Solid-state transformation of SAPO-37 molecular sieve above 1100 K

Abstract

The changes occurring in SAPO-37 upon heating it to 1273 K are studied using ²⁹Si, ²⁷Al and ³¹P magic-angle-spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction (XRD) and infrared spectroscopy. The removal of the template at 873 K leads to a shift of both ²⁹Si and ²⁷Al MAS NMR peaks, suggesting an interaction of the template with some 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 transformed to a mixture of tridymite and cristobalite structures. A model is proposed for the migration of atoms in the framework.