Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO₃–ZrO₂ catalysts at 400°C. The MoO₃–ZrO₂ solid‐solution catalysts were prepared using the solution combustion method by varying MoO₃ content and temperature. The 15MoO₃–ZrO₂ catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO₂ and dispersed MoO₃ species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO₃–ZrO₂ catalyst showed that the solution combustion method gave well‐dispersed MoO₃ particles on the surface of ZrO₂. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO₃–ZrO₂ catalyst the Mo surface density of 4.2 Mo atoms nm^?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm^?2. The addition of a small amount of MoO₃ to ZrO₂ led to higher tetragonal content of ZrO₂ along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.     

Photoelectrochemical properties of MoO2 thin films

Thin MoO₂ films were electrodeposited on a selenium pre-deposited SnO₂|glass plate. The photoelectrochemical properties of MoO₂ films were investigated in 0.1 M Na₂SO₄ solution by the ultraviolet–visible spectrophotometry, linear sweep voltammetry, and altering current impedance measurement techniques. It was found that under illumination with the incident light of λ?=?366 nm, the photo response of the MoO₂|SnO₂|glass electrode resulted from the MoO₂ layer, while the SnO₂ layer served as a sink for photogenerated charge carriers. The MoO₂ film exhibited n-type conductivity. A schematic band structure diagram of MoO₂ in 0.1 M Na₂SO₄ solution was constructed. The flat band potential (E _fb), the donor concentration (N _D), the photogeneration current efficiency depended on MoO₂ film thickness. The [Fe(CN)₆]^4?/3? redox PEC cell with MoO₂|SnO₂|glass plate as a photoanode was constructed. Power output characteristics such as the open circuit voltage (V _OC), short circuit current (I _SC), the fill factor (FF), and the light-to-electrical conversion efficiency (η) were determined. The maximum light-to-electrical conversion efficiency exhibited by the PEC cell was 0.94 %.     

Electron Beam Induced Transformation of MoO3 to MoO2 and a New Phase MoO

The transformation of MoO₃ induced by electron beam irradiation was studied by electron energy‐loss spectroscopy (EELS) in combination with electron diffraction and high‐resolution transmission electron microscopy (HRTEM) techniques. The routes of structure transformation were dependent on the applied electron current density. In case of low current density, MoO₂ was obtained. In case of high current density, MoO with a rock‐salt structure is suggested to be the final phase. The change in oxidation states of the Mo oxides was deduced from the features in energy‐loss near edge structure (ELNES) of the O K‐edge. Quantitative analysis was successfully employed on Mo M₃‐edge and O K‐edge to obtain the O/Mo ratio of the reduced phases. The mechanisms of different structure transformation behaviors were suggested in the frame of radiolysis enhanced diffusion.     

Study on the formation process of MoO3/Fe2(MoO4)3 by mechanochemical synthesis and their catalytic performance in methanol to formaldehyde

Mechanochemical method has applied to the green preparation of iron-molybdenum catalyst efficiently, and their catalytic performance was evaluated by the oxidation of methanol to formaldehyde. In order to investigate the formation process of iron-molybdenum catalyst based on mechanochemical method, various characterization techniques have been employed. Results indicate that iron-molybdenum catalyst could not be generated during ball milling process without calcining, and calcination is crucial step to regulate the ratio of MoO₃ and Fe₂(MoO₄)₃. For the formation of MoO₃ and Fe₂(MoO₄)₃ phase, 180 °C could be the key turning temperature point. Fe₂(MoO₄)₃ and MoO₃ phases are concurrently emerged when Mo/Fe atomic ratio exceeds 1.5. The aggregation of Fe₂(MoO₄)₃ is severe with the increasing calcination temperature. Fe₂(MoO₄)₃ is stable below 600 °C, while MoO₃ phase could be subliming with the increasing temperature. The catalytic performance of iron-molybdenum catalyst has closely correlation with the phase compositions, which can be controlled by synthesis temperature and Mo/Fe molar ratio. The iron-molybdenum catalyst with Mo/Fe atomic ratio of 2.6 calcined at 500 °C for 4 h showed the best methanol conversion (100%) and formaldehyde yield (92.27%).

     

Hierarchically structured MoO2/dopamine-derived carbon spheres as intercalation electrodes for lithium-ion batteries

A hydrogen peroxide initiated sol-gel process involving molybdenum transformation in the presence of dopamine (Dopa) hydrochloride excess produced the metastable precipitate composed of polydopamine (PDopa) spheres coated with Dopa preintercalated molybdenum oxide, (Dopa)_xMoO_y@PDopa. The hydrothermal treatment (HT) of the (Dopa)_xMoO_y@PDopa precursor resulted in the simultaneous carbonization of Dopa and molybdenum reduction generating MoO₂ nanoplatelets distributed and confined on the surface of the Dopa-derived carbon matrix (HT-MoO₂/C). The consecutive annealing (An) of the HT-MoO₂/C sample at 600 °C under Ar atmosphere led to the formation of MoO₂ with increased Mo oxidation state and improved structural stability (AnHT-MoO₂/C). Annealing had also further facilitated interaction between the molybdenum-derived and Dopa-derived components resulting in the modification of the carbon matrix confirmed by Raman spectroscopy. Morphology of both materials is best described as Dopa-derived carbon spheres decorated with MoO₂ nanoplatelets. These integrated metal oxide and carbon structures were tested as electrodes for lithium-ion batteries in the potential window that corresponds to the intercalation mechanism of charge storage. The AnHT-MoO₂/C electrode showed enhanced electrochemical activity, with an initial specific discharge capacity of 260 mAh/g and capacity retention of 67% after 50 cycles, compared to the HT-MoO₂/C electrode which exhibited an initial specific discharge capacity of 235 mAh g^?1 and capacity retention of 47% after 50 cycles. The rate capability experiments revealed that the capacity of 93 mAh/g and 120 mAh/g was delivered by the HT-MoO₂/C and AnHT-MoO₂/C electrodes, respectively, when the current density was increased to 100 mA/g. The improved specific capacity, electrochemical stability, and rate capability achieved after annealing were attributed to higher crystallinity of MoO₂, increased oxidation state of Mo, and formation of the tighter MoO₂/carbon contact accompanied by the annealing assisted interaction between MoO₂ and Dopa-derived carbon.     

Preparation and properties of rare-earth-molybdenum(V) oxides Ln3MoO7

Phase equilibrium studies in Ln₂O₃MoO₂MoO₃ systems indicate, for a Ln₂O₃:Mo ratio of 3:2, the existence of a new molybdenum (V)-rare-earth oxide Ln₃MoO₇. Ternary oxides have been prepared for Ln ≡ La-Ho and Y. For Ln ≡ La-Eu, Ln₃MoO₇ compounds form at 1473 K under oxygen partial pressures ranging from 10^−7.3 to 10^−11.6 atm. For Ln ≡ Gd-Ho and Y compounds form above 1573 K and at 1473 K the stability range is about 10⁻⁹ to about 10⁻¹⁰ atm. Lattice parameters deduced from X-ray diffraction patterns are reported. For the large Ln cations, lanthanum to europium, all reflections could be indexed in an orthorhombic C-centred cell isotypic to Nd₃NbO₇. For Ln ≡ Gd-Ho and Y, strong f.c.c.-type reflections show that the structure is defect fluorite. Stability ranges in terms of oxygen partial pressure and crystal chemical properties are discussed with respect to the rare-earth elements. Magnetic susceptibility measurements of La₃MoO₇ confirm the oxidation state + 5 for molybdenum.     

The standard molar enthalpy of formation of Ce2(MoO4)3(s) and Sm2(MoO4)3(s) using solution calorimetry

The enthalpies of formations of Ce₂(MoO₄)₃(s) and Sm₂(MoO₄)₃(s) have been measured at 298.15 K using semi adiabatic solution calorimetry. The precipitation reaction between RE(NO₃)₃·6H₂O(s) (R= Ce, Sm) and ammonical solution of Na₂MoO₄(s) was studied. From the enthalpy of precipitation and other required auxiliary data, $ \Updelta_{\text{f}} H_{\text{m}}^{ \circ } \left( { 2 9 8. 1 5 {\text{ K}}} \right) $ Δ f H m ° ( 2 9 8.1 5 K ) of Ce₂(MoO₄)₃(s) and Sm₂(MoO₄)₃(s) have been calculated for the first time as ?4388.7 ± 3.6 and ?4363.4 ± 4.1 kJ mol^?1, respectively. The enthalpy of hydration of anhydrous Ce(NO₃)₃(s) to Ce(NO₃)₃·6H₂O(s) has been calculated. $ \Updelta_{\text{f}} H_{\text{m}}^{ \circ } \left( {{\text{MoO4}}^{ 2- } ,\,{\text{aq}},\, 2 9 8. 1 5 \,{\text{K}}} \right) $ Δ f H m ° ( MoO4 2 ? , aq , 2 9 8.1 5 K ) has also been measured and calculated as ?995.1 kJ mol^?1 from required literature data.     

Li3Al(MoO4)3, a lyonsite molybdate

Trilithium aluminium trimolybdate(VI), Li₃Al(MoO₄)₃, has been grown as single crystals from α‐Al₂O₃ and MoO₃ in an Li₂MoO₄ flux at 998 K. This compound is an example of the well known lyonsite structure type, the general formula of which can be written as A₁₆B₁₂O₄₈. Because this structure can accomodate cationic mixing as well as cationic vacancies, a wide range of chemical compositions can adopt this structure type. This has led to instances in the literature where membership in the lyonsite family has been overlooked when assigning the structure type to novel compounds. In the title compound, there are two octahedral sites with substitutional disorder between Li⁺ and Al³⁺, as well as a trigonal prismatic site fully occupied by Li⁺. The (Li,Al)O₆ octahedra and LiO₆ trigonal prisms are linked to form hexagonal tunnels along the [100] axis. These polyhedra are connected by isolated MoO₄ tetrahedra. Infinite chains of face‐sharing (Li,Al)O₆ octahedra extend through the centers of the tunnels. A mixed Li/Al site, an Li, an Mo, and two O atoms are located on mirror planes.     

New NASICON type oxyanion high capacity anode, Li2Co2(MoO4)3, for lithium-ion batteries: preliminary studies

We describe in this paper the lithium insertion/extraction behavior of a new NASICON type Li₂Co₂(MoO₄)₃ at a low potential and explored the possibility of considering this new oxyanion material as anode for lithium-ion batteries for the first time. Li₂Co₂(MoO₄)₃ was synthesized by a soft-combustion glycine-nitrate low temperature protocol. Test cells were assembled using composite Li₂Co₂(MoO₄)₃ as the negative electrode material and a thin lithium foil as the positive electrode material separated by a microporous polypropylene (Celgard® membrane) soaked in aprotic organic electrolyte (1 M LiPF₆ in EC/DMC). Electrochemical discharge down to 0.001 V from OCV (～3.5 V) revealed that about 35 Li⁺ could ^possibly be inserted into Li₂Co₂(MoO₄)₃ during the first discharge (reduction) corresponding to a specific capacity amounting to 1,500 mAh g^?1. This is roughly fourfold higher compared to that of frequently used graphite electrodes. However, about 24 Li⁺ could be extracted during the first charge. It is interesting to note that the same amount of Li⁺ could be inserted during the second Li⁺ insertion process (second cycle discharge) giving rise to a second discharge capacity of 1,070 mAh g^?1. It was also observed that a major portion of lithium intake occurs below 1.0 V vs Li/Li⁺, which is typical of anodes being used in lithium-ion batteries.     

Tune color of single-phase LiGd(MoO4)2-X(WO4)X: Sm3+, Tb3+ via adjusting the proportion of matrix and energy transfer to create white-light phosphor

A series of LiGd(MO₄)₂: Sm³⁺, Tb³⁺ (M = Mo, W) phosphors was prepared by a conventional solid state reaction method. Powder X-Ray diffraction (XRD) analysis reveals that the compounds are of the same structure type. Their luminescent properties have been studied. The optimal doping concentrations are 8% for Sm³⁺ and 18% for Tb³⁺ in the LiGd(MoO₄)₂ host. Sm³⁺ and Tb³⁺ have different sensitivity to the Mo/W ratio. For LiGd(MoO₄)_2-X(WO₄)_X: Sm³⁺ (X = 0, 0.4, 0.8, 1.2, 1.6, 2.0), the strongest emission intensity is 1.766 times than that of the weakest, while 171 times for LiGd(MoO₄)_2-X(WO₄)_X: Tb³⁺. The experimental results show that Mo/W ratio strong influences on the properties of LiGd(MoO₄)_2-X(WO₄)_X: Tb³⁺. With the increasing of WO₄²⁻ groups concentration, the shape of characteristic excitation peaks of Tb³⁺ is almost the same and the excitation intensity gradually increase. Moreover, the energy transfer from Tb³⁺ to Sm³⁺ has been realized in the co-doped phosphors. The experimental analysis and theoretical calculations reveal that the quadrupole–quadrupole interaction is the dominant mechanism for the Tb³⁺→Sm³⁺ energy transfer. Therefore, luminous intensity can be adjusted by different sensitivities to matrix composition and energy transfer from Tb³⁺→Sm³⁺. By this tuning color method, white-light-emitting phosphor has been prepared. The excitation wavelength is 378 nm, and this indicates that the white-light-emitting phosphor could be pumped by near-UV light.     

Efficient Charge Separation between Bi and Bi2MoO6 for Photoelectrochemical Properties

Herein, porous Bi/Bi₂MoO₆ nanoparticles have been prepared by a facile in‐situ reduction approach. Moreover, the morphology and Bi content of product could be controlled by varying the reaction time. By controlled fabrication, the desired porous Bi₂MoO₆ nanostructure with incorporation of Bi was obtained and exhibited high photoelectric and photocatalytic activity. In particular, the samples yield a photocurrent density of 320 μA cm^?2, which is 3.2 times that of the pure Bi₂MoO₆ nanosheet (100 μA cm^?2) under the same conditions. UV/Vis diffuse reflectance spectroscopy analysis confirmed the surface plasmon resonance in the as‐prepared porous nanoparticles. The improved photoelectric properties could be the synergistic effect of the porous structure with large surface area and effective electron‐hole separations between Bi and Bi₂MoO₆.     

Phase equilibria in the Tl2MoO4-Fe2(MoO4)3-Hf(MoO4)2 system and the crystal structure of ternary molybdate Tl(FeHf0.5)(MoO4)3

The subsolidus region of the ternary salt system Tl₂MoO₄-Fe₂(MoO₄)₃-Hf(MoO₄)₂ was studied by X-ray powder diffraction. New compounds Tl₅FeHf(MoO₄)₆ (5: 1: 2) and Tl(Fe,Hf_0.5)(MoO₄)₃ (1: 1: 1). were found to be formed in this system. Crystals of new ternary molybdate of the composition Tl(FeHf_0.5)(MoO₄)₃ were grown by spontaneous flux crystallization. Its composition and crystal structure were refined based on X-ray diffraction data. The mixed three-dimensional framework of the crystal structure is composed of Mo tetrahedra sharing O vertices with (Fe,Hf)O₆ octahedra. The thallium atoms occupy wide channels in the framework.     

Relationship between V4+ and Mo6+ Contents in V2O5 doped with MoO3

The V⁴⁺ content in V₂O₅ doped with MoO₃ is measured by a spectroscopic method. The influence of the oxygen pressure is also considered. Up to roughly 3.5 at.-% Mo/(Mo+V) the V⁴⁺ fraction is equal to the Mo⁶⁺ fraction for samples sintered in air. Increase of PO₂ gives a decrease in the measured values of the V⁴⁺ fraction for the 5, 10 and 33 at.-% Mo-doped samples.     

Kristallstruktur des Molybdändioxiddichlorid-Phosphoroxidtrichlorid-Addukts MoO2Cl2 · POCl3

Crystal Structure of the Molybdenum Dioxide Dichloride — Phosphorus Oxide Trichloride Adduct MoO₂Cl₂ · POCl₃ The crystal structure of MoO₂Cl₂ · POCl₃ was determined by X-ray methods (R = 0.046; 2497 independent reflexions). MoO₂Cl₂ · POCl₃ crystallizes monoclinic in the space group P2₁/c with Z = 8. It forms nearly linear chains in which the Mo atoms are linked together via weakly bent and asymmetric oxo bridges (Mo? O = 172 and 218 pm). The Mo atoms are surrounded in a distorted octahedral coordination by one O and two Cl atoms (Mo? Cl = 230–232 pm) as terminal ligands and by the POCl₃ molecule and the bridging O atoms as well. The POCl₃ molecule (Mo? O = 233 pm) is located in trans position to the terminal oxo ligand (Mo? O = 166 pm).     

Nano‐MoO3‐modified MCM‐22 for methane dehydroaromatization

The work reported was aimed at a simple method to improve the catalytic activity of Mo/HMCM‐22 in methane aromatization. The catalysts were characterized using X‐ray diffraction, scanning electron microscopy, N₂ adsorption–desorption, NH₃ temperature‐programmed desorption, infrared spectra of pyridine adsorption, X‐ray photoelectron spectroscopy and thermogravimetric analysis. Physicochemical measurements indicated that Mo species with smaller size in HMCM‐22 would sublimate more easily and form Mo species at the atomic/molecular level and then interact well with the internal Brønsted acid sites to form Mo–O–Al active species. Catalytic results confirmed that nano‐MoO₃‐modified HMCM‐22 showed higher methane conversion and aromatics yield (13.1 versus 8.9%) than commercial MoO₃‐modified HMCM‐22 (11.0 versus 7.5%). In addition, nano‐MoO₃‐modified HMCM‐22 showed better durability compared with commercial MoO₃‐modified MCM‐22. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation of Triple‐Shelled Molybdenum–Polydopamine Hollow Spheres and Their Conversion into MoO2/Carbon Composite Hollow Spheres for Lithium‐Ion Batteries

Unique triple‐shelled Mo‐polydopamine (Mo‐PDA) hollow spheres are synthesized through a facile solvothermal process. A sequential self‐templating mechanism for the multi‐shell formation is proposed, and the number of shells can be adjusted by tuning the size of the Mo‐glycerate templates. These triple‐shelled Mo‐PDA hollow spheres can be converted to triple‐shelled MoO₂/carbon composite hollow spheres by thermal treatment. Owing to the unique multi‐shells and hollow interior, the as‐prepared MoO₂/carbon composite hollow spheres exhibit appealing performance as an anode material for lithium‐ion batteries, delivering a high capacity of ca. 580 mAh g^?1 at 0.5 A g^?1 with good rate capability and long cycle life.     

Preparation of MoO3/Pt electrodes by electrodeposition for a direct methanol fuel cell

MoO₃/Pt binary catalysts with various Mo/Pt ratios were prepared by an electrodeposition method for use as the anode in a direct methanol fuel cell. Pt was electrodeposited onto indium tin oxide (ITO) substrate, and then MoO₃ was electrodeposited from an Mo-peroxo electrolyte on the top of Pt with different deposition times. The crystallinity of synthesized films was analyzed by X-ray diffraction (XRD), and the oxidation state of both the platinum and molybdenum were determined by X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM/EDS) was employed to investigate the surface morphology and composition. The catalytic activity and stability for methanol oxidation were measured using cyclic voltammetry and chronoamperometry in a mixture of 0.5 M H₂SO₄ and 0.5 M CH₃OH aqueous solution. Electrocatalytic activity for CO oxidation was also evaluated in a 0.5-M H₂SO₄ solution. The addition of a proper amount of MoO₃ was found to significantly improve both the catalytic activity and stability for methanol oxidation.     

Hydrogen Doping into MoO3 Supports toward Modulated Metal–Support Interactions and Efficient Furfural Hydrogenation on Iridium Nanocatalysts

As promising supports, reducible metal oxides afford strong metal–support interactions to achieve efficient catalysis, which relies on their band states and surface stoichiometry. In this study, in situ and controlled hydrogen doping (H doping) by means of H₂ spillover was employed to engineer the metal–support interactions in hydrogenated MoO_x‐supported Ir (Ir/H?MoO_x) catalysts and thus promote furfural hydrogenation to furfuryl alcohol. By easily varying the reduction temperature, the resulting H doping in a controlled manner tailors low‐valence Mo species (Mo⁵⁺ and Mo⁴⁺) on H?MoO_x supports, thereby promoting charge redistribution on Ir and H?MoO_x interfaces. This further leads to clear differences in H₂ chemisorption on Ir, which illustrates its potential for catalytic hydrogenation. As expected, the optimal Ir/H?MoO_x with controlled H doping afforded high activity (turnover frequency: 4.62 min^?1) and selectivity (>99 %) in furfural hydrogenation under mild conditions (T=30 °C, P =2 MPa), which means it performs among the best of current catalysts.     

On the Reduction of MoO3 to MoO2: A Path to Control the Particle Size and Morphology

During the reduction of molybdenum trioxide (MoO₃) to metallic molybdenum, the first reduction step yielding molybdenum dioxide as an intermediary product is of crucial importance. In this study, we examined the impact of the parameters reduction temperature, water influx, and potassium content on the hydrogen reduction of this first reaction step. Beginning from the same starting material, the chemical vapor transport mechanism was utilized to yield the phase pure MoO₂. Analyses including powder X-ray diffraction, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and high performance optical microscopy were performed on the product phases. Modulations of the specific surface areas of molybdenum dioxide ranging from 2.28 to 0.41 m²/g were possible. Furthermore, a distinct shift from small plate-like grains to cuboid-like forms was achieved.     

β-环糊精诱导的三氧化钼水溶性的增加

报道了由β-环糊精诱导的三氧化钼(MoO₃)水溶性增加及其与β-环糊精浓度的相关性, 认为MoO₃水溶性的增加是由于β-环糊精的加入导致了MoO₃在水中的沉淀-溶解平衡向溶解方向移动. 几个独立的实验证明了由β-环糊精和钼酸根离子(MoO₄^2-)组成的灰蓝色产物的形成. 结果表明: (1) X射线光电子能谱显示, 与MoO₃相比, 灰蓝色产物中钼的3d_5/2和3d_3/2电子轨道的结合能有明显的降低; (2) 在灰蓝色产物中出现了213 nm处的强吸收带(Mo＝O)和775 nm处的宽吸收峰(Mo―O); (3) 由于MoO₄^2-的影响, β-环糊精的质子有很明显的低场漂移. 总之, 我们的工作不仅明确地揭示了β-环糊精和MoO₄^2-之间的分子-离子相互作用, 同时揭示了这种相互作用在改善MoO₃物理性质上的潜在应用价值.