Isolation and characterization of a novel lamellar-type aluminophosphate, AlPO4-L, a common precursor for AlPO4 molecular sieves

Abstract

Several aluminophosphate molecular sieves (AlPO4-5, AlPO4-22, AlPO4-16 and SAPO-35) are formed via a common lamellar aluminophosphate material (AlPO4-L) during hydrothermal synthesis from a gel containing Al2O3, P2O5, SiO2 and hexamethyleneimine (HEM) in aqueous (H2O), or non-aqueous (ethyleneglycol, EG) media. Depending on the concentration of the template HEM, AlPO4-L transforms into AlPO4-5, AlPO4-16 and AlPO4-22, while SAPO-L transforms into SAPO-35. AlPO4-L was isolated in a pure form from H2O as well as EG media and characterized by PXRD, SEM, TG/DTA, TG/MS and FTIR spectroscopic techniques. It is a lamellar aluminophosphate, intercalating HEM and H2O, and is thermally stable up to 250°C. AlPO4-L is believed to form by the rearrangement of macroanionic [3HEMH]3+Al3P4O3− 16 sheets formed in the reaction medium.