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

Abstract

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.

A study of molybdenum behaviour in UO2 by X-ray absorption spectroscopy

“…Furthermore, Aritani et al [25], who obtained the same values, showed that the reduction of molybdenum from +VI to +IV, causes a shrinking of the energy levels. However, as it also implies a lowering of the edge, the difference between a reduction and a modification of symmetry can be made.…”

“…Thus, if such a uranium molybdate appears, two components in the white line are expected. The first should be located at 2526.0 eV and the second at an energy gap of about 3 eV as described by Aritani et al [25]. Consequently, it appears impossible to differentiate the formation of a Whatever the hypothesis considered, the result obtained for the sample as implanted clearly shows that the peak located at 2523.8 eV corresponds to a presence of Mo atoms in the matrix grains.…”

“…In the case of the octahedral symmetry observed in MoO 2 and MoO 3 , one can speak about the orbital t 2g and e à g , while in the case of tetrahedral symmetry, as in MgMoO 4 , one can speak about the orbital e g and t à 2 [25]. The relative intensity of the two components of the white lines is a function of the transition probability (t 2g /e à g ¼ 2/3 and e g /t à 2 ¼ 3/2).…”

In situx-ray-absorption spectroscopy study of hydrogen absorption by nickel-magnesium thin films

“…The Mg K-edge spectra shifted towards higher energy by ~2.2 and ~2.9 eV for Ni 0. 33 Mg 0.67 and Ni 0. 13 Mg 0.87 , respectively, when hydrogen is introduced.…”

From Yellow to Black: Dramatic Changes between Cerium(IV) and Plutonium(IV) Molybdates

“…[65][66][67][68][69][70][71][72][73] However, the energy at the 1/2-height of the edge is better, and indicates something close to Mo(VI), since Mo(IV) ½-height energies are typically below 20011 eV when using our chosen energy calibration. 63,64 With such uncertainty, it is not really possible to determine how much Mo(V) is mixed in; we therefore report here that the Mo K-edge XANES are consistent with a Mo(V,VI) state.…”