Low-temperature synthesis of nano-sized metal molybdate powders

Nanocrystalline metal molybdate [i.e., AMoO₄ where A=Ca(II), Co(II),Cu(II), Ni(II), and Zn(II)] powders have been prepared from the complete evaporation of a polymer-based metal-complex precursor solution. The precursor solution was constituted of the metal ions that were in aqueous solution through complexation with ethylene diamine tetraacetic acid (EDTA) in the presence of diethanolamine (DEA), and a polymeric reagent, which was an aqueous solution mixture of sucrose and polyvinyl alcohol (PVA). Complete dehydration of the precursor solution generated a voluminous mesoporous carbon-rich precursor mass, heat treatment (at temperatures ≤500°C) of which resulted in the respective metal molybdate phase. The average diameter of the particles from transmission electron microscopy and X-ray diffraction studies ranged between 15 and 40 nm.     

新型Mo—Fe（自身载体型复合钼酸铁）催化剂及其生产工艺

阐述了主要应用于甲醇空气氧化法、天然气直接氧化法生产重要有机化工原料甲醛等场合的新型ＭｏＦｅ（自身载体型复合钼酸铁）催化剂的应用要点、特性及其相应的技术经济效果等。主要详述了该新型催化剂的氧化反应催化机理、生产工艺及各步操作方法，进一步的改进措施等。     

New ternary Fe, Co, and Mo mixed oxide electrocatalysts for oxygen evolution

Ternary mixed oxides of Fe, Co, and Mo with composition Fe_xCo_1-xMoO₄ (x = 0.25, 0.50 & 0.75) have been prepared by a co-precipitation method and investigated as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. The study indicates that partial replacement of Co by Fe in the CoMoO₄ matrix increases the specific surface area as well as the apparent electrocatalytic activity of the oxide; the magnitude of increase being the greatest with x = 0.25. The order for the OER with respect to OH⁻ concentration has been observed to be ∼2 on Fe_0.75Co_0.25MoO₄ and ∼1 on Fe_0.25Co_0.75MoO₄ and Fe_0.5Co_0.5MoO₄. The Tafel slopes at low overpotentials were close to 40 mV with each oxide catalyst.     

Synthesis and thermal expansion properties of Y2−xLaxMo3O12 (x=0, 0.5, 2)

Y_2−xLa_xMo₃O₁₂ (x=0, 0.5, 2) ceramics were successfully synthesized by the solid state reaction method. The microstructure, composition and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and dilatometry. Results indicate that the Y_1.5La_0.5Mo₃O₁₂ crystallizes in monoclinic Tb₂Mo₃O₁₂-type structure and it is non-hygroscopic. The Y_1.5La_0.5Mo₃O₁₂ ceramic is denser than the Y₂Mo₃O₁₂ and La₂Mo₃O₁₂ ceramics, and its relative density can reach 94.12% of the theoretical value. Most importantly, it shows almost zero thermal expansion and its thermal coefficient is 0.87×10⁻⁶ K⁻¹ from 178 °C to 600 °C. Y₂Mo₃O₁₂ ceramic shows negative thermal expansion whereas La₂Mo₃O₁₂ ceramic shows positive thermal expansion, their thermal expansion coefficients being−12.06×10⁻⁶ K⁻¹ and 8.88×10⁻⁶×10⁻⁶ K⁻¹, respectively.     

Synthesis and photoluminescent properties of CaMoO4 nanostructures at room temperature

CaMoO₄ nanostructures with different morphologies, such as ellipsoid-like, spindle-like, and sphere-like, were successfully synthesized in a simple cationic surfactant-CTAB-microemulsion system at room temperature. The molar ratio (w) of H₂O to CTAB and the concentration of reactants played important roles in the morphological control of CaMoO₄ nanostructures. A possible mechanism was proposed for the selective formation of the different morphologies. The CaMoO₄ nanostructures exhibited excellent photoluminescence properties with the same new green emission peaks at 495 nm.     

Thermal expansion studies on Th(MoO4)2, Na2Th(MoO4)3 and Na4Th(MoO4)4

Thermal expansion behavior of Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO₄)₂ was synthesized by reacting ThO₂ with 2 mol of MoO₃, at 1073 K in air and Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were prepared by reacting Th(MoO₄)₂ with 1 and 2 mol of Na₂MoO₄, respectively at 873 K in air. The XRD data of Th(MoO₄)₂ was indexed on orthorhombic system where as XRD data of Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were determined from the high temperature data.     

Catalytic properties of Sr2Ni0.75Mg0.25MoO6–δ based composites for application in hydrocarbon-fuelled solid oxide fuel cells

One of the key directions for the development of commercial solid oxide fuel cells fuelled by natural gases consists in the search for efficient fuel electrode materials operated under hydrocarbon-containing atmospheres. Within the present work, we synthesized and characterised novel composites based on a double-perovskite Sr₂Ni_0.75Mg_0.25MoO_6–δ phase and a second phase comprised of SrMoO₄ or NiO. For these composite materials, the reduction behaviour, tolerance to carbon dioxide and catalytic activity towards the partial oxidation of hydrocarbons mixture were comprehensively studied. It is shown that the target properties of the designed composites are affected not only by the type of catalysts but also by the method of their preparation. According to the presented results, the most appropriate materials are composites containing 20 wt% SrMoO₄ or 50 wt% NiO.     

沉淀滴定法测定钼酸钡

采用碳酸钠熔融分解试样，沉淀分离干扰元素，以沉淀滴沔法测定钼酸钡，方法简便快速，结果准确。     

Conductivity and oxygen diffusion in bixbyites and fluorites Ln6−xMoO12−δ (Ln = Er,Tm; x = 0, 0.5)

In the present work erbium and thulium molybdates Ln_5.5MoO_11.25?δ (Ln = Er and Tm) with fluorite and Ln₆MoO_12?δ (Ln = Er and Tm) with bixbyite structure have been studied. The materials have been obtained by mechanical activation method followed by sintering at 1600°С for 3 h. New compounds have been characterized by X-ray diffraction. The total conductivity was investigated using impedance spectroscopy method in dry and wet air. Oxygen diffusivity data was acquired by oxygen isotope exchange with C¹⁸O₂. The combination of different techniques allowed us to determine ionic conductivity components in these compounds. Er and Tm fluorites and bixbyites showed oxygen-ion conductivity in dry air and oxygen-ion and proton conductivity in wet air up to 550–600°С. In wet atmosphere Er and Tm fluorites and bixbyites have total conductivity of about 2?10^?6 S/cm at 500 °C. At higher temperatures they are mixed oxygen-electronic conductors in dry and wet atmosphere. At lower (T < 400 °C) temperatures bixbyites are slightly better ionic conductors compared to fluorites. A high oxygen-ion mobility in all compounds above 200°С has been confirmed by isotope exchange method with С¹⁸O₂: tracer diffusion coefficient values were ~10^?11 – 10^?10 cm²/s at 700 °C. Fluorites were demonstrated to have a higher oxygen mobility compared to bixbyites; the effect is more pronounced for Tm molybdates.     

Intense yellow emission in Dy-doped LiGd(MoO4)2 crystal for visible lasers

The spectroscopic properties of Dy³⁺:LiGd(MoO₄)₂ crystal have been investigated with aim to assess the feasibility of laser operation in the yellow region. On the basis of the analysis of polarized absorption spectra in the framework of the Judd-Ofelt theory, the main spectroscopic characteristics relevant for laser applications have been determined. An intense yellow emission band corresponding to the ⁴F_9/2 → ⁶H_13/2 transition around 575 nm has been observed in the visible region. The emission cross-sections for the ⁴F_9/2 → ⁶H_13/2 transition have been calculated using the Füchtbauer-Ladenburg formula. The fluorescence and radiative lifetimes of the ⁴F_9/2 manifold are equal to 139.0 μs and 199.1 μs, respectively, and the quantum efficiency is 69.8%.