Thermal analyses of various alkylamines-templated aluminophosphate AlPO₄-21

Thermal removals of amine-templated aluminophosphate molecular sieve AlPO₄-21 have been studied by X-ray powder diffraction (XRD), TG-DTA and temperature-programmed decomposition coupled with mass spectrometer (TPD-MS) analyses (amine: ethylamine, dimethylamine and trimethylamine). It is found that the thermal removal of templates and bridging OH groups between two Al atoms is an endothermic process occurring in a single step in inert atmosphere, which accompanies the structural transformation of AlPO₄-21 to AlPO₄-25. The removal temperatures of various organic amines occluded within AlPO₄-21 are directly related to the shapes and sizes of the templates, as well as the proton affinities of guest cations. These factors also determine the removal mechanisms of templates from AlPO ₄-21.