Quantification of aluminium coordinations in alumina and silica–alumina by Al K-edge XANES

Abstract

The Al coordinations (AlO₄ tetrahedra and AlO₆ octahedra) in aluminium-containing oxides were successfully quantified by the curve fitting analysis of Al K-edge X-ray absorption near-edge structure (XANES). XANES spectra of aluminium-containing oxides showed three distinguishable peaks: one at 1566 eV assignable to tetrahedral AlO₄ and two at 1568 and 1572 eV characteristic of octahedral AlO₆. For the five reference oxides of well-known local structures, the ratio of the peak area at 1566 eV to that at 1568 eV estimated by curve fitting analysis agreed well with the known ratio of AlO₄ to AlO₆ species, when mixed Gaussian–Lorentzian functions were employed. This method was applied to quantify the variations of Al coordinations in transition alumina with the calcination temperature and in silica–alumina with the Al content.