Structural study of Na8[AlSiO4]6(CO3)x(HCOO)2−2x(H2O)4x, 0.2≤x≤1, synthesized in organic solvents: order and disorder of carbonate and formate anions in sodalite

Abstract

Structural differences between sodalite “as-synthesized” in the system NaOCH3–2SiO2–Al2O3–Na2CO3–(CH3OH) and the calcined product were investigated. The characterization of the sodalites was carried out by X-ray powder diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy, as well as by 29Si and 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and 23Na satellite transition (SATRAS) NMR spectroscopy. Reaction products of the solvent/base were identified by {1H}13C cross-polarization MAS NMR and 1H MAS NMR. It can be shown that formate results from solvent–base reactions and is enclathrated in the β cages of the sodalite besides carbonate. Calcination at 773 K gives rise to the conversion of formate to carbonate, carbon dioxide and water, which leads to a total ordering of carbonate in the sodalite matrix. Rietveld structure refinements, thermal analysis and high-temperature 23Na and 1H MAS NMR studies confirm this behavior of the templates.