On the thermal degradation of 3-methylaminopropylamine captured inside the aluminum phosphate analog of ULM-3

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 (27)Al, (31)P, and (19)F MAS NMR spectroscopy. The MAPA, located in the ten-membered ring channels, is doubly protonated to balance the negative charge of the Al(3)P(3)O(12)F(2) (2-) 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-HaEuro broken vertical bar 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.