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Thermochemical Study of the Relative Stability of Dense and Microporous Aluminophosphate Frameworks

Hu, Yatao and Navrotsky, Alexandra and Chen, Cong-Yan and Davis, Mark E. (1995) Thermochemical Study of the Relative Stability of Dense and Microporous Aluminophosphate Frameworks. Chemistry of Materials, 7 (10). pp. 1816-1823. ISSN 0897-4756. doi:10.1021/cm00058a010.

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To understand why AlPO_4 exhibits the structural diversity observed, the relative stability of a series of dense and microporous AlPO_4 frameworks, e.g., berlinite, tridymite, cristobalite, AlPO_4-5, -8, -11, -42, and VPI-5, has been examined by the combination of DSC and high-temperature calorimetric experiments with molten lead borate (2PbO*B_2O_3) solvent at 979 K. The enthalpies of formation at 298 K, relative to berlinite (quartz structure), are the following (in kJ/mol): tridymite, 5.1 (1.4); cristobalite, 6.1 (1.2); AlPO_4-5, 14.0 (2.2); AlPO_4-8,113 (1.4); AlPO_4-11,12.4 (1.2); AlPO_4-42, 15.6 (1.9); and VPI-5, 16.7 (2.3). All microporous AlPO_4 frameworks are only 11-17 kJ/mol less stable in enthalpy than berlinite. The calcined and then fully rehydrated microporous AlPO_4's, AlPO_4•nH_2O, show a linear correlation between the degree of hydration (n) and their molar volume. The enthalpy of interaction of adsorbed water with the framework ranges from -11 to -30 kJ/mol of AlPO_4, or -10 to -13 kJ normalized per mole of water. Taking the enthalpy of interaction into account, many of these microporous frameworks are energetically comparable to or more stable than berlinite in an aqueous environment. This may imply that there is little or no energy barrier to the formation of microporous AlPO_4 frameworks and explain the structural diversity observed for AlPO_4. These results are compared to those of a previous study on microporous high-silica zeolites.

Item Type:Article
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Navrotsky, Alexandra0000-0002-3260-0364
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 1995 American Chemical Society. Received January 13, 1995. Revised Manuscript Received July 13, 1995. This work was supported by the State of New Jersey through its Innovative Partnership Grants Program. We thank Dr. H. Kessler of Laboratoire de Matériaux Minéraux, France, for providing the sample of AlPO_4-42, Dr. J. B. Higgins of Mobil Research and Development Co. for many discussions and comments, Dr. E. Vicenzi of Princeton University for help in electron microprobe analysis.
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New Jersey Innovative Partnership Grants ProgramUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20180507-141345550
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Official Citation:Thermochemical Study of the Relative Stability of Dense and Microporous Aluminophosphate Frameworks Yatao Hu, Alexandra Navrotsky, Cong-Yan Chen, and Mark E. Davis Chemistry of Materials 1995 7 (10), 1816-1823 DOI: 10.1021/cm00058a010
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86256
Deposited By: George Porter
Deposited On:07 May 2018 23:03
Last Modified:15 Nov 2021 20:36

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