Molybdenum dioxide

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Molybdenum dioxide
Names
IUPAC name
Molybdenum(IV) oxide
Other names
Molybdenum dioxide
Tugarinovite
Identifiers
ECHA InfoCard
 100.038.746 Edit this at Wikidata
Properties
MoO2
Molar mass 127.94 g/mol
Appearance brownish-violet solid
Density 6.47 g/cm3
Melting point 1,100 °C (2,010 °F; 1,370 K) decomposes
insoluble
Solubility insoluble in alkalies, HCl, HF
slightly soluble in hot H2SO4
+41.0·10−6 cm3/mol
Structure
Distorted rutile (monoclinic)
Octahedral (MoIV); trigonal (O−II)
Hazards
Flash point Non-flammable
Related compounds
Other anions
 Molybdenum disulfide
Other cations
 Chromium(IV) oxide
Tungsten(IV) oxide
"Molybdenum blue"
Molybdenum trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Molybdenum dioxide is the chemical compound with the formula MoO2. It is a violet-colored solid and is a metallic conductor. The mineralogical form of this compound is called tugarinovite, and is only very rarely found. The discovery and early studies of molybdenum dioxide date back to the late 18th and early 19th centuries. One of the notable figures in the history of molybdenum dioxide is the Hungarian chemist Jakob Joseph Winterl (1732-1809). Winterl, who was a professor of chemistry and botany at the University of Budapest, made significant contributions to the understanding of molybdenum compounds. In 1787, he proposed that copper was a compound of nickel, molybdenum, silica, and a volatile substance, showcasing his interest in molybdenum chemistry[1].

Structure

Molybdenum dioxide (MoO2) exists in various crystalline forms, with the most common being the monoclinic (α-MoO2) and hexagonal structures

delocalisation of some of the Mo electrons in a conductance band accounting for the metallic conductivity.[3]

Preparation

One common approach for synthesizing molybdenum dioxide (MoO2) is through the thermal decomposition of molybdenum-containing precursor compounds. For example, ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O) can be used as a precursor and thermally decomposed on an activated carbon support to form crystalline MoO2[4]. The decomposition typically occurs at temperatures in the range of 450-550°C[4]. The thermal behavior and decomposition mechanism of bis(alkylimido)-dichloromolybdenum(VI) adducts with neutral N,N'-chelating ligands has also been studied as precursors for MoO2[5]. It was found that the decomposition follows a general pathway, proceeding first by dissociation of the chelating ligand, then dimerization, intramolecular hydrogen transfer, and ultimately decomposition into molybdenum nitride or carbide species[5]. Understanding the thermal decomposition of Mo precursors is important for designing vapor-phase deposition processes for MoO2 thin films[5].

MoO2 can also be prepared :

2 MoO3 + Mo → 3 MoO2

Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO2 into the volatile species MoO2I2.[7]

Uses

Electronic Applications

Molybdenum dioxide has shown promise in electronic applications due to its high work function and unique properties. In a study on symmetrical junction non-aligned double gate n-channel field effect transistors (NADGNFETs), researchers investigated the effects of metal work function and dielectric constant on device performance[8]. They found that using molybdenum, with a work function of 4.75 eV, as the gate metal significantly affected analog figures of merit such as ON current, ON/OFF current ratio, threshold voltage, and intrinsic gain.

Another study focused on the reliable synthesis of high work-function molybdenum dioxide via atomic layer deposition for next-generation electrode applications[9]. This highlights the potential of MoO2 in advanced electronic devices.

Energy Storage

Molybdenum dioxide has been explored as a component in energy storage systems, particularly in lithium-sulfur (Li-S) batteries. One study prepared one-dimensional molybdenum dioxide–carbon nanofibers (MoO2–CNFs) using an electrospinning technique. When used as a matrix in sulfur/MoO2–CNF cathodes for Li-S batteries, these nanofibers acted as polysulfide reservoirs to alleviate the shuttle effect and improve electrochemical reaction kinetics during charge–discharge processes. The sulfur/MoO2–CNF composites demonstrated high lithium-ion diffusion coefficients, low interfacial resistance, and better electrochemical performance compared to pristine sulfur cathodes.

Another study synthesized nanocomposites of carbon nanotubes (CNTs) with homogeneously anchored MoO2 nanoparticles using a hydrothermal method[10]. When used as an anode in lithium-ion batteries, these MoO2/CNT nanocomposites delivered a higher reversible capacity compared to MoO3 nanobelt/CNT composites and pure MoO2 nanoparticles. The enhanced performance was attributed to the nanocomposite structure, which efficiently enhanced electrical conductivity, lithium-ion diffusion, and maintained electrode integrity during cycling.

Catalysis

Molybdenum dioxide and related compounds have shown catalytic properties in various reactions. One study investigated supported molybdenum carbide and nitride catalysts for carbon dioxide hydrogenation[11]. The catalysts, prepared by wet impregnation followed by thermal treatment, were able to produce CO, methane, methanol, and ethane from CO2. The carbide activity increased with lower carburizing alkane concentration and temperature, and enhanced performance was obtained with pure anatase titania support.

Another study explored the use of liquid or supercritical carbon dioxide (scCO2) as a reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts, including a molybdenum alkylidene complex[12]. The unique properties of scCO2 provided advantages such as convenient workup procedures, catalyst immobilization, and reaction tuning by density control.

Molybdenum dioxide is a constituent of "technical molybdenum trioxide" produced during the industrial processing of

MoS2:[13][14]

2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
MoS2 + 6 MoO3 → 7 MoO2 + 2 SO2
2 MoO2 + O2 → 2 MoO3

MoO2 has been reported as catalysing the

Li-ion batteries.[19][20]

References

  1. ISSN 0021-1753
    .
  2. PMID 28181799
    .
  3. ISBN 0-471-93620-0
  4. ^
    S2CID 222117900
    .
  5. ^
    PMID 36223133
    .
  6. ISBN 0-471-19957-5
  7. ISBN 0-471-30508-1
  8. ISBN 979-8-3503-1908-8
    .
  9. ISSN 2050-7526
    .
  10. ISSN 2046-2069
    .
  11. PMID 32582635
    .
  12. PMID 11552807
    .
  13. ^ Metallurgical furnaces Jorg Grzella, Peter Sturm, Joachim Kruger, Markus A. Reuter, Carina Kogler, Thomas Probst, Ullmans Encyclopedia of Industrial Chemistry
  14. ^ "Thermal Analysis and Kinetics of Oxidation of Molybdenum Sulfides" Y. Shigegaki, S.K. Basu, M.Wakihara and M. Taniguchi, J. Therm. Analysis 34 (1988), 1427-1440
  15. doi:10.1007/BF00914749
  16. doi:10.1007/BF00806906
  17. doi:10.1016/j.fuel.2015.01.003
  18. doi:10.1021/cm020249a
  19. PMID 19775084
    .
  20. OSTI 1370243
    .
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