Mo Precursor Research Articles

A Single-Step Route to Single-Crystal Molybdenum Disulphide (MoS2) Monolayer domains

We report a simple, single-cycle synthetic method for forming highly-crystalline, micron-sized monolayer domains of phase-pure MoS2. This method combines liquid chemistry with discrete, layer-by-layer deposition from a novel Mo precursor. Single-crystalline MoS2 with domain sizes up to 100 μm have been obtained and characterised by optical and electron microscopy as well as Raman and photoluminescence spectroscopy.

Chemical Vapor Deposition Growth of Large-Area Monolayer MoS2 and Fabrication of Relevant Back-Gated Transistor**Supported by the National Natural Science Foundation of China under Grant No 61774064.

A closed two-temperature-zone chemical vapor deposition (CVD) furnace was used to grow monolayer molybdenum disulfide (MoS2) by optimizing the temperature and thus the evaporation volume of the Mo precursor. The experimental results show that the Mo precursor temperature has a large effect on the size and shape transformation of the monolayer MoS2, and at a lower temperature of <760°C, the size of the triangular MoS2 increases with the elevating temperature, while at a higher temperature of >760°C, the shape starts to change from a triangle to a truncated triangle. A large-area triangular monolayer MoS2 with a side length of 145 μm is achieved at 760°C. Further, the as-grown monolayer MoS2 is used to fabricate back-gated transistors by means of electron beam lithography to evaluate the electrical properties of MoS2 thin films. The MoS2 transistors with monolayer MoS2 grown at 760°C exhibit a high on/off current ratio of 106, a mobility of 1.92 cm2/Vs and a subthreshold swing of 194.6 mV/dec, demonstrating the feasible approach of CVD deposition of monolayer MoS2 and the fabrication of transistors on it.

Influence of Ni/Mo ratio on the structure-performance of ordered mesoporous Ni-Mo-O catalysts for oxidative dehydrogenation of propane

Abstract A series of ordered mesoporous Ni-Mo-O catalysts with different ratios of Mo/Ni were prepared by a two-step method, which firstly prepared ordered mesoporous NiO by hard template method and then impregnation with Mo precursor. And their catalytic performance were tested for propane oxidative dehydrogenation. The catalysts were characterization by XRD, N2-adsorption, TEM, XPS, H2-TPR and Raman analyses. It can avoid the dissolution of surface Mo species during etching silica template by a two-step method. And the catalysts with low Mo loading amounts show highly ordered mesoporous structure. A highly proportional β-NiMoO4 phase can exist stably in Ni-Mo-O catalysts at room temperature. And the in-situ Raman results demonstrated the transformation of α-NiMoO4 to β-NiMoO4 with the increasing of temperature. The transformation temperature in this work is relatively low (250 °C) due to the promotion of NiO. The catalyst with Mo/Ni of 0.4 shows the highest activity with the propene yield of 15.6%. The reasons may be from the high β-NiMoO4/α-NiMoO4 ratio, the mesoporous structure and the suitable redox ability.

Polyoxometalates as alternative Mo precursors for methane dehydroaromatization on Mo/ZSM-5 and Mo/MCM-22 catalysts

Catalytic stability and overall performance enhancement for the methane dehydroaromatization process using a combination of hexamolybdate species as Mo precursors and MCM-22 as catalysts support.

Printed Circuit Board-Derived Glass Fiber-Epoxy Resin-Supported Mo-Cu Bimetallic Catalyst for Glucose Synthesis.

A glass fiber-epoxy resin (GFER) framework derived from mixed waste printed circuit boards (MWPCBs) was utilized to prepare a cost-effective, reusable Mo–Cu bimetallic Bronsted–Lewis solid acid catalyst through wet-impregnation under near-infrared radiation (NIRR) activation. The efficacy of the novel Mo–Cu catalyst was assessed in the synthesis of glucose through hydrolysis of jute (Corchorus olitorius) fiber, and the process parameters were optimized (Mo precursor loading: 1.0 wt %, catalyst concentration: 5 wt %, hydrolysis temperature: 80 °C, and hydrolysis time: 10 min) through Taguchi orthogonal design. The GFER support and the prepared catalysts were characterized through thermogravimetric, X-ray diffraction (XRD), Fourier-transform infrared (FTIR), Brunauer–Emmett–Teller (BET)–density functional theory, and TPD analyses. The optimal Mo–Cu catalyst and the GFER support possessed 45.377 and 7.049 m2/g BET area, 0.04408 and 0.02317 cc/g pore volume, 1.9334 and 0.7482 nm modal pore size, and surface acidity of 0.48 and 0.40 mmol NH3/g catalyst, respectively. X-ray photoelectron spectroscopy bands confirmed the coexistence of Mo6+ and Cu2+ species; XRD and FTIR analyses indicated the presence of MoO3 and CuO crystalline phases in all prepared catalysts. The optimal catalyst prepared through NIRR (wavelength 0.75–1.4 μm)-activated hydrothermal treatment resulted in a significantly greater glucose yield (75.84 mol %) than that achieved (53.64 mol %) using a conventionally prepared catalyst. Thus, an energy-efficient application of NIRR (100 W) could significantly improve catalytic properties over conventional hydrothermal treatment (500 W). The present investigation provides an innovative application of MWPCB-derived GFER as a promising cost-effective support for the preparation of highly efficient inexpensive solid catalysts for sustainable synthesis of glucose from low-cost waste jute fiber.

Active phase of dispersed MoS2 catalysts for slurry phase hydrocracking of vacuum residue

Different morphologies of oil-dispersed MoS2 catalysts were obtained by a ligand stabilization method using Mo(CO)6 as a Mo precursor and trioctylphosphine oxide (TOPO) as a coordinating agent to identify the active site of MoS2 in the hydrocracking (HCK) of vacuum residue (VR). Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to obtain structural properties of the dispersed catalyst. It was observed that the MoS2 forms a nanoscaled monolayer from 5 to 10 nm in size. The effect of the oil-dispersed MoS2 catalysts having different morphology on the slurry phase HCK of VR was investigated at 673 K and 9.5 MPa H2. The turnover frequency (TOF) of the dispersed MoS2 catalysts in the VR HCK was found to show a good correlation with the rim-site Mo dispersion of the MoS2 slabs based on the same metal loading of 0.113 mmol at 673 K and 9.5 MPa H2.

Mo2C@NC nanowire bundle for efficient electrocatalytic hydrogen evolution

We demonstrate a novel route for the shape-controlled synthesis of inorganic-organic hybrid nanowire bundle of Mo2C and N-doped carbon (Mo2C@NC) for the electrochemical hydrogen evolution reaction (HER) in acidic and alkaline medium. The synthetic procedure involves the facile complexation of Mo precursor, molybdate, with cationic polymer, poly (diallyldimethylammonium chloride) (PDDA) and the subsequent carburization at 800 °C under optimized condition. The Mo2C@NC nanowire bundle has an average diameter of 75 nm and length of 2.5–4 μm. It has > 67% pyridinic nitrogen and the Mo2C nanowires are coated with N-doped carbon of 2–5 nm thickness. The annealing temperature has large control over the morphology and chemical composition. The electrocatalytic activity of Mo2C@NC is examined in acidic and alkaline solution. The benchmark current density of 10 mA/cm2 in acidic and alkaline pH at overpotential of 135 and 121 mV, respectively. Tafel slope of 61 and 56 mV/dec was obtained in acidic and alkaline pH, respectively. The electrocatalytic HER involves Volmer-Heyrovsky mechanism. The hybrid material has outstanding durability in acidic pH and it retains its initial activity even after 1000 extensive repeated potential cycles. The post-HER analysis reveals that the integrity of Mo2C@NC does not change in acidic pH. The superior performance can be explained by considering the surface morphology of Mo2C and the synergistic effect between the carbide catalyst and N-doped carbon.

Bifunctional MoS2-Silica-Alumina Catalysts for Slurry Phase Phenanthrene-Decalin Hydroconversion

MoS2-amorphous silica-alumina (MoS2-ASA) bifunctional catalysts for slurry-phase hydroconversion of the model reactants phenanthrene and decalin were prepared using three distinct methodologies. The MoS2-ASA catalysts were prepared by (i) a mechanical mixture of MoS2 (prepared separately) and ASA, which were mixed directly in the reactor for the hydroconversion test (MM catalyst); (ii) in situ sulfidation of the molybdenum precursor in the presence of the ASA, both dispersed in the phenanthrene-decalin reaction mixture (IS catalysts); and (iii) impregnation of molybdenum octoate onto ASA, followed by thermal treatment to chemically link the Mo precursor to the ASA surface followed by sulfidation prior to the catalytic test (IMP catalyst). Among the three preparation methods, the MoS2-ASA catalysts prepared in situ (IS) had the highest MoS2 dispersion and degree of sulfidation and yielded the highest hydrogenating activity at the lowest Mo catalyst content (2.9Mo-ASA). Although the MoS2 blocked Bronsted ac...

Carbon nanofiber supported Mo2C catalysts for hydrodeoxygenation of guaiacol: The importance of the carburization process

Molybdenum carbide catalysts supported on carbon nanofibers (β-Mo2C/CNF) were synthetized employing different carburization parameters: five temperatures (550–750 °C) and four heating rates (1–10 °C/min) were tested. The carburization process of the Mo precursor in the catalysts was studied by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, N2 physisorption, inductively coupled plasma optical emission spectrometry and transmission electron microscopy. The formation of the carbide phase was confirmed by the presence of the oxycarbide and carbide phases which were observed on the surface of all catalysts. Higher carburization temperatures resulted in an increase of the carbide phase content and crystal size at the expenses of the oxycarbide phase disappearance. High carburization temperatures and low heating rates were needed in order to obtain well-defined β-Mo2C crystals over the catalysts, which involved a substantial improvement of their catalytic activity in the hydrodeoxygenation of guaiacol.

More active sites exposed few-layer MoSe2 supported on nitrogen-doped carbon as highly efficient and durable electrocatalysts for water splitting

Development of advanced electrocatalysts to drive efficient hydrogen evolution reaction through water splitting is vital in many energy related technologies. Herein the development of nitrogen-doped carbon supported fewer-layer MoSe2 (FL-MoSe2/NC) through calcining the hydrothermal product of the Se and Mo precursors in the presence of ammonium citrate is reported. This FL-MoSe2/NC is highly efficient for the hydrogen evolution reaction (HER) and exhibits a remarkably low onset potential of 15.2 mV, an extremely small overpotential of 74.6 mV (vs. RHE) at 10 mA cm−2, a greatly reduced Tafel slope of 45.2 mV dec−1, and a higher exchange current density of 0.266 mA cm−2. The performance of the FL-MoSe2/NC is much higher than that of most Mo-based HER electrocatalysts reported to date and even comparable to that of other most active non-precious metal based catalysts, suggesting the great potential of using the FL-MoSe2/NC as an efficient catalyst for the HER. The NC is believed to play an important role in the high performance of the FL-MoSe2/NC. It does not only promote a strong interaction between MoSe2 and the NC, but facilitates the formation of MoSe2 with few layers and shorter lattice fringe lengths, which expose more active sites accessible to the HER.

Convenient one step synthesis of molybdenum carbide embedded N-doped carbon nanolayer hybrid architecture using cheap cotton as precursor for efficient hydrogen evolution

The development of low-cost and highly efficient hydrogen evolution reaction (HER) catalysts has driven continuous effort. Here we develop a one-step preparation method of novel two-dimensional coupled hybrid of molybdenum carbide embedded N-doped carbon nanolayer architecture (MoCx-N/CNL) using cheap cotton as carbon and nitrogen precursor and ammonium molybdate as Mo precursor. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive X-ray spectra (EDS), scanning electron microscopy (SEM), element mapping, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the as-prepared nanocomposites. The synergistic effect between dispersive Mo2C particles and N doping in MoCx-N/CNL leads to remarkable HER performance in acidic media. Different amount of Mo were doped in the samples by arranging the ammonium molybdate concentration. Three samples were obtained and MoCx-N/CNL-3 showed better HER electrocatalytic performance than other two samples. Moreover, the as prepared MoCx-N/CNL-3 exhibits excellent stability and durability in acidic media. A new viable route is provided to prepare molybdenum carbide embedded N-doped carbon hybrid architecture with higher HER stability and activity, it is of significance in novel HER catalyst preparation.

Influence of Impregnation Processes on Ruthenium–Molybdenum Carbon Catalysts for Selective Hydrodeoxygenation of Biomass‐Derived Sorbitol into Renewable Alkanes

AbstractSorbitol, as a C6 sugar related compound derived from cellulose, is regarded as a promising biomass‐derived substrate and has characteristically higher oxygen content than in fossil‐based resources. In this work, ruthenium–molybdenum carbon catalysts prepared by different impregnation processes were employed and extensively studied in a trickle‐bed reactor for sorbitol hydrodeoxygenation (HDO). Interestingly, these catalysts afforded remarkably different HDO performance. Ruthenium–molybdenum catalysts prepared by ultrasonic treatment and calcination obtained high HDO performance in sorbitol conversion with 79.8 % carbon yield of C5/C6 alkanes (pentane and hexane), almost twice that of ruthenium–molybdenum catalysts prepared without using a calcination processes. Therefore, a series of characterization studies (N2‐adsorption, XRD, HRTEM, XPS, H2‐TPR, CO‐TPD, NH3‐TPD, Py‐IR spectra, etc.) were performed over relevant catalysts to study the catalytic mechanism. The results suggest that prior calcination offers a better chance for the proximity between Ru and Mo precursors to produce the bimetallic catalytic structure Ru–MoOx, which produces high HDO performance.

Ru-Functionalized Mo2c Nanoparticles in-Situ Grown on Biomass-Derived 3D Porous Carbon Framework for Catalytic Hydrogen Evolution

Developing highly efficient and long-durable electrocatalysts toward the hydrogen evolution reaction (HER) is highly desirable for implementation of the water-splitting to produce high-purity H2 at large scale.[1] Although Pt-group metals so far have been proven to be superior electrocatalysts for HER, the high-cost and scarcity heavily inhibit their widespread application. To date, a series of HER electrocatalysts based on transition metal carbides have been developed. However, in most of these cases, their catalytic activity and durability still need to be improved to compete with Pt-based electrocatalysts.[2, 3] As a cheaper alternative to Pt, Ru possesses similar bond strength with hydrogen, guaranteeing the promise for catalytic hydrogen evolution.[4, 5] In this study, we demonstrate a novel strategy for the preparation of Ru-functionalized Mo2C nanoparticles embedded in popcorn-derived three-dimensional (3D) porous carbon framework. The synthesis mainly involves two steps: (i) the activation of popcorn by KOH and the co-assembly with Ru and Mo precursors. With the help of activation treatment, the popcorn can easily disperse in the solution and absorb Ru and Mo precursor. (ii) freeze-drying followed by in situ annealing treatment. The crystallization of Ru nanoparticles, in-site growth of Mo2C nanoparticles and the carbonization of porous popcorn were simultaneously performed during annealing process. Due to the synergistic effects between Ru and Mo2C nanoparticles, the composite catalyst showed higher HER activity. Figure 1. a) A schematic diagram showing the organization of the Mo2C@Ru. b) HER polarization curves of Mo2C, Ru and Mo2C@Ru with the iR drop correction, acquired at a scan rate of 5 mV s-1 in 0.5 M H2SO4.

Structure and activity of dispersed Co, Ni, or Mo sulfides for slurry phase hydrocracking of vacuum residue

The effects of Co, Ni, or Mo precursors having different oil solubility and oxidation state on the slurry phase hydrocracking (HCK) of vacuum residue (VR) was investigated at 673 K and 9.5 MPa H2. X-ray diffraction and extended X-ray absorption fine structure spectroscopy were used to obtain structural properties of the dispersed catalyst. Under standard operating condition, the metal precursors were found to form nanoscaled dispersed particles of MoS2, Co9S8, and Ni3S2, with the following VR HCK performances in the order MoS2 > Co9S8 ≫ Ni3S2, based on the same metal loading of 0.113 mmol. Among the oil-soluble Mo precursors such as Mo-hexacarbonyl, -octoate, and -naphthenate, it was observed that Mo-octoate having an intermediate oxidation state forms the smallest particles of 5.8 nm in size and shows the best activity in the VR HCK.

Incorporating MoFe alloys into reduced graphene oxide as counter electrode catalysts for dye-sensitized solar cells

In this study, MoFe alloy decorated onto reduced graphene oxide (RGO) nanohybrids is successfully synthesized with various volume ratios of Fe to Mo precursors using a dry plasma reduction method at a low temperature and under atmospheric pressure and is introduced for the first time as an electrocatalyst for counter electrodes (CEs) in dye-sensitized solar cells (DSCs). As observed by HRSEM and TEM analyses, MoFe is successfully immobilized on a 3D network structure of RGO. Well-dispersed MoxFe1−x (0 ≤ x ≤ 1) NPs ranging in size from 2 to 6 nm are stabilized with RGO after co-reduction of the metal precursor ions and graphene oxide. The developed catalysts are then applied as CEs in DSCs. As a result, the Mo0.7Fe0.3/RGO nanohybrid exhibited the highest electrocatalytic activity, corresponding to the lowest charge transfer resistance of 0.11 Ω, among the electrodes tested. The DSC employing Mo0.7Fe0.3/RGO CEs exhibits 5.44% efficiency, which is higher than the 1.26, 4.54 and 4.53% efficiency rates for cells using RGO, Mo0Fe1/RGO and Mo1Fe0/RGO electrodes, respectively, due to the optimization of the catalytic activity and the electron conductivity of the developed materials. Note that the efficiency of the device using a Pt electrode was 5.36% under identical conditions. This study concludes that the CE based on the MoFe/RGO nanohybrid is a prospective substitute for Pt which can provide new opportunities for advancing high-efficiency DSCs. Furthermore, the developed catalysts can be applied to other applications, such as methanol oxidation and oxygen reduction reactions.

Nitroacetylacetone as a Cofuel for the Combustion Synthesis of High-Performance Indium–Gallium–Zinc Oxide Transistors

Thin-film combustion synthesis has been utilized for the fabrication of solution processed high-performance metal-oxide thin-film transistors (MOTFTs) at lower temperatures than conventional sol–gel processes. The fuel-oxidizer ensemble in the MO precursor solution/film plays an important role in achieving high-efficiency and low-residual combustion byproducts. However, unlike conventional bulk combustion, only a very limited number of thin-film fuels have been investigated. Here we report the use of an efficient new cofuel, 3-nitroacetylacetone (NAcAcH), incorporating a −NO2 group, for the combustion synthesis of display-relevant indium–gallium–zinc-oxide (IGZO) thin films. Compared to the traditional acetylacetone (AcAcH) fuel, a higher enthalpy of combustion (988.6 vs 784.4 J/g) and a lower ignition temperature (107.8 vs 166.5 °C) are achieved for NAcAcH-based formulations. The resulting NAcAcH-derived IGZO TFTs exhibit far higher average electron mobilities (5.7 cm2 V–1 s–1) than AcAcH-derived TFTs (2...

Bioinspired Mo2c-Based Catalyst with the Optimized P and S Heteroatom Incorporation for Efficient Hydrogen Production in Alkaline Media

The development of efficient and low-cost catalysts for water splitting is a fundamental challenge for electrochemical hydrogen production. For commercialization of water electrolyzer, highly efficient catalyst for hydrogen evolution reaction (HER) under basic condition is required. Low-cost molybdenum-based catalysts have attracted much attention, but they have not proven to be sufficiently active or stable in alkaline media. Inspired by biomolecular systems, we now present our successful use of polydopamines, a component of adhesive proteins secreted by marine mussels, to synthesize a new, enhanced molybdenum-based catalyst. Moreover, through combinatorial controlling P and S heteroatom elements, further enhanced electrochemical performance was realized. Firstly, to study the effect of P incorporation, we synthesized Mo2C:P using a hydrothermal process. Dopamine (2 mg) was used as a monomer and mixed in tris-(hydroxy-methyl) aminomethane solution (10 mM, pH 8.5). Mo precursors in ammonium heptamolybate (3 mM) and the P precursors in ammonium phosphate (0 to 100 mM) were introduced into the dopamine solution. In order to carbonize the solution, it was dried and then thermally treated in a nitrogen-rich tube furnace at 800 ℃. The electrocatalytic activity of the catalyst was measured using cyclic voltammetry with a rotating disk electrode system in a three-electrode cell at 1M KOH. The 50mM of P sample showed optimal HER catalytic activity, showing the overpotential of 133 mV to attain a current density of 10 mA/cm2. Further improvement could be achieved via S incorporation into the optimized Mo2C:P catalyst. To find optimal concentration of S element, S precursors in sodium sulfide (0 to 50 mM) were introduced into the dopamine solution with Mo and P precursors and the solution was dried and carbonized at 800 ℃. From the current-potential plot, the overpotential was further decreased (113 mV). From XRD, TEM and XPS analysis, we also identified that the incorporation of S and P changed the crystallinity and electronic structure on the surface, possibly resulting in the improved electrochemical performance. In conclusion, we have designed a new bio-mimetic Mo2C:S:P catalyst with enhanced HER properties. The significant catalytic enhancement achieved in this study emphasizes the potential to be explored in strategies applying bioinspired materials as HER catalysts.

Cost-Effective Mo Fe Alloy/Reduced Graphene Oxide Counter Electrodes As a New Avenue for High-Efficiency Dye-Sensitized Solar Cells

MoxFe1-x/reduced graphene oxide (RGO) (0 ≤ x ≤ 1) is successfully synthesized using atmospheric pressure plasma under near room temperature and without using any toxic reagents. HRSEM, TEM, XRD and XPS measurements are conducted to analyze the morphology and chemical composition of the developed materials. Then, the developed materials are applied as Pt-free CEs in DSCs. To obtain efficient CEs, the chemical composition of the MoxFe1-x/RGO is controlled through optimizing the volume ratio of the Mo and Fe precursors during the synthesizing process. The catalytic activity of the developed CEs is carefully evaluated through EIS, CV and Tafel measurements. Finally, the effect of CEs on the efficiency of DSCs is further confirmed by J-V and IPCE performances. As the result, the high conductivity and excellent catalytic activity toward triiodide reduction in CEs of DSCs are obtained for MoxFe1-x/RGO CEs.

Ultra-thin MoO3 film goes wafer-scaled nano-architectonics by atomic layer deposition

From the technical and design points of view, it is quite difficult to maintain the integrity of nano-films during the deposition process to fabricate practical devices based on ultra-thin semiconductor films. Thus, defect-free wafer-scaled development of ultra-thin quasi two-dimensional (2D) oxide semiconductor films represents serious challenges. Plasma-enhanced atomic layer deposition (PE-ALD) made it possible to fabricate ultra-thin MoO3 nano-films (4.6nm) over the wafer-scaled granular Au electrode. The detailed ALD recipe for ultra-thin MoO3 film was established and verified. The C12H30N4Mo and O2 plasma were used as Mo precursor and oxygen source, respectively. The growth of crystalline phases was observed when the ALD temperature of 250°C was employed. Higher ALD temperature resulted in an increase of growth rate over Au substrate (1.21Ǻ/cycle). The precise recipe design enabled the scalable fabrication of environmental sensors based on ultra-thin MoO3 films with precise thickness controllability. Electrochemical sensors based on the fabricated MoO3 nanostructures demonstrated reliable performance to hydrazine (N2H4) detection.

Non-precious molybdenum-based catalyst derived from biomass: CO-free hydrogen production from formic acid at low temperature

CO-free hydrogen was successfully produced from the dehydrogenation of formic acid at a temperature near its boiling point of 110 °C by using a high-performance non-precious metal molybdenum based catalyst synthesized from soybean and earth-abundant molybdenum. The effect of carbonization temperature, raw material ratio on the catalytic activity for formic acid decomposition were investigated in details. The catalyst Soy-Mo (0.1) prepared at a carbonization temperature of 750 °C, the weight ratio of the soybean powder to Mo precursor of 1:0.1 showed the best catalytic activity among those as-synthesized catalysts. Even at a temperature as low as 110 °C, HCOOH conversion reached above 80% with a 100% H2 selectivity and a long-term stability. It indicated that the catalysts derived from those biomass enriched in protein and alkaline metals have excellent performance for catalytic formic acid decomposition. This approach provided a new path for design and development of catalysts with high performance for CO-free hydrogen generation from formic acid in a large-scale industrial process.