Structure of Mo−Mg Binary Oxides in Oxidized/Reduced States Studied by X-ray Absorption Spectroscopy at the Mo K Edge and Mg K Edge

The local structure around Mo atoms in Mo−Mg binary oxides has been investigated by X-ray absorption spectroscopy at Mo and Mg K edges. XANES and EXAFS spectra show that the binary oxides have a tetrahedral MoO 4 unit in the samples with a Mo/(Mo + Mg) ratio of less than 0.5 and an octahedral MoO 6 unit in the samples with a higher ratio. By H 2 treatment at 773 K, a molybdena-rich binary oxide was easily reduced to form the MoO 2 phase, which was not detected by XRD but was by EXAFS. It is concluded that the reduced oxide contains low valent Mo ions in the MoO 2 phase and the ions work as an active center for propene metathesis.