Concentration Of Mo5 Research Articles

Defect-original room-temperature hydrogen sensing of MoO3 nanoribbon: Experimental and theoretical studies

Rapid development in the hydrogen energy sector inspires improvement in the sensing properties of low-temperature hydrogen sensors. Both effective experimental researches and simulated calculations are highly beneficial in understanding the sensing mechanism of metal-oxide hydrogen sensors and enhancing their sensing capabilities. In this work, we prepare ultra-long orthorhombic MoO3 nanoribbons using a hydrothermal method. Hydrogen sensors based on single MoO3 are assembled under an optical microscope through a simple process. The concentration of Mo5+ in the nanoribbons can be adjusted by annealing in different atmospheres. The nanoribbon annealed in H2 atmosphere with Mo5+ concentration of ∼25% presents a higher sensor response of 11.23 towards 1000 ppm H2 than those annealed in a vacuum or an O2 atmosphere. Our gas-sensing testing results for different background atmospheres reveal that the oxygen species are closely related to the hydrogen sensing performance. The calculated researches show that pure hydrogen molecules cannot be adsorbed on MoO3 (010) surfaces both with and without defects. Oxygen molecules can capture the electrons from the MoO3 material to form chemisorbed species on the MoO3 (010) surface with terminal oxygen vacancies. The injected H2 gas can react with the pre-adsorbed O2− to form H2O, releasing electrons back to the sensing material. Our theoretical results are in good agreement with those of the experimental investigation.

Molybdenum substitution at the B-site of lanthanum strontium titanate anodes for solid oxide fuel cells

The effects of Mo doping into the B-site of La0.3Sr0.7TiO3-δ perovskite on its ionic conductivity and catalytic activity as an anode material of solid oxide fuel cells have been investigated. The partial substitution of Ti by Mo reduces the bond energy between metal and oxygen ions in the perovskite. The concentration of Mo5+/Mo6+ redox couples increases with the rise of the content of Mo, while the oxygen ionic conductivity decreases simultaneously. The doping of Mo significantly reduces the anodic polarization resistance and improves the performance of the single cell. The cell with La0.3Sr0.7Ti0.97Mo0.03O3-δ anode and La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte exhibits a maximum power density of 135 mW cm−2 at 850 °C with hydrogen as fuel.

Defect structure of nanosized mechanically activated MoO3

Defect structure of mechanically activated MoO3 has been studied with the use of X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance, laser granulometry, and adsorption methods. Two stages of mechanical activation have been distinguished. At mechanical activation doses below 1 kJ/g, the fracture of oxide particles is the main process. At this stage, MoO3 particle sizes decrease from 30 μm to 60 nm and specific surface area linearly increases to 30 m2/g, the sizes of coherent-scattering regions decrease to 18 nm, paramagnetic centers are accumulated, and the Raman spectral bands corresponding to three different types of Mo-O bonds widen and shift. At doses above 1 kJ/g, the main process consists in the friction and aggregation of particles, which is accompanied by some reduction in the specific surface area and an increase in the particle sizes. At the stage of friction, the phase transition from an orthorhombic modification to a monoclinic modification of MoO3 occurs seemingly due to a shift of one layer of the material in plane (100). The shift is accompanied by the accumulation of lattice microstrains in the same plane, formation of “stressed” Mo-O-Mo bridge bonds, and a substantial rise in the concentration of Mo5+ radicals. The maximum total concentration of paramagnetic centers is 1 × 1018 g−1. It may be assumed that the radicals are formed due to the rupture of the most stressed molybdenum-oxygen bridge bonds.

Selective Oxidation of Propane to Acrolein over Ce-Doped Ag–Mo–P–O Catalysts: Influence of Ce Promoter

The selective oxidation of propane to acrolein was performed on Ce-doped Ag0.3Mo0.5P0.3O x catalysts. The maximal acrolein yield of 4.4% with 28.7% acrolein selectivity was obtained on Ce0.1Ag0.3Mo0.5P0.3O y catalyst. The apparent activation energy of Ag0.3Mo0.5P0.3O x catalysts decreased with the addition of Ce. The addition of Ce facilitated the C-H activation of propane and enhanced conversion of intermediate propene to acrolein. The reducibility and the concentration of Mo5+ improved as the Ce content increased and was closely related to acrolein selectivity and propane conversion. The role of Ce in these catalysts was proposed: there was formation of the redox cycle “Ce3+ + Mo6+ ⇔ Ce4+ + Mo5+” in Ce-doped Ag0.3Mo0.5P0.3O x catalysts, leading to the modification of properties and catalytic performance of these catalysts.

Characterization of Catalyst for Coal Liquefaction. Exchange of Hydrogen Attached to Condensed Aromatics with Deuterium in Heavy Water over Catalyst

Abstract The H–D exchange reaction of hydrogen atoms attached to condensed aromatics with deuterium atoms in D2O over catalyst for coal liquefaction was studied by means of D-NMR. MoO3/ZrO2, MoO3/SiO2, Fe2O3–SO42−, SbCl3 and ZnCl2 showed a significant catalytic activity for the exchange reaction. The H–D exchange ability was discussed in terms of the acidic properties and concentration of Mo5+ over supports for coal liquefaction catalysts.

Electron spin resonance study in P2O5-MoO3 and P2O5-MoO3-CaO glasses

ESR spectra of the glass systems P2O5-MoO3 and P2O5-MoO3-CaO are presented. The electron spin resonance results showed a strongly exchange-narrowed interaction with the [Mo5+]/[Mo6+] ratio and line shapes independent of temperature over the range 77 to 300 K. This result supports the concept of temperature-dependent mobility of the carriers and an unchanged paramagnetic site over this temperature range. The more important difference between the spectra of the binary and ternary glasses is that in the former with an increase in MoO3 content the concentration of Mo5+ ions decreases but in ternary glasses it is reversed, i.e. the ion concentration of Mo5+ increases with increase in MoO3 content.

Oxidation of Methanol over SnO2-MoO2- Catalysts

Oxidative dehydrogenation of methanol into formaldehyde was studied over various binary mixtures of metal oxides. Among them SnO2-MoO2- catalyst was the most active and selective. These oxide catalysts were classified into MoO2-containing one and the others on the basis of the conversion-selectivity relationship and CO/CO2 production ratio. The reaction on MoO3containing catalysts probably proceeded in consecutive reactions like CH3OH-ICHOCO.The activity and selectivity over SnO2-MoO2- was little changed in the range of Sn/Mo ratio from 1/9 to 7/3. The fact that HCHO was formed on MoO3 suggests that the activity of SnO2- MoO, is essentially attributed to MoO2-. ESR measurements of SnO2-MoO2- revealed that the concentration of Mo5+ ion is correlated with the catalyst activity.