Jonathan F. Stebbins, Peidong Zhao, Sung Keun Lee, Xing Cheng; Reactive Al-O-Al sites in a natural zeolite; triple-quantum oxygen-17 nuclear magnetic resonance. American Mineralogist ; 84 (10): 1680–1684. doi: https://doi.org/10.2138/am-1999-1023
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.