Structural Investigation by Multinuclear Solid State NMR and X-ray Diffraction of As-Synthesized, Dehydrated, and Calcined AlPO₄-SOD

Abstract

AlPO4-SOD, a microporous aluminophosphate, was synthesized in a quasi-nonaqueous medium using dimethylformamide as solvent and template. The as-synthesized, dehydrated, calcined materials and the corresponding rehydrated phases were investigated by various solid-state nuclear magnetic resonance (NMR) and powder X-ray diffraction techniques. Structural data from the NMR study are in a very good agreement with the as-synthesized AlPO4-SOD structure refined from powder synchrotron data. 31P homonuclear correlation and 31P/27Al 3QHETCOR experiments allowed the complete assignment of 31P and 27Al resonances to the corresponding crystallographic sites. 31P and 27Al NMR spectra are drastically modified after dehydration at 200 °C and calcination at 800 °C. A possible structural rearrangement of the template molecules is proposed that explains NMR and XRD data of the dehydrated material. The structure of the calcined material solved by powder XRD is in agreement with the NMR data.