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

Amri, M., Ashbrook, S.E., Dawson, D.M., Griffin, J.M., Walton, R.I. and Wimperis, S. (2012) A multinuclear solid-state NMR study of templated and calcined chabazite-type GaPO-34. Journal of Physical Chemistry C, 116(28), pp. 15048-15057. (doi: 10.1021/jp304868w)

Abstract

The open-framework gallophosphate GaPO-34 is prepared with either 1-methylimidazole or pyridine as the structure-directing agent. 13C and 1H 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. 31P MAS NMR confirms the presence of three crystallographic P sites, while 71Ga MAS and MQMAS NMR spectra reveal three crystallographic Ga sites: two tetrahedral and one six-coordinate. Simulations of 69Ga MAS NMR spectra from these results are in good agreement with spectra acquired at B0 = 20.0 T, and assignments are supported by first-principles calculations. 19F 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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Wimperis, Professor Stephen
• Authors: Amri, M., Ashbrook, S.E., Dawson, D.M., Griffin, J.M., Walton, R.I., and Wimperis, S.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Physical Chemistry C
• Publisher: American Chemical Society
• ISSN: 1932-7447
• Published Online: 25 June 2012