Nitrogen-15 nuclear magnetic resonance spectroscopy of adsorbed molecules

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Abstract
Nitrogen-15 n.m.r. spectroscopy has been applied to the study of the interactions between solid surfaces and molecules adsorbed on them. Nitrogen-15 spectra of ammonia, trimethylamine, pyridine and acetonitrile molecules sorbed in various zeolites were measured at 9.12 MHz by means of the conventional Fourier-transform n.m.r. technique. In all measurements carried out, substances were employed which were enriched with nitrogen-15 nuclei (ca. 95 %). The resonance shifts depend strongly on the nature of adsorption sites which may occur in the zeolites (e.g. Na+ cations, Brönsted- and Lewis-acid sites). The results clearly reveal the advantage of nitrogen-15 n.m.r. investigations in characterizing acidic properties in comparison with the carbon-13 n.m.r. measurements performed until now on adsorbate–adsorbent systems and emphasize that nitrogen-15 spectroscopy may become a powerful tool for the study of surface phenomena.

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