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

Several aluminophosphate molecular sieves (AlPO(4)-5, AlPO(4)-22,;AlPO(4)-16 and SAPO-35) are formed via a common lamellar aluminophosphate material (AlPO(4)-L) during hydrothermal synthesis from a gel containing Al(2)O(3), P(2)O(5), SiO(2) and hexamethyleneimine (HEM) in aqueous (H(2)O), or non-aqueous (ethyleneglycol, EG) media. Depending on the concentration of the template HEM, AlPO(4)-L transforms into AlPO(4)-5, AlPO(4)-16 and AlPO(4)-22, while SAPO-L transforms into SAPO-35. AlPO(4)-L was isolated in a pure form from H(2)O 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 H(2)O, and is thermally stable up to 250 degrees C. AlPO(4)-L is believed to form by the rearrangement of macroanionic [3HEMH](3+) Al(3)P(4)O(16)(3-) sheets formed in the reaction medium. (C) 1998 Elsevier Science B.V. All rights reserved.