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  • 1 Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, 11000 Serbia
  • 2 National Institute of Chemistry, Hajdrihova 19, Ljubljana, 1000 Slovenia
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Abstract  

An open-framework aluminophosphate analog of the fluorogallophosphate structure-type ULM-3 was obtained by hydrothermal crystallization of an aqueous aluminum phosphate suspension in the presence of 3-methylpropylamine (MAPA) and hydrofluoric acid. The open-framework fluorinated aluminophosphate structure was confirmed by Rietveld analysis and the 27Al, 31P, and 19F MAS NMR spectroscopy. The MAPA, located in the ten-membered ring channels, is doubly protonated to balance the negative charge of the Al3P3O12F22– framework. Thermogravimetric analysis data have been used to study kinetics of the thermal decomposition of MAPA. The decomposition was found to be a complex process, its activation energy varied from 177 to 259 kJ mol−1. The relatively high E values are explained by the fact that the MAPA cations are bound to the anionic framework both by electrostatic forces as well as strong N-H…O hydrogen bonds. The strength of the interactions is indirectly confirmed by the in situ high temperature X-ray diffraction analysis which shows that the MAPA decomposition leads to a phase transformation of the open-framework structure to the dense trydimite phase.