Research output: Contribution to Journal/Magazine › Journal article › peer-review
<mark>Journal publication date</mark> | 19/07/2012 |
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<mark>Journal</mark> | The Journal of Physical Chemistry C |
Issue number | 28 |
Volume | 116 |
Number of pages | 10 |
Pages (from-to) | 15048-15057 |
Publication Status | Published |
<mark>Original language</mark> | English |
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.