TY - JOUR

T1 - A multinuclear solid-state NMR study of templated and calcined chabazite-type GaPO-34

AU - Amri, Mahrez

AU - Ashbrook, Sharon E.

AU - Dawson, Daniel M.

AU - Griffin, John M.

AU - Walton, Richard I.

AU - Wimperis, Stephen

PY - 2012/7/19

Y1 - 2012/7/19

N2 - 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.

AB - 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.

KW - NEGATIVE THERMAL-EXPANSION

KW - GALLOPHOSPHATE MOLECULAR-SIEVE

KW - BROMIDE IONIC LIQUIDS

KW - MAS NMR

KW - IONOTHERMAL SYNTHESIS

KW - GALLIUM PHOSPHATE

KW - MICROPOROUS ALUMINOPHOSPHATES

KW - 1ST-PRINCIPLES CALCULATIONS

KW - QUADRUPOLAR NUCLEI

KW - CRYSTAL-STRUCTURE

U2 - 10.1021/jp304868w

DO - 10.1021/jp304868w

M3 - Journal article

VL - 116

SP - 15048

EP - 15057

JO - The Journal of Physical Chemistry C

JF - The Journal of Physical Chemistry C

SN - 1932-7447

IS - 28

ER -