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 AlPO4-21.