Mo L3-edge XANES and diffuse reflectance UV−vis spectra have been recorded for structural studies of Mo−Mg binary oxides which catalyze metathesis reactions of olefins after pretreatment with H2 at 773 K. The XANES of reference compounds revealed that the local symmetry around the Mo ion as well as the valence state affects the spectral features. From the XANES of Mo−Mg binary oxides in oxidized/reduced states, it is concluded that MoO4 tetrahedra are the main component in the near-surface region for samples of x (Mo/(Mo + Mg)) ≤ 0.7 in the oxidized state. For samples in the reduced state, the tetrahedral species remain, but reduced Mo ions including MoO2 species are also formed, while the MoO2 phase is formed in the bulk phase at x = 0.5−0.8. In the latter samples, Mo ions are easily reduced by treatment with H2. The active species for metathesis reactions relates to formation of the MoO2 phase not only in the bulk but also in the near-surface region.

We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of a=6.844 Å, b=6.933 Å, c=9.339 Å, α =76.617 °, β =84.188 °, γ =74.510 ° and space group Pī. The crystal structure suggests the chemical formula CoMoO 4. 3/4H 2 O. The structure consists of MoO 4 tetrahedra and CoO 6 octahedra, confirming the earlier XANES investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-, β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO 6 and MoO n polyhedra similar to those of the hp-phase.

Hydrogen molybdenum bronzes, HxMoO3, of Type-I (x=0.21), Type-III (x=1.55), and Type-IV (x=1.90) were prepared by the Glemser’s method. Type-II (x=0.91) was obtained from Type-III by standing in air for 120 days. The bronzes with low hydrogen contents were stable, but those with high contents were not so stable. All these bronzes have been studied by X-ray diffraction, IR spectroscopy, and TG-DTA. Bronzes with high hydrogen contents were changed upon heating in air, successively, to those with low hydrogen contents by the evolution of H2.

We have explored several structure-inheriting solid-state reactions (SISSRs) under hydrothermal conditions for syntheses in the Co-Mo-O system. And we found an interesting hydrothermal SISSR from CoMoO 4. 3/4H 2 O to high-pressure (hp-) phase of CoMoO 4 , which enabled us to considerably reduce the severe conditions for the synthesis of hp-CoMoO 4 . As similar hydrothermal SISSRs are expected to be useful tools for material syntheses, we also briefly discuss them as a means of developing novel material syntheses and designs.

NMR and DTA studies were carried out on four phases of hydrogen molybdenum bronzes, types I-IV. From DTA and X-ray data it is confirmed that the bronze with the highest hydrogen content changes successively to that with lowest hydrogen content and finally to MOO,, by evolution of H, . NMR spectra of types Il-IV obtained in the present study can be clearly resolved into three components, a Pake doublet, a Gaussian and a Lorentzian, which are attributed to paired protons, isolated protons fixed on a site, and moving protons, respectively. The phase changes of the bronzes are discussed by connecting them with hydrogen insertion. A preliminary result of computer-simulation analyses of the lineshapes is also given.

The hexagonal hydrate (I) of molybdenum trioxide, which has been newly found and reported, was studied by X-ray diffraction analysis, IR and NMR spectroscopies, and by other methods. Also studied was the change in (I) on heat treatments in air, in hydrogen, and in a hydrogen–thiophene mixture. The crystal was found to belong to a hexagonal system. The air-dried sample has about 0.46 mol of water. This water is included as a water molecule, not as hydroxyl. By the dehydration of (I), anhydrous molybdenum trioxide (I′), which has the same crystal structure as (I), is obtained. Another new form of (I′) is the hexagonal trioxide, which is hygroscopic and which easily absorbs water when standing in air. This (I′) is metastable and is irreversibly transformed to rhombic molybdenum trioxide(II) at 420–430 °C. In hydrogen and in a hydrogen-thiophene mixture, reduction and sulfurization occur in addition to transformation, which can be shown schematically as: (Remark: Graphics omitted.). Transformation in hydrogen and in the hydrogen–thiophene mixture proceeds faster than in air. Reduction occurs more quickly in the hydrogen–thiophene mixture than in hydrogen.

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