Silicon distribution in SAPO materials:: A computational study of STA-7 combined to 29Si MAS NMR spectroscopy

The distribution of silicon atoms in the STA-7 framework has been investigated by combining Si-29 MAS NMR spectroscopy and computational tools based on energy minimization techniques. It was clearly established that only a SM2 silicon substitution mechanism occurs for an atomic silicon content of 0.05 and 0.10, generating preferential sites for silicon atoms in the large channels associated with protons pointing systematically towards the centre of the cavities interacting with a 6-membered ring. The modelling techniques are used to propose the most stable configurations for the STA-7 frameworks of varying silicon content. This procedure allows us to provide a realistic microscopic description of the STA-7 material, a key step before further investigation of the properties of this system. (C) 2007 Elsevier Inc. All rights reserved.