In Situ High Temperature High Pressure MAS NMR Study on the Crystallization of AlPO₄-5

A damped oscillating crystallization process of AlPO 4 -5 at the presence of small amount of water is demonstrated by in situ high temperature high pressure multinuclear MAS NMR. Crystalline AlPO 4 -5 is formed from an intermediate semicrystalline phase via continuous rearrangement of the local structure of amorphous precursor gel. Activated water catalyzes the rearrangement via repeatedly hydrolysis and condensation reaction. Strong interactions between organic template and inorganic species facilitate the ordered rearrangement. During the crystallization process, excess water, phosphate, and aluminums are expelled from the precursor. The oscillating crystallization reflects mass transportation between the solid and liquid phase during the crystallization process. This crystallization process is also applicable to AlPO 4 -5 crystallized in the presence of a relatively large amount of water.