Mechanism and Kinetic Study of Reducing MoO3 to MoO2 with CO-15 vol % CO2 Mixed Gases

Converting formaldehyde in methanol with MoO2 under irradiation: A pollution-free strategy for cleaning air

Direct photocatalytic reduction of toxic formaldehyde (HCHO) in value-added chemicals and fuels is promising because that not only abates the environmental pollution, but also solves the energy shortage. Herein, self-supported MoO2 and MoO3 nanoparticles growing on Mo meshes were comparatively applied to the photocatalytic conversion of HCHO. Under UV-visble lights, MoO2 reduces HCHO in methanol (CH3OH) while MoO3 oxidizes HCHO in carbon oxide and water. Their contrary photocatalytic capacities were revealed. Compared with MoO3, the lower work function of MoO2 enables an electron-rich interface, realizing a complete reduction of 30 ppm HCHO to CH3OH in 30 min. Theoretical calculations clarify that a large number of delocalized electrons on MoO2 attracts HCHO molecule and activates its CO bond, facilitating subsequent hydrogenation and reduction of HCHO to CH3OH. As for MoO3, the wider bandgap and higher potential of valence band govern the photocatalytic oxidation of HCHO.

Thermal Stability, Optical and Electrical Properties of Substoichiometric Molybdenum Oxide

Substoichiometric molybdenum oxide ceramics have aroused widespread interest owing to their promising optical and electrical performance. In this work, the thermal stability and decomposition mechanism of Mo₉O₂₆ and Mo₄O₁₁ at 700-1000 °C and 700-1100 °C were investigated, respectively. Based on this information, MoO_x (2 < x < 3) bulk ceramics were prepared by spark plasma sintering (SPS). The results show that Mo₉O₂₆ is stable up to 790 °C in an argon atmosphere. As the temperature rises, it decomposes into Mo₄O₁₁. Mo₄O₁₁ can exist stably at 830 °C, beyond which it will convert to MoO₂. The MoO_x ceramic bulks with four different components (MoO_2.9, MoO_2.8, MoO_2.7 and MoO_2.6) were successfully sintered by SPS, and their relative density was greater than 96.4% as measured by the Archimedes principle. The reflectivity of MoO_x ceramic bulk is low and only 6.3% when the composition is MoO_2.8. The resistivity increases from 10^-3 to 10^-1 Ωcm with the increase in the O/Mo atomic ratio x. In general, the thermal stability information provides a theoretical basis for the processing of MoO_x materials, such as the sintering of the MoO_x target. The optical and electrical properties show that MoO_x is a low-reflective conductive oxide material with great photoelectric application value.

New Solids in As-O-Mo, As(P)-O-Mo(W) and As(P)-O-Nb(W) Systems That Exhibit Nonlinear Optical Properties

Interactions between well-mixed fine powders of As₂O₃, P₂O₅, MoO₃, WO₃ and Nb₂O₅ at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N₂ and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare photosalient effect when crystals physically move in the laser beam. Single crystals' electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids' practical usefulness are discussed.