In Situ X-ray Diffraction Studies on the Reduction of V2 O5 and WO3 by Using Hydrogen.

The reduction of metal oxides with hydrogen is widely used for the production of fine chemicals and metals both on the laboratory and industry scale. In situ methods can help to elucidate reaction pathways and to gain control over such synthesis reactions. In this study, the reduction of WO3 and V2 O5 with hydrogen was investigated by in situ X-ray powder diffraction with regard to intermediates and the influence of heating rates and hydrogen flow rates. Mixtures of V4 O9 , V6 O13 and VO2 in two modifications were identified as intermediates on the way to phase-pure V2 O3 . None of the intermediates occurs in a single phase and therefore cannot be prepared this way. In contrast, the intermediates of the WO3 reduction, H0.23 WO3 and W10 O29 , appear consecutively and can be isolated. For both reactions, the heating and flow rates have little influence on the formation of intermediates.

In Situ X-ray Diffraction Studies on the Production Process of Molybdenum.

During the production of molybdenum, the first reduction step of molybdenum trioxide to molybdenum dioxide is crucial in directing important product properties like particle size and oxygen content. In this study, the influence of heating rate, hydrogen flow, and potassium content on the reduction of MoO3 has been investigated via in situ X-ray powder diffraction. For low heating rates, a molybdenum bronze HxMoO3 could be confirmed as an intermediate, while γ-Mo4O11 can only be observed at high heating rates. Molybdenum formation at temperatures as low as 873 K can be controlled via hydrogen flow. The potassium content of reactants has a direct influence on the amount of Mo4O11 formed during the reaction as well as rates of Mo4O11 and MoO2 formation.

Nickel - p-block metal mixed chalcogenides based on AuCu3-type fragments: iodine-assisted synthesis as a way of obtaining new structures.

Two new mixed nickel-gallium chalcogenides, Ni9.39Ga2S2 and Ni5.80GaTe2, and a new mixed nickel-indium telluride, Ni5.78InTe2, have been synthesized by a high-temperature ampoule route with the addition of iodine, and characterized from single-crystal or powder diffraction data. They belong to the relatively uncommon Ni7-xMQ2/Ni10-xM2Q2 type of structures (M = Ge, Sn, Sb, In), and are built from p-block metal-centered nickel cuboctahedra, alternating along the c axis with defective Cu2Sb-type nickel-chalcogen ones. Both tellurium-containing compounds show a small degree of orthorhombic distortion with respect to the idealized tetragonal structure, only detectable in the powder diffraction data. No phase transition to the tetragonal structure was detected for Ni5.80GaTe2 by the in situ powder diffraction measurements from room temperature to 550 °C. DFT calculations show close relationships of electronic structures of these ternary compounds to their parent intermetallics, Ni3M (M = Ga, In). Metallic conductivity and paramagnetic properties are predicted for all three with the latter confirmed by magnetic measurements. The bonding patterns, investigated via the ELF topological analysis, show multi-centered nickel - p-block metal bonds in the AuCu3-type fragments and pairwise covalent interactions in the nickel-chalcogen fragments. Both Ni7-xMTe2 compounds showed no structural or compositional changes upon high-temperature mid-pressure hydrogenation.