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Transformation of AlPO-53 to JDF-2 : reversible dehydration of a templated aluminophosphate studied by MAS NMR and diffraction
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Ashbrook, Sharon E., Cutajar, Marica, Griffin, J. M. (John M.), Lethbridge, Zoe A. D., Walton, Richard I. and Wimperis, Stephen (2009) Transformation of AlPO-53 to JDF-2 : reversible dehydration of a templated aluminophosphate studied by MAS NMR and diffraction. Journal of Physical Chemistry C, Vol.113 (No.24). pp. 10780-10789. doi:10.1021/jp902074s
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Official URL: http://dx.doi.org/10.1021/jp902074s
Abstract
We describe a detailed study of the aluminum phosphate AlPO-53 in both its as-made and calcined forms. In its as-made state, AlPO-53(A), the material is templated by methylammonium cations and contains occluded water molecules and also hydroxide ions that bridge pairs of aluminum atoms, increasing their coordination number to 5. Solid-state NMR experiments confirm the local environment of the aluminum and phosphorus atoms proposed in a previous structural model from powder X-ray diffraction. P-31 NMR shows the presence of four distinct resonances with an intensity ratio of 1: 1:2:2, consistent with the expected six crystallographic p Sites. Al-27 triple-quantum MAS NMR resolves five aluminum peaks, two with NMR parameters characteristic of four-coordinate Al and three of five-coordinate Al. One of these latter signals has a greater intensity than that of the others, consistent with the presence of two overlapping signals from two distinct crystallographic Al sites. First-principles calculations of NMR parameters provide a complete spectral assignment and confirm our interpretation of unresolved spectra. AlPO-53(A) is found to convert easily into a second crystalline phase on moderate heating (upon spinning in the NMR rotor for an extended period, for example), and variable-temperature powder X-ray experiments, together with TGA, suggest that this is a dehydration process yielding a second aluminophosphate, JDF-2. This is confirmed using both P-31 and Al-27 NMR, with the spectral assignment of JDF-2 supported by first-principles calculations. Calcination of AlPO-53(A) or of the dehydrated material, JDF-2, at 300 degrees C yields the microporous open-framework material AlPO-53(B), a tetrahedral network with three Al and three P sites, as confirmed by NMR and first-principles calculations. In addition to demonstrating the power of the combined use of NMR, first-principles calculations, and diffraction for detailed structural investigations, we show that the possibility of a reversible dehydration in as-made AlPO-53 and similar systems is an important consideration in structural studies and provides evidence that the published structural model for AlPO-53(A) may be incomplete.
| Item Type: | Journal Article | ||||
|---|---|---|---|---|---|
| Subjects: | Q Science > QD Chemistry | ||||
| Divisions: | Faculty of Science > Chemistry | ||||
| Library of Congress Subject Headings (LCSH): | Phosphates, Aluminum, Nuclear magnetic resonance, X-rays -- Diffraction, Solid state chemistry | ||||
| Journal or Publication Title: | Journal of Physical Chemistry C | ||||
| Publisher: | American Chemical Society | ||||
| ISSN: | 1932-7447 | ||||
| Official Date: | 18 June 2009 | ||||
| Dates: |
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| Volume: | Vol.113 | ||||
| Number: | No.24 | ||||
| Number of Pages: | 10 | ||||
| Page Range: | pp. 10780-10789 | ||||
| DOI: | 10.1021/jp902074s | ||||
| Status: | Peer Reviewed | ||||
| Publication Status: | Published | ||||
| Access rights to Published version: | Restricted or Subscription Access | ||||
| Funder: | Research Councils UK (RCUK), Engineering and Physical Sciences Research Council (EPSRC), eDIKT | ||||
| Grant number: | EP/E041825 (EPSRC), GR/S96579 (EPSRC), EP/C516591 (EPSRC) |
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