Further Studies on Aluminophosphate Molecular Sieves Part 2.-VPI-5 and Related Aluminophosphate Materials

VPI-5 and AIPO,-H2 are constructed from t h e same type of chain building uni t which contains octahedral Al atoms (coordinated with four framework oxygens and two water molecules). The bonded water molecules are believed to stabilize the cha in building unit and play an important role in the crystallization of these materials. This chain building unit limits the possibilities of incorporating silicon into t h e VPI-5 framework and synthesizing aluminosilicate or pure-silica versions of t h e VPI-5 structure. VPI-5 and AIPO,-H2 can irreversibly transform to AIPO,-8 and AIP0,-tridymite, respectively, via similar bond rearrangements. Several new aluminophosphates with X-ray powder diffraction reflections similar to some of those for VPI-5 are synthesized and their physicochemical properties do not match those for VPI-5. Strong evidence is provided to suggest that previous claims that VPI-5 and AIP0,-H1 are the same phase are unwarranted.