Mixture Of MoO3 Research Articles

Influence of temperature and gas atmosphere on the thermal decomposition of (NH4)6Mo7O24.4H2O

This study investigates the effects of gas atmosphere and synthesis temperature on the thermal decomposition of (NH4)6Mo7O24.4H2O. Samples were synthesized in a CVD furnace at temperatures of 450, 550, and 650 °C, using different gases: H2, O2, and Ar, individually. The resulting samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and optical absorbance. XRD results revealed the formation of MoO3 in all samples produced in an O2 atmosphere. However, in samples synthesized in an inert atmosphere (Ar), a mixture of MoO3 and Mo4O11 phases was detected. The same phase mixture was observed in samples produced at 450 and 550 °C in an H2 atmosphere. However, in samples synthesized in H2 at 650 °C, MoO2 mixed with Mo4O11 was formed. Raman and FTIR spectroscopy confirmed the results obtained by XRD, and these two techniques were also used to compare samples synthesized at 550 °C in different environments. The VSM results indicate a paramagnetic response in the analyzed samples, and there is also an increase in magnetization as the percentage of the Mo4O11 phase increases. Absorbance measurements were also performed and further confirm expected changes in sample composition.

Transformation from MoO3 into MoS2: Experimental study on phase transition and energy band modulation

The transformation of MoO3 into MoS2 is investigated by sulfurizing MoO3 on sapphire at various temperatures. The amorphous MoO3 are crystallized at 500 ℃ and then sulfurized from 500 ℃ to 900 ℃. The phase transition occurs as the temperature increases, from MoO3 to S- doped MoO3 at 500 ℃, mixture of MoO3 and MoS2 at 600 ℃, O- doped MoS2 at 700 ℃, ideal stoichiometric ratio of MoS2 at 800 ℃, and S- deficient MoS2 at 900 ℃, respectively. Correspondingly, the work function is significantly modulated from 4.68 eV for MoO3 to 3.90 eV for MoS2, and the band gap energy decreases from 3.08 eV to 1.00 eV gradually, which are fairly consistent with the theoretical predictions. The contacts between titanium and S- doped MoO3, or the mixture of MoO3 and MoS2, are ohmic- like contacts with specific contact resistivities of 2.68 × 10-3 Ω•cm2 and 3.14 × 10-3 Ω•cm2. While the contacts between Ti and O- doped MoS2, ideal stoichiometric ratio of MoS2, or S- deficient MoS2 are Schottky contacts with barrier heights of 0.22 eV, 0.43 eV and 0.45 eV, respectively. Those results demonstrate that temperature plays pivotal role in determining the phase of sulfurized MoO3 and their properties.

ELECTROREDUCTION OF NICKEL(II) CHLORIDE, COBALT(II) FLUORIDE AND MOLYBDENUM(VI) OXIDE MIXTURES IN A HEAT ACTIVATED BATTERY

The discharge characteristics of the elements of a thermally activated chemical current source (HAB) containing NiCl2–CoF2–MoO3 mixtures as a positive electrode are investigated. It is established that molybdenum oxide stabilizes the discharge plateau and increases the discharge voltage at temperatures above 530°C. The discharge curve has a stepwise character. The number of steps of the discharge curve is determined by the operating conditions of HAB. The low-voltage stage (less than 0.4 V) corresponds to the reduction of lithium molybdates, which are formed by the interaction of molybdenum oxide with the reduction products of transition metal halides. A study of the cathode reduction products by the methods of XRD, STA and SEM was carried out. It is established that during the discharge of the HAB element, the initial components of the cathode mixture are restored to metals that form a dendritic matrix. The DSC curves of the salt fraction formed during electrochemical reactions have a number of thermal effects corresponding to the temperatures of joint melting of a triple mixture of lithium halides LiF–LiCl–LiBr and eutectic dual systems LiF–LiCl, LiCl–Li2O, in which transition metal halides and lithium molybdates are dissolved.

Photochromism of TiO2 Nanoparticles Doped with Molybdenum Ions: Neutral Color Change from Colorless to Black via Gray.

Transition metal oxide nanoparticles have been extensively studied for the development of smart windows which are expected to be a promising technology to save energy in buildings. However, most of them turn blue under UV irradiation. Since the blue coloration affects the color of objects through the windows, the development of materials with a neutral color which hardly disturbs the view is more beneficial. In this work, we prepared a colorless-transparent TiO2 colloidal solution containing Mo6+ ions (Mo-TiO2), which turns black via gray in a nitrogen atmosphere under UV irradiation. An absorption peak was observed at 535 nm, which increased with an increase in the UV irradiation time and reached a constant value (Absmax). The Absmax value increased linearly with an increase in the Mo doping amount. We demonstrated that the photochromic behavior of the Mo-TiO2 nanoparticles is completely different from that of pure MoO3 or the mixture of MoO3 and TiO2. In addition, we performed a kinetic study to elucidate the mechanism and found that the coloration rate at the initial stage decreased with an increase in Mo doping amount. Based on the kinetic analysis, the following results are obtained: a color center is formed at a deeper energy level than the Mo dopant level; the number of the color center depends on the Mo doping amount, and the color center traps the photogenerated electrons more rapidly when it is isolated. The black color was bleached by purging the air in the solution. In particular, the gray state which is observed as a transient color is promising for the development of smart windows to shield the sunlight while allowing a clear and undistorted view.

General synthesis of nanostructured Mo2C electrocatalysts using a carbon template for electrocatalytic applications

Cost-effective and high-active electrocatalysts for the hydrogen evolution reaction (HER) are crucial to sustainable hydrogen generation. Because of the intrinsic Pt-like electronic structure and unique catalytic properties, Mo2C is a promising alternative to Pt-based catalysts. However, synthesis of Mo2C catalysts remains challenging on loss of active sites from structural collapse and sintering at high temperatures. Herein, a facile technique is described to synthesize robust nanostructured Mo2C with a carbon template morphology by salt-assisted chemical vapor deposition (CVD). The highly active metallic vapor precursor generated from the mixture of MoO3 and NaCl facilitates conversion of carbon template into carbide via a novel interface induced propagating synthesis mechanism. The obtained nanostructured Mo2C catalyst has high purity and crystallinity in addition to excellent electrocatalytic activity and stability in both alkaline and acidic media. The results demonstrate a promising synthetic strategy to construct high-quality nanostructured Mo2C and the technique can be extended to other carbide-based electrocatalysts for other energy-related applications.

Molybdenum Oxide Nanoparticle Aggregates Grown by Chemical Vapor Transport.

In this study, the advanced chemical vapor transport (CVT) method in combination with the quenching effect is introduced for creating molybdenum oxide nanoparticle arrays, composed of the hierarchical structure of fine nanoparticles (NPs), which are vertically grown with a homogeneous coverage on the individual carbon fibers of carbon fiber paper (CFP) substrates. The obtained molybdenum oxide NPs hold a metastable high-temperature γ-Mo4O11 phase along with a stable α-MoO3 phase by the quenching effect. Furthermore, such a quenching effect forms thinner and smaller nanoparticle aggregates by suppressing the growth and coalescence of primary particles. The molybdenum oxide nanoparticle aggregates are prepared using two different types of precursors: MoO3 and a 1:1 (mol/mol) mixture of MoO3 and activated carbon. The results characterized using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy show that the relative amount of α-MoO3 to γ-Mo4O11 within the prepared NPs is dependent on the precursor type; a lower amount of α-MoO3 to γ-Mo4O11 is obtained in the NPs prepared using the mixed precursor of MoO3 and carbon. This processing–structure landscape study can serve as the groundwork for the development of high-performance nanomaterials in various electronic and catalytic applications.

Breaking the Scaling Relations in Oxygen Reduction Reaction on MoOy/Pt(CuNi)x Catalyst Toward Enhanced Activity

In recent years, density function theory (DFT) calculations have indicated that the trends in oxygen reduction reaction (ORR) activity of various catalysts can be correlated to the energetics of some key reaction intermediates, which oftentimes leads to a specific trend, namely “volcano plot” where the catalytic activity rises and falls as the absorption free energies of the intermediates change.1 More importantly, researchers found out the absorption free energies of the three species are strongly correlated, which implies the difficulty of optimizing the absorption free energies of the three independently.1,2 This finding suggests that reduction of the energy barrier for one reaction step will presumably lead to an increase for another.2–4 There are several proposed strategies to circumvent the absorption free energy scaling relations, such as N, S-doping,5 introducing additional absorption site,6,7 strain effect,8 etc. Of all the strategies, the introduction of reducible transition oxides has recently shown the great potential in tailing adsorption energies of reaction intermediates on the active sites.In this work, a group of Pt(CuNi)x ternary alloy nanoparticles on carbon support were synthesized using a modified solid-state chemistry method (x = 0.33, 0.5, 0.66, 1, 1.5, 2, 3). It is believed that alloying Pt with transition metals could shift the d-band center of the alloy downwards, which causes lower absorption energy of the intermediate oxygenated species. By changing the composition of Pt(CuNi)x alloy, we could essentially tune the reaction intermediate absorption energy. Interestingly, the ORR catalytic activity test shows as x (i.e., the content of Cu and Ni) increased, the intrinsic area-specific activity (SA) increased, then deceased, exhibiting a “volcano trend” where the Pt(CuNi)0.66 peaked with a SA of 4.15 mA cm-2 Pt. Since the catalytic activity can be correlated with the reaction intermediate absorption energy, the volcano trend can be explained by Pt(CuNi)0.66 alloy having the most suitable intermediate absorption energy compared to alloys with other compositions. However, the scaling relations between oxygenated intermediate species (*O, *OH, and *OOH) limited the further improvement of catalytic activity. Thus, the deposition of molybdenum oxide as an additional active site was proposed to break the scaling relations and improve further beyond the volcano peak. After the typical synthesis of Pt(CuNi)x catalyst, molybdenum hexacarbonyl (Mo(CO)6) was deposited onto the fresh Pt(CuNi)x catalyst and reduced to metallic Mo. The MoOy/Pt(CuNi)x catalyst was obtained by oxidizing Mo to MoOy in the air. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the MoOy consisted of a mixture of MoO3 and MoO2. The electrochemically active area (ECSA) value for MoOy/Pt(CuNi)0.66 decreased from 32.1 to 24.0 m2 g-1 Pt, suggesting a 25% coverage of the metal alloy surface by MoOy. The SA of MoOy/Pt(CuNi)0.66 increased by roughly 14%, from 4.4 to 5.0 mA cm-2 Pt. The SA enhancement was observed for all synthesized MoOy/Pt(CuNi)x catalyst causing the activity volcano plot to shift upwards, which provides strong experimental evidence the activity limit imposed by scaling relations was broken by the deposition of MoOy. The synergistic effect between Pt surface and metal oxides provides several benefits: (i) providing additional active sites for reaction intermediate absorption and reducing the intermediate coverage by enabling spillovers of intermediates between Pt and metal oxide surface.6,7,9 The dual-site cascade oxygen reduction mechanism was reported in detail previously by our group.6 (ii) facilitating O2 absorption and bond breakage by tailoring the electronic structure of adjacent Pt sites.7,10 Therefore, the utilization of reducible transition oxide has shown great potential to overcome the scaling rations to achieve higher ORR activity on Pt-based catalysts.Reference A. Kulkarni, S. Siahrostami, A. Patel, and J. K. Nørskov, Chem. Rev., 118, 2302–2312 (2018).J. K. Nørskov et al., J. Phys. Chem. B, 108, 17886–17892 (2004).Z. W. Seh et al., Science (80-. )., 355, eaad4998 (2017).T. Z. H. Gani and H. J. Kulik, ACS Catal., 8, 975–986 (2018).Y.-Y. Wang, D.-J. Chen, T. C. Allison, and Y. J. Tong, J. Chem. Phys., 150, 41728 (2019).X. Shen et al., J. Am. Chem. Soc., 141, 9463–9467 (2019).W. Gao, Z. Zhang, M. Dou, and F. Wang, ACS Catal., 9, 3278–3288 (2019).A. Khorshidi, J. Violet, J. Hashemi, and A. A. Peterson, Nat. Catal., 1, 263–268 (2018).Z. Awaludin, J. G. S. Moo, T. Okajima, and T. Ohsaka, J. Mater. Chem. A, 1, 14754–14765 (2013).Y. Lu, Y. Jiang, X. Gao, X. Wang, and W. Chen, J. Am. Chem. Soc., 136, 11687–11697 (2014). Figure 1

In situ thermal, optical, and structural investigations on reversible thermochromism in bismuth molybdate

Reversible thermochromic inorganic materials show stable and perceptible color change with changing environmental temperatures. This property makes them excellent materials for fabricating temperature indicators, military camouflage materials, and thermal warning devices. However, the mechanism of thermochromism has not been fully understood. Here, we prepared novel bismuth molybdate materials by calcination of Bi2O3 and MoO3 mixtures. The materials exhibit reversible thermochromism, gradually changing color from milky white at 25 °C to bright yellow at 500 °C. The phase composition of the product is tunable by adjusting the ratio of Bi2O3 and MoO3 in the starting materials, producing either single phase of α-Bi2Mo3O12 or mixed phases of α-Bi2Mo3O12,β-Bi2Mo2O9 and γ-Bi2MoO6. The mechanism of reversible thermochromism was studied by in situ UV/Vis diffuse reflectance spectroscopy (UV/Vis DRS), in situ synchrotron radiation powder X-ray diffraction (SRPXRD), and differential scanning calorimetry (DSC). In situ SRPXRD revealed no phase transition during heating and cooling, which agrees with DSC analysis with no thermal event detected until the melting temperature of α-Bi2Mo3O12 at 661.6 °C. With increasing temperature, in situ SRPXRD also revealed anisotropic expansion of the α-Bi2Mo3O12 lattice parameters, while in situ UV/Vis DRS showed a continuous red shift in the absorption edge and gradual decrease of band gap, suggesting that lattice expansion and shrinking upon heating and cooling is the main reason for the thermochromic behavior in bismuth molybdate materials.

Low-temperature oxidation of Moss—Mo3Si alloys doped by Sc or Y in air and vapor-air mixture

The effect of Sc or Y additives (3% (at.)) on oxidation of Moss—Mo3Si composite in the air and a vapor-air environment (10% H2O) has been studied. It was shown that when heating in the air (500 °C, 100 h) on the surface of samples formed a layer of scale from the mixture of MoO3 + SiO2 and MoO3. Doped alloys were found to oxidize much slower than binary composites. Two process periods with different velocity constants were identified by analysis of kinetic functions. The first period was limited by the oxidation rate of the alloy components and the second one — by sublimation of MoO3 from the surface oxide layer. Sublimation in a humid environment was faster than in the dry air.

Electronic Structure of Molybdenum Oxide Oxidized at Different Pressures

Electronic structure of molybdenum oxides obtained by the oxidation of molybdenum at an oxygen pressure of 1 Torr (thin film) and air (thick film) was studied. It was shown that a thick oxide film is formed from MoO3 oxide, and a thin film from a mixture of MoO3 and MoO2 oxides, which is reflected in the form of valence band spectra. Oxygen on the surface belongs both in molybdenum oxide and in the hydroxyl group, which is associated with dissociative adsorption of water during the oxidation of molybdenum in air for a thick film.

Recycling Molybdenum Oxides from Waste Molybdenum Disilicides: Oxidation Experimental Study and Photocatalytic Properties

To recycle elemental molybdenum from waste molybdenum disilicide (MoSi2) heating elements, the MoSi2 was first disintegrated to MoO3 and SiO2 powders in air at a pest oxidation temperature of 500 °C. X-ray diffraction (XRD) patterns confirmed the completion of the pest oxidation reaction. The mixture of MoO3 and SiO2 powders were heated to 950 °C in a tube furnace to evaporate MoO3, and the XRD patterns of the residue showed that only SiO2 was left in the crucible, confirming that the MoO3 was removed through thermal evaporation. The collected MoO3 crystals had a striped morphology. Photocatalytic performance of MoO3 showed superior activity in comparison with commercial MoO3 and P25 for the degradation of methylene blue under visible light irradiation. The photocatalytic degradation activity of MoO3 synthesized by thermal evaporation at 950 °C was 99.25% in 60 min.

Production of Mo2NiB2 Based Hard Alloys by Self-Propagating High-Temperature Synthesis

Abstract Mo-Ni-B-Al as-cast alloys containing 35.5-58.7 wt% Mo, 23.0-57.6 wt% Ni, 3.3-5.2 wt% B, and 2.2-13.5 wt% Al were synthesized by Self-Propagating High-Temperature Synthesis (SHS) using a mixture of MoO3, NiO, B2O3 and Al powders in order to obtain low-cost Mo2 NiB2 containing hard materials. The first series of experiments were performed using 1.05 times the stoichiometric amount of Al. In the second series of experiments, FactSage thermochemical modeling software was used to minimize Al increasing the Mo2NiB2 formation in the as-cast alloys. The products were characterized by using atomic absorption spectrometry (AAS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness techniques.

Paving the way towards green catalytic materials for green fuels: impact of chemical species on Mo-based catalysts for hydrodeoxygenation.

A series of Mo-based catalysts were synthesized by tuning the sulfidation temperature to produce mixtures of MoO3 and MoS2 as active phases for the hydrodeoxygenation (HDO) of palmitic acid. Differences in the oxidation states of Mo, and the chemical species present in the catalytic materials were determined by spectroscopic techniques. Palmitic acid was used as a fatty-acid model compound to test the performance of these catalysts. The catalytic performance was related to different chemical species formed within the materials. Sulfidation of these otherwise inactive catalysts significantly increased their performance. The catalytic activity remains optimal between the sulfidation temperatures of 100 °C and 200 °C, whereas the most active catalyst was obtained at 200 °C. The catalytic performance decreased significantly at 400 °C due to a higher proportion of sulfides formed in the materials. Furthermore, the relative proportion of MoO3 to MoS2 is essential to form highly active materials to produce O-free hydrocarbons from biomass feedstock. The transition from MoS2 to MoO3 reveals the importance of Mo–S and Mo–O catalytically active species needed for the HDO process and hence for biomass transformation. We conclude that transitioning from MoS2 to MoO3 catalysts is a step in the right direction to produce green fuels.

Facile hydrothermal synthesis of nanorod-structured Mo0.6W0.4O3 catalyst for olefin hydrogenation with high activity

We report a facile hydrothermal synthesis of nanorod-structured molybdenum-tungsten oxides as an efficient catalyst for olefin hydrogenation. The catalytic activity was demonstrated through hydrogenation of cyclohexene used as a model system. The as-prepared material was confirmed as a new phase (Mo0.6W0.4O3) via a series of characterizations, instead of a simple mixture of MoO3 and WO3. The Mo0.6W0.4O3 catalyst displays excellent catalytic activity with 100% conversion of cyclohexene in 3 h, which is much higher than that of pure MoO3 and pure WO3 synthesized with the same method. It was found that hydrogen bronze (HxMo0.6W0.4O3) was formed during the hydrogenation process, and the catalytic performance was positively correlated with the hydrogen content. The obtained nanorod-structured Mo0.6W0.4O3 without loading any noble metal exhibits much higher catalytic activity than a Pd/MoO3 catalyst. The results demonstrate that the nanorod-structured molybdenum-tungsten oxide may be a strong contender for serving as an efficient hydrogenation catalyst alternative to precious metals.

Electroreduction of Chromium(III) Chloride and Molybdenum(VI) Oxide Mixtures in a Thermally Activated Battery

The discharge characteristics of a thermally activated battery element with cathode materials based on CrCl3–MoO3 mixtures are studied. The composition and the morphology of the products of reduction of the cathode materials are determined. A mechanism is proposed for their reduction to metallic chromium and molybdenum through an intermediate stage of formation of the melts of the complex Li3CrCl6 compound and lithium molybdates with lithium chloride.

Synthesis of aluminum oxynitride from MoO3/Al/AlN mixtures by SHS metallurgy

This work investigates the regularities of autowave chemical transformation of MoO3/Al/AlN mixture, gravity separation of its combustion products, and formation of composition and structure of end product (aluminum oxynitride). It is demonstrated that the mixtures of MoO3, Al and AlN are capable of burning in wide ranges of reagent ratios. In the general case, this process is composed of three consecutive stages: stage 1—combustion and chemical transformation of MoO3, Al, and AlN mixture into two-phase melt of end products (autowave synthesis); stage 2—gravity separation of combustion products (metallic and oxide phases), where two layers are generated: upper layer of “light” oxynitride (Al2O3–AlN) and bottom layer of “heavy” intermetallic compound (Mo–Al); stage 3—cooling and generation of phase composition and crystalline structure of metallic and oxide layers. It is established that variation of the aluminum content in the initial mixture at constant content of nitride additive significantly influences the combustion and autowave chemical transformation of the mixture and the phase composition and structure of the end product (aluminum oxynitride). Optimum compositions are determined for obtaining aluminum oxynitrides with high nitrogen content (up to 6–9 wt %) and impurity content (Al7O3N5 and AlN) below 3 wt %. The obtained cast aluminum oxynitride and method of its production are promising for production of high-strength transparent ceramics.

A facile route for large-scale synthesis of molybdenum phosphide nanoparticles with high surface area

GRAPHICAL ABSTRACT

ChemInform Abstract: Single Crystal Growth and Characterization of NaxLn1‐xMoO4, Ln: La, Ce, Pr, Nd, Sm, and Eu (x: 0.397—0.499).

AbstractSingle crystals of the reduced lanthanoid‐containing compounds La0.516Na0.484MoO4, Ce0.512Na0.488MoO4, Pr0.502Na0.498MoO4, Nd0.501Na0.499MoO4, Sm0.509Na0.491MoO4, and Eu0.603Na0.397MoO4 are grown from a NaCl/CsCl eutectic flux by in‐situ reduction using 2:1:0.5 molar mixtures of MoO3, Ln2O3, and Mo, the latter acting as reducing agent (evacuated silica tubes, 825 °C, 24 h; cooling to 450 °C at a rate of 6 °C/h).

ChemInform Abstract: Li3Mo4P5O24: A Two‐Electron Cathode for Lithium‐Ion Batteries with Three‐Dimensional Diffusion Pathways.

AbstractThe new title compound is synthesized by decomposition (350 °C, 6 h) of a gel obtained from an aqueous mixture of MoO3, NH4H2PO4, Li2CO3, and oxalic acid, followed by heating the product twice at 650 and 750 °C for 2 h.

ChemInform Abstract: The Synthesis, Structure and Properties of a New Compound with 1D Linear Chain Arsenomolybdate Anion Building Block.

AbstractThe new compound [Cu(bipy)]2 [H2As2Mo2O14] is hydrothermally synthesized from a mixture of MoO3, CuCl2, Na3AsO4, bipy, HCl, and H2O (autoclave, pH 3.5, 160 °C, 6 d; 58% yield).