Synthesis of AIPO4-11

Both electronic and steric effects influence the synthesis of AIPO4-11. Successful syntheses involve the use of secondary amines having lengths comparable to the unit cell c-dimension of AIPO4-11 (i.e., ca. 8.4 Å). Bayerite [AI(OH)3] and pseudoboehmite (AIOOH) provide the most suitable reagent sources of aluminium, and phosphorus is preferably obtained from H3PO4. It is also preferable to avoid large concentrations of cations other than protons or protonated amines. A 90°C, pretreatment of the AIPO4 gel produces poorly crystalline AIPO4·2H2O (i.e., metavariscite/variscite), which reacts on subsequent heating at higher temperatures with concomitant formation of microporous AIPO4 products. This suggests that the AIPO4·2H2O is a reactive intermediate. The formation of this intermediate seems to enhance the production of AIPO4-11 over condensed-phase AIPO4's. Substitution of atoms into this intermediate may be the critical step in determining the levels of substitution into the framework of substituted AIPO4's.