Abstract

In framework aluminosilicate materials (e.g., feldspars, zeolites and many others), it is generally assumed that AlO 4 tetrahedra do not share corners, i.e., that Al-O-Al oxygen sites are avoided when stoichiometry permits. This assumption plays a key role in models of thermodynamic properties and of reaction kinetics. We present a new approach to directly test this assumption, based on 17 O triple-quantum magic-angle spinning nuclear magnetic resonance (3QMAS NMR). We show that thermodynamically significant concentrations of Al-O-Al sites can be observed in a naturally occurring zeolite (stilbite), and that these sites react faster with H 2 O vapor than do Si-O-Si and Si-O-Al sites.

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