Bulk MoO3 Research Articles

Production of Molybdenum Trioxide Nanosheets by Liquid Exfoliation and Their Application in High-Performance Supercapacitors

Here, we demonstrate a simple method to exfoliate layered molybdenum trioxide (MoO3) crystallites to give multilayer MoO3 nanosheets dispersed in solvents. Exfoliation is achieved by sonicating MoO3 powder in the presence of suitable solvents followed by centrifugation to remove undispersed material. This procedure works well in a range of solvents with Hildebrand solubility parameters close to 21 MPa1/2 and is consistent with the predictions of classical solubility theory. We have fully optimized this process and demonstrated methods to separate the resultant nanosheets by size. Raman spectroscopy suggests the exfoliation process does not damage the MoO3. This is supported by measurements showing that the reaggregated nanosheets display very similar photoluminescence to bulk MoO3. However, the dispersed nanosheets had distinctly different photoluminescence, indicating a decoupling of the monolayers on exfoliation. We have used liquid-exfoliated MoO3 to prepare supercapacitor electrodes that have relative...

MoO2@carbon hollow microspheres with tunable interiors and improved lithium-ion battery anode properties.

MoO2 hollow microspheres with tunable inner space have been synthesized through a hydrothermal process using MoO3 microbelts instead of bulk MoO3 as the precursor. It is found that the reactant morphology has a great impact on the product morphology and the inner space can be tuned by changing the amount of NaOH aqueous solution. An interesting evolutional process from MoO3 microbelts through a rose-like intermediate to MoO2 hollow microspheres has been clearly observed, and thus the possible formation mechanism is revealed. One layer of amorphous carbon has been subsequently coated on the surface of MoO2 hollow microspheres through a simple hydrothermal approach followed by annealing in argon. As the anode material for lithium ion batteries, MoO2@C hollow microspheres manifest excellent lithium-storage properties, such as high capacity (677 mA h g(-1)) and good cycling stability (negligible capacity fading even after 80 cycles). The significantly enhanced performance of MoO2@C hollow microspheres can be attributed to its unique structures, such as nanoscaled primary building blocks, carbon coating, hollow structure, and especially the synergy between the carbon coating and hollow structure.

Partially nitrided molybdenum trioxide with promoted performance as an anode material for lithium-ion batteries

To obtain new anode materials with improved lithium storage properties, molybdenum oxynitride (phase X) was developed from a partial nitridation strategy by heating bulk molybdenum trioxide (MoO3) in a NH3 atmosphere. The elemental mapping shows homogeneous distribution of nitrogen and the nominal composition of the material was well characterized by X-ray photoelectron spectroscopy (XPS) in combination with elemental analysis. The material was evaluated as an anode material for lithium ion batteries for the first time. A reversible capacity of about 980 mA h g−1 was achieved at a current density of 50 mA g−1, showing significantly improved capability retention compared to bulk MoO3, which was due to its increased conductivity. Considering the ease of large-scale fabrication, molybdenum oxynitride should be very promising for lithium ion battery applications. The strategy may also be applied to other metal oxides to improve their performances in lithium ion batteries.

Direct conversion of multilayer molybdenum trioxide to nanorods as multifunctional electrodes in lithium-ion batteries.

In this study we prepared molybdenum trioxide (MoO3) nanorods having average lengths of 0.5-1.5 μm and widths of approximately 100-200 nm through a one-step mechanical break-down process involving favorable fracturing along the crystal direction. We controlled the dimensions of the as-prepared nanorods by applying various imposing times (15-90 min). The nanorods prepared over a reaction time of 90 min were, on average, much shorter and narrower relative to those obtained over 30 min. Evaluations of lithium-ion storage properties revealed that the electrochemical performance of these nanorods was much better than that of bulk materials. As cathodes, the nanorods could deliver a high specific capacity (>315 mA h g(-1)) with losses of less than 2% in the first cycle at a rate of 30 mA g(-1); as anodes, the specific capacity was 800 mA h g(-1) at a rate of 50 mA g(-1). Relative to α-MoO3 microparticles, these nanorods displayed significantly enhanced lithium-ion storage properties with higher reversible capacities and better rate performance, presumably because their much shorter diffusion lengths and higher specific surface areas allowed more-efficient insertion/deinsertion of lithium ions during the charge/discharge process. Accordingly, enhanced physical and/or chemical properties can be obtained through appropriate nanostructuring of materials.

Binder effect on the catalytic activity of MoO3 bulk catalyst reduced by H2 for n-heptane hydroisomerization

Two bulk catalysts containing about 70wt.% of molybdenum trioxide and alumina or silica as binder were prepared by a gel method. They were characterized by X-ray diffraction, Raman spectroscopy, TGA in air and textural properties. The MoO3 bulk catalysts were activated in situ by reduction with hydrogen and tested in the hydroisomerization of n-heptane using a fixed bed continuous flow microreactor coupled to gas chromatograph. The highest catalytic activity for hydroisomerization was obtained with the alumina-based bulk catalyst, although the silica-based bulk catalyst showed lower amounts of cracking products and a higher selectivity to dimethylpentanes. The bulk catalysts resulted more active than MoO3 powder. The results indicate that the acid–base properties of the binder have a desirable effect on the acidity of the molybdenum trioxide powder as hydroisomerization catalyst.

Orthorhombic MoO3 Nanofibers as Cathode Materials for Lithium Batteries

We report the structural and electrochemical properties of MoO3 nanofibers synthesized by hydrothermal reaction from acidified ammonium heptamolybdate tetrahydrate precursor. Structural analysis shows that MoO3 nanofibers 50-80 nm in diameter and a several micrometers in length are grown in the orthorhombic system (Pbnm S.G.). The composition MoO2.9975 was determined by Rietveld refinement and magnetic susceptibility measurements. The electrochemical performance of Li//MoO3 cells with nanofibers deliver a better discharge capacity after 40 cycles than MoO3 bulk.

Enhanced hydrogen generation from methanol aqueous solutions over Pt/MoO3/TiO2 under ultraviolet light

The photocatalytic activity in hydrogen production from methanol reforming can be significantly enhanced by Pt/MoO3/TiO2 photocatalysts. Compared with Pt/P25, the photocatalytic activity of optimized Pt/MoO3/TiO2 shows an evolution rate of 169 μmol/h/g of hydrogen, which is almost two times higher than that of Pt/P25. XRD and Raman spectra show that MoO3 are formed on the surface of TiO2. It is found that with the bulk MoO3 just formed, the catalyst shows the highest activity due to a large amount of heterojunctions and the high crystallinity of MoO3. The HRTEM image showed a close contact between MoO3 and TiO2. It is proposed that the Z-scheme type of heterojunction between MoO3 and TiO2 is responsible for the improved photocatalytic activity. The heterojunction structure of MoO3/TiO2 does not only promote the charge separation, but also separates the reaction sites, where the oxidation (mainly on MoO3) and reduction (on TiO2) reactions occurred.

Effect of hetero atom on dispersion of NiMo phase on M-SBA-15 (M = Zr, Ti, Ti-Zr)

NiMo catalysts were prepared on different hetero atom doped SBA-15 supports for hydrotreatment evaluation. The nature of the hetero atom (Ti, Zr and TiZr) was observed to have a profound impact on the final molybdenum phase formed after calcination of the catalysts. Mo L3 edge XANES analysis of the catalysts along with results from Raman and XRD, show that Zr-SBA-15 support is able to disperse the Molybdenum oxide phase better than the other supports. The formation of bulk phases viz., MoO3 and NiMoO4 is accelerated in pure SBA-15 supports. Evidence of Mo present as tetrahedral MoO4 units was only found in TiZr-SBA-15 support. The presence of tetrahedral Mo species on TiZr-SBA-15 support was attributed to be due to the relative positive charge on the Zr site arising from the electronegative difference between Ti and Zr leading to [MoO4]2− stabilization. Sulfidation studies of the catalysts revealed that formation of active NiMoS phase is maximum in Zr-SBA-15 support and minimum in the SBA-15 supported catalysts. The low sulfidation of Mo in SBA-15 and TiZr-SBA-15 was due to the presence of bulk MoO3 phase. The hydrotreating activities were in confirmation with the characterization studies, with NiMo/Zr-SBA-15 and NiMo/Ti-SBA-15 exhibiting highest HDS and HDN conversions respectively.

Electrochemical properties of nanofibers α-MoO3 as cathode materials for Li batteries

MoO3 nanofibers have been synthesized by hydrothermal reaction from acidified ammonium heptamolybdate tetrahydrate precursor. Characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM), SQUID magnetometry and Raman scattering (RS) spectroscopy. Structural analysis shows that MoO3 nanofibers 50–80 nm in diameter and a several micrometers in length are grown in the orthorhombic system (Pbnm S.G.). The composition MoO2.9975 was determined by Rietveld refinement and magnetic susceptibility measurements. The electrochemical performance of Li//MoO3 cells with nanofibers deliver a better discharge capacity after 40 cycles than MoO3 bulk. Raman spectroscopy studies revealed the structural modulation upon Li intercalation in MoO3 nanofibers. The possible mechanism of intercalation is discussed.

Enhanced nanoscale conduction capability of a MoO2/Graphene composite for high performance anodes in lithium ion batteries

A MoO2/Graphene composite as a high performance anode for Li ion batteries is synthesized by a one pot in-situ low temperature solution phase reduction method. Electron microscopy and Raman spectroscopy results confirm that 2D graphene layers entrap MoO2 nanoparticles homogeneously in the composite. X-ray photoelectron spectroscopy shows the presence of oxygen functionalities on graphene, which allows intimate contact between MoO2 nanoparticles and the graphene. Conductive atomic force microscopy reveals an extraordinarily high nanoscale electronic conductivity for MoO2/Graphene, greater by 8 orders of magnitude in comparison to bulk MoO2. The layered nanostructure and the conductive matrix provide uninhibited conducting pathways for fast charge transfer and transport between the oxide nanoparticles and graphene which are responsible for the high rate capability, a large lithium ion capacity of 770 mAh g−1, and an excellent cycling stability (550 mAh g−1 reversible capacity retained even after 1000 cycles!) at a current density of 540 mA g−1, thereby rendering it to be superior to previously reported values for neat MoO2 or MoO2/Graphene composite. Impedance analyses demonstrate a lowered interfacial resistance for the composite in comparison to neat MoO2. Our results demonstrate the enormous promise that MoO2/Graphene holds for practical Li-ion batteries.

Template-free synthesis of hollow core–shell MoO2 microspheres with high lithium-ion storage capacity

Hollow core–shell MoO2 microspheres were successfully synthesized via a simple one-pot template-free approach for the first time. The crystalline structure of the products was characterized by Powder X-ray diffraction (XRD), the morphology and particle size of the products were analyzed by Transmission Electron Microscope (TEM). The microsphere formation mechanism was discussed, and an Ostwald ripening accompanied by self-assembly process was proposed for the formation of the core–shell and hollow structures. When used as an anode material for lithium ion battery, this unique MoO2 structure could store large amount of Li+, and cycled well. The electrochemical performance of core–shell MoO2 microspheres was much better than that of bulk MoO2.

Transesterification of sunflower oil over MoO 3 supported on alumina

Samples of MoO 3/γ-Al 2O 3 with different MoO 3 loadings (8, 12 and 16 wt%) calcined at different temperatures (800, 950 and 1100 K) have been used in the transesterification of sunflower oil with methanol. Activity was the highest when the samples were calcined at 950 K, the most active catalyst being 16%MoO 3–Al 2O 3. XRD and Raman spectroscopy reveal the presence of many Mo-phases, such as dispersed surface molybdenum specie, bulk MoO 3 and Al 2(MoO 4) 3 in the samples. The influence of various parameters, such as Mo-loading, calcination temperature, reaction temperature and mole ratio of reactants (methanol:oil), on the reaction is presented. The reaction studies have been carried out both in a batch reactor and in a fixed-bed flow reactor. The studies reveal that a sound fixed-bed continuous transesterification process for the production of biodiesel can be designed using MoO 3–Al 2O 3.

Structural Analysis of Silica-Supported Molybdena Based on X-ray Spectroscopy: Quantum Theory and Experiment

Oxygen core excitations in different molecular molybdena–silica models are evaluated using density-functional theory (DFT). These results can be compared with in situ X-ray absorption fine structure (NEXAFS) measurements near the O K-edge of molybdena model catalysts supported on SBA-15 silica, used for exploratory catalytic activity studies. The comparison allows an analysis of structural details of the molybdena species. The silica support is found to contribute to the NEXAFS spectrum in an energy range well above that of the molybdena units, allowing a clear separation between the corresponding contributions. Different types of oxygen species, O(1) in terminal M═O bonds, O(2) in interphase Mo—O—Si bridges and in Mo—O—Mo linkages, as well as O(2) in terminal Mo—O—H groups can be distinguished in the theoretical spectra of the molybdena species with molybdenum in tetrahedral (dioxo species), pentahedral (monooxo species), and octahedral coordination. The experimental NEXAFS spectra exhibit a pronounced double-peak structure in the O 1s to Mo 4d–O 2p excitation range of 529–536 eV. Comparison with the present theoretical data gives clear indications that dioxo molybdena species with tetrahedral MoO4 units can explain the experimental spectrum. This does not fully exclude species with other Mo coordination, like pentahedral. However, the latter are believed to exist in the present samples in much smaller amounts. The experimental NEXAFS spectrum for the supported molybdena species differs substantially from that for MoO3 bulk material with octahedral MoO6 units where the observed asymmetric peak structure is also reproduced by the calculations.

Flame spray synthesis of CoMo/Al 2O 3 hydrotreating catalysts

The first alumina supported and unsupported cobalt molybdenum hydrotreating catalysts have been prepared by one-step flame spray pyrolysis (FSP) by spraying and combusting tris(acetylacetonato)aluminum, cobalt 2-ethylhexanoate and molybdenum 2-ethylhexaoate dissolved in toluene. The oxide particles produced contained varying amounts of transition metals (8, 16, 24 and 32 wt.% Mo with atomic ratio Co/Mo = 1/3 and 16 wt.% Mo with atomic ratios Co/Mo = 2/3 and 1/1) with alumina constituting the balance. In addition, an unsupported reference catalyst (atomic ratio Co/Mo = 1/3) was produced. The particles obtained consisted mostly of γ-Al 2O 3 with some CoAl 2O 4, as evidenced by X-ray diffraction (XRD) and UV–vis spectroscopy. Bulk MoO 3 was not detected by XRD, except at the highest molybdenum content (32 wt.%) and in the unsupported sample, indicating that molybdenum is well dispersed on the surface of the support. The specific surface area as measured by nitrogen adsorption (BET) decreased from 221 to 90 m 2/g when going from the lowest loading supported catalyst (8 wt.%) to the unsupported reference. Transmission electron microscopy (TEM) images showed that at low molybdenum loadings nanoparticle agglomerates with 5–10 nm primary particles were produced. As the molybdenum loading on the alumina was increased from 8 to 32 wt.% and for the unsupported reference the primary particle size increased to up to 20 nm and the morphology became more irregular due to primary particle sintering and aggregation. After activation by sulfidation the activity of the catalysts were measured for the three hydrotreating reactions hydrodesulfurization, hydrodenitrogenation and hydrogenation using a model oil containing dibenzothiophene, indole and naphthalene in n-heptane solution. The best catalyst was the FSP-produced material containing 16 wt.% Mo (atomic ratio Co/Mo = 1/3), which did not contain crystalline MoO 3 and only small amounts of CoAl 2O 4. The hydrotreating activity was approximately 75% of that of commercial cobalt molybdenum catalysts prepared by wet impregnation of pre-shaped alumina extrudates. Since the commercial catalyst is the product of years of development, this shows the potential of the flame spray pyrolysis technique. The Co–Mo–S phase, active for hydrotreating, is formed upon sulfidation of the flame made oxide precursor. TEM images of the spent catalysts showed that as the metal loading was increased from 8 to 32 wt.% Mo the average length of supported MoS 2 entities increased from 3 to 4 nm (for the unsupported catalyst it was 8.5 nm), while the average number of MoS 2 layers per particle increased from 1.1 to 2.5. The increase in MoS 2 particle size resulted in lower activity.

Silica supported amorphous molybdenum catalysts prepared via sol–gel method and its catalytic activity

Silica supported amorphous molybdenum catalysts had been synthesized in alkali, neutral and acidic medium via sol–gel technique. The catalysts were found to be amorphous and free from bulk MoO 3. UV–Vis diffuse reflectance analysis and XPS analysis indicated the co-existence of Mo 5+ and Mo 6+ species when the incorporation was done in acidic medium. The catalytic activity was tested in the liquid phase oxidation of styrene by using hydrogen peroxide as oxidant. The catalyst prepared in acidic medium showed better catalytic activity compared to the catalysts prepared in alkali and neutral medium. The co-existence of Mo 5+ and Mo 6+ species is believed to enhance the catalytic activity. Benzaldehyde was the major product detected. The structure of the catalyst was proposed based on the results obtained from XPS, 29Si MAS NMR, UV–Vis diffuse reflectance and FT-IR spectroscopy.

Single-material multilayer with enhanced photoactivity

Molybdenum trioxide (MoO3) patterned at the nanometer scale is combined with the same material in its bulk form to produce Bragg mirrors with enhanced photoactive properties. MoO3 undergoes coloration with exposure to UV light but a multilayer structure which alternates between nanostructured and bulk MoO3 is 2.5 times more effective. Measurements with various multilayer arrangements suggest the proximity of bulk and nanostructured MoO3 favors the photoreaction with structural water. A possible minor contribution from electronic band shifting is also discussed.

Thermal Spreading As an Alternative for the Wet Impregnation Method: Advantages and Downsides in the Preparation of MoO3/SiO2−Al2O3 Metathesis Catalysts

Silica alumina-supported MoO3 catalysts are classically prepared via impregnation of the support with a molybdenum salt solution, usually ammonium heptamolybdate, and subsequent drying and calcination (three steps). The downsides of such a route for the synthesis of heterogeneous metathesis catalysts are linked to the limited control on the nature of the Mop, stabilized at the surface, to the uneven distribution of the deposit in the pores of the support, and to the build up of inactive species that find their origin in the wet step of the preparation. In opposition, the direct thermal spreading of molybdenum oxide onto the support is a straightforward (one step) method involving no wet stage. It allows the conversion of bulk MoO3 crystals to amorphous molybdate species dispersed at the surface of the silica alumina support. This contribution shows that the catalysts obtained via both methods exhibit similar performances in the self-metathesis of propene to butene and ethene. However, based on XRD, XPS, Raman spectroscopy, ICP-AES, N-2 physisorption, TEM, and MAS-NMR spectroscopy, it is shown that the origin of active and inactive species in the two systems is different. Whereas the activity of wet-made catalysts is limited by the formation of bulky MoO3 crystals and of aluminum molybdate, the performances of dry-made catalysts are limited by the incomplete spreading of MoO3 nanocrystallites.

Origins of Improved Hole‐Injection Efficiency by the Deposition of MoO3 on the Polymeric Semiconductor Poly(dioctylfluorene‐alt‐benzothiadiazole)

AbstractThe electronic structure of the interfaces formed after deposition of MoO3 hole‐injection layers on top of a polymer light‐emitting material, poly(dioctylfluorene‐alt‐benzothiadiazole) (F8BT), is studied by ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy and metastable atom electron spectroscopy. Significant band bending is induced in the F8BT film by MoO3 “acceptors” that spontaneously diffuse into the F8BT “host” probably driven by kinetic energy of the deposited hot MoO3. Further deposition leads to the saturation of the band bending accompanied by the formation of MoO3 overlayers. Simultaneously, a new electronic state in the vicinity of the Fermi level appears on the UPS spectra. Since this peak does not appear in the bulk MoO3 film, it can be assigned as an interface state between the MoO3 overlayer and underlying F8BT film. Both band bending and the interface state should result from charge transfer from F8BT to MoO3, and they appear to be the origin of the hole‐injection enhancement by the insertion of MoO3 layers between the F8BT light‐emitting diodes and top anodes.

Electrochemical hydrogen evolution over MoO 3 nanowires produced by microwave-assisted hydrothermal reaction

Molybdenum trioxide (MoO 3) nanowire with unprecedentedly high aspect ratios (>200) and good crystallinity was prepared via decomposition of (NH 4) 6Mo 7O 24·4H 2O under a microwave-assisted hydrothermal (MH) process. The nanowire was orthorhombic MoO 3 with 50 nm in diameter and 10–12 μm in length. The conventional hydrothermal (CH) reaction required higher temperature and longer reaction times to produce one-dimensional MoO 3, yet its quality was lower. In the electrochemical hydrogen evolution reaction in a H 2SO 4 solution, MoO 3 nanowire from MH process showed much higher electrocatalytic activity than MoO 3 prepared from CH method and commercial bulk MoO 3 particles. The facile vectorial electron transport along the nanowire axis was considered to be responsible for the excellent electrocatalytic activity of the MH–MoO 3 nanowire.

Nitridation of MoO3/HZSM-5 and Fe-MoO3/HZSM-5

Thermal treatment and subsequent ammonolysis of MoO3/H-ZSM-5 is shown to be an effective means for the preparation of zeolite dispersed nitrided molybdenum species. However, it is unlikely that these species reflect the bulk structures formed by analogous treatment of bulk MoO3 precursor. The inclusion of low levels of Fe as a dopant does not produce any apparent effects on the Mo XPS spectra, although the amount of N incorporation is increased, and iron is shown to be reduced to Fe0. FTIR studies evidence the migration of molybdenum oxo species into the zeolite at the temperatures employed.