SOLID-STATE NMR AND XRD STUDY OF THE THERMAL-STABILITY OF THE MOLECULAR-SIEVE VPI-5 - CONDITIONS FOR THE TRANSFORMATION PROCESS

The thermal stability of VPI-5 and the conditions for the transformation of VPI-5 to AlPO4-8 have been investigated by X-ray diffraction and in situ variable-temperature Al-27 and P-31 MAS NMR. These results indicate that under normal open air drying conditions, VPI-5 transforms irreversibly to AlPO4-8 within 60 min at temperatures greater-than-or-equal-to 70-degrees-C. In contrast, under sealed conditions with the restricted loss of water, the VPI-5 structure is maintained to > 150-degrees-C. However, careful low-temperature dehydration in vacuo allows the structure to be preserved even after heating to 400-degrees-C.