Abstract
The surface preparation-dependent interactions of ammonia with ..gamma..-alumina were explored via solid-state /sup 15/N and /sup 2/H NMR spectroscopies. /sup 15/N experiments demonstrated an unresolved distribution of ammonia surface species. Wide-line /sup 2/H line shapes and T/sub 1/ experiments indicate the presence of three motionally distinct deuteron resonances associated with the ammonia adsorbate. An ammonia resonance indicative of rapid motion about the threefold symmetry axis was isolated for the more sparsely hydrated surfaces and has been identified as the Lewis complex resonance. T/sub 1/ experiments show for this site that motion about the threefold axis is diffusive. A second deuterium resonance has been identified as a surface hydroxyl species by comparison with D/sub 2/O on ..gamma..-alumina experiments. This resonance shows a direct proportion of intensity with surface hydroxyl concentration, demonstrating the exchange of Broensted hydrogens with ammonia hydrogen atoms. A third component of the deuterium line shapes has been associated with surface Broensted ammonium species and appears to be comprised of a distribution of motionally averaged species. The experimental line shapes were simulated, and the relative Lewis and Broensted site populations of ammonia were estimated.
Published Version
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