Adsorptive properties and stability of VPI-5, a large-pore molecular sieve

Abstract

The unusual adsorptive properties and the reported instability of VPI-5 have been investigated in some detail. The VPI-5 framework was found to undergo an irreversible but incomplete phase transformation to AlPO₄-8 during the removal of the zeolitic water. Furthermore, ill-defined constrictions are believed to be introduced into the framework during the course of this transformation. These have a great effect on the resulting adsorptive properties of dehydrated VPI-5. The adsorptive properties of the dehydrated material are dependent on factors such as the outgassing conditions, the sample history, the concentration of intracrystalline P—OH and other defect sites and the method of sample synthesis.