SOLID-STATE TRANSFORMATION OF SAPO-37 MOLECULAR-SIEVE ABOVE 1100-K

The changes occurring in SAPO-37 upon heating it to 1273 K are studied using Si-29, Al-27 and P-31 magic-angle-spinning nuclear magnetic res onance (MAS NMR), X-ray diffraction (XRD) and infrared spectroscopy. T he removal of the template at 873 K leads to a shift of both Si-29 and Al-27 MAS NMR peaks, suggesting an interaction of the template with s ome SiO4 and AlO4 tetrahedra. A further solid-state transformation is shown to occur between 1073 and 1173 K. This involves the formation of siliceous islands, generating silicoaluminate domains. The faujasite crystal structure is maintained. At 1273 K the material is fully trans formed to a mixture of tridymite and cristobalite structures. A model is proposed for the migration of atoms in the framework.