The Mechanism of Phase Transition of Molecular Sieve VPI-5 into AlPO_4-8

The aluminophosphate molecular sieve VPI-5 has received much attention as a new structure containing one-dimensional circular pores circumscribed by 18 tetrahedral atoms. The AlPO;-8 is another new type of structure which was found to contain 1 4-ring open pores. Recently, we have successfully synthesized the molecular sieves of VPI-5 and AlPO;-8, and found that the mixture of VPI-5 and AlPO;-8 was easily formed under similar conditions, and VPI-5 can be converted to AlPO;-8 by dehydration via heating. It is suggested that there exists relationship between the structures of VPI-5 and A1PO;-8. Therefore, the study on the transition and relationship between VPI-5 and A1PO;-8 is very important for designing and preparing new molecular sieves with new structures.