperature between 78 and 400 K. A simple NMR line-shape theory, based on rapid, small-angle reorientations of the CH3CN molecular axis with a temperature-dependent amplitude, has been used to account for the data. An anisotropic, angular motion is observed with a small amplitude at low temperatures increasing to approximately ±35 ° from its average position at room temperature. This motion is primarily constrained to a plane in the zeolite, but a distribution in amplitudes for different types of sites is required to fully account for the data. At higher temperatures, the powder line shapes are completely motionally narrowed, presumably due to exchange between physisorbed molecules and those bound to the sites.

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Journal of Physical Chemistry B