A multinuclear solid-state NMR study of templated and calcined chabazite-type GaPO-34

Amri, Mahrez and Ashbrook, Sharon E. and Dawson, Daniel M. and Griffin, John M. and Walton, Richard I. and Wimperis, Stephen (2012) A multinuclear solid-state NMR study of templated and calcined chabazite-type GaPO-34. The Journal of Physical Chemistry C, 116 (28). pp. 15048-15057. ISSN 1932-7447

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The open-framework gallophosphate GaPO-34 is prepared with either 1-methylimidazole or pyridine as the structure-directing agent. C-13 and H-1 NMR spectra for these two variants of the as-made GaPO-34 are fully assigned, confirming the presence of the protonated amine and water within the pores of both materials. P-31 MAS NMR confirms the presence of three crystallographic P sites, while Ga-71 MAS and MQMAS NMR spectra reveal three crystallographic Ga sites: two tetrahedral and one six-coordinate. Simulations of Ga-69 MAS NMR spectra from these results are in good agreement with spectra acquired at B-0 = 20.0 T, and assignments are supported by first-principles calculations. F-19 MAS NMR proves the presence of Ga-bridging fluoride within the as-made materials, leading to the six-coordinate gallium. Calcination removes the organic species and fluoride, yielding a microporous chabazite-type GaPO4, containing one tetrahedral Ga site. Exposure to moist air yields calcined, rehydrated GaPO-34 containing four-, five-, and six-coordinate gallium. Upon heating this material, loss of crystallinity is observed by powder X-ray diffraction and NMR, with the latter revealing a range of P and Ga environments. The thermal instability of calcined, rehydrated GaPO-34 contrasts with the isomorphous aluminophosphate, showing that apparently analogous materials may have important differences in reactivity.

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Journal Article
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The Journal of Physical Chemistry C
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28 Sep 2015 11:05
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22 Nov 2022 02:16