Molybdenum trioxide

Molybdenum trioxide is chemical compound with the formula MoO3. This compound is produced on the largest scale of any molybdenum compound. It is an intermediate in the production of molybdenum metal. It is also an important industrial catalyst.[7] Molybdenum trioxide occurs as the rare mineral molybdite.

Molybdenum trioxide
Names
IUPAC name
Molybdenum trioxide
Other names
Molybdic anhydride
Molybdite
Molybdic trioxide
Molybdenum(VI) oxide
Identifiers
ECHA InfoCard 100.013.823
UNII
Properties
MoO3
Molar mass 143.95 g·mol−1
Appearance yellow or light blue solid
Odor odorless
Density 4.70 g/cm3[1]
Melting point 802 °C (1,476 °F; 1,075 K)[1]
Boiling point 1,155 °C (2,111 °F; 1,428 K)(sublimes)[1]
1.066 g/L (18 °C)
4.90 g/L (28 °C)
20.55 g/L (70 °C)
Band gap >3 eV (direct)[2]
+3.0·10−6 cm3/mol[3]
Structure[4]
Orthorhombic, oP16
Pnma, No. 62
a = 1.402 nm, b = 0.37028 nm, c = 0.39663 nm
4
see text
Thermochemistry[5]
75.0 J K−1 mol−1
77.7 J K−1 mol−1
Std enthalpy of
formation (ΔfH⦵298)
 −745.1 kJ/mol
-668.0 kJ/mol
Hazards
Safety data sheet See: data page
Carc. Cat. 3
Harmful (Xn)
Irritant (Xi)
R-phrases (outdated) R36/37, R40
S-phrases (outdated) (S2), S22, S36/37
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity (yellow): no hazard codeSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
0
3
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
125 mg.kg (rat, oral)
2689 mg/kg (rat, oral)[6]
120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral)[6]
>5840 mg/m3 (rat, 4 hr)[6]
Related compounds
Other cations
 Chromium trioxide
Tungsten trioxide
Molybdenum dioxide
"Molybdenum blue"
Related compounds
 Molybdic acid
Sodium molybdate
Supplementary data page
Structure and
properties
 Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
Spectral data
 UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Structure
A section of the chain comprising edge-sharing octahedra. Oxygen atoms in back and front of the chain link to other chains to build the layer.[8]

In the gas phase, three oxygen atoms are double bonded to the central molybdenum atom. In the solid state, anhydrous MoO3 is composed of layers of distorted MoO6 octahedra in an orthorhombic crystal. The octahedra share edges and form chains which are cross-linked by oxygen atoms to form layers. The octahedra have one short molybdenum-oxygen bond to a non-bridging oxygen.[8][9] Also known is a metastable (β) form of MoO3 with a WO3-like structure.[10][2]

Preparation and principal reactions

MoO3 is produced industrially by roasting molybdenum disulfide, the chief ore of molybdenum:[7]

2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2

The laboratory synthesis of the dihydrate entails acidification of aqueous solutions of sodium molybdate with perchloric acid:[11]

Na2MoO4 + H2O + 2 HClO4 → MoO3(H2O)2 + 2 NaClO4

The dihydrate loses water readily to give the monohydrate. Both are bright yellow in color.

Molybdenum trioxide dissolves slightly in water to give "molybdic acid". In base, it dissolves to afford the molybdate anion.

Uses

Molybdenum trioxide is used to manufacture molybdenum metal, which serves as an additive to steel and corrosion-resistant alloys. The relevant conversion entails treatment of MoO3 with hydrogen at elevated temperatures:

MoO3 + 3 H2 → Mo + 3 H2O

It is also a component of the co-catalyst used in the industrial production of acrylonitrile by the oxidation of propene and ammonia.

Because of its layered structure and the ease of the Mo(VI)/Mo(V) coupling, MoO3 is of interest in electrochemical devices and displays.[12] Molybdenum trioxide has also been suggested as a potential anti-microbial agent, e.g., in polymers. In contact with water, it forms H+ ions that can kill bacteria effectively.[13]

Molybdite on molybdenite, Questa molybdenum mine, New Mexico (size: 11.0×6.7×4.1 cm)
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References
  1. Haynes, p. 4.77
  2. Balendhran, Sivacarendran; Walia, Sumeet; Nili, Hussein; Ou, Jian Zhen; Zhuiykov, Serge; Kaner, Richard B.; Sriram, Sharath; Bhaskaran, Madhu; Kalantar-zadeh, Kourosh (2013-08-26). "Two-Dimensional Molybdenum Trioxide and Dichalcogenides". Advanced Functional Materials. 23 (32): 3952–3970. doi:10.1002/adfm.201300125.
  3. Haynes, p. 4.134
  4. Åsbrink, S.; Kihlborg, L. and Malinowski, M. (1988). "High-pressure single-crystal X-ray diffraction studies of MoO3. I. Lattice parameters up to 7.4 GPa". J. Appl. Cryst. 21: 960–962. doi:10.1107/S0021889888008271.CS1 maint: multiple names: authors list (link)
  5. Haynes, p. 5.15
  6. "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  7. Roger F. Sebenik et al. (2005). "Molybdenum and Molybdenum Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_655. ISBN 978-3527306732.CS1 maint: uses authors parameter (link)
  8. "Molybdite Mineral Data". Webmineral.
  9. Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  10. McCarron, E. M. (1986). "β-MoO3: A Metastable Analogue of WO3". J. Chem. Soc., Chem. Commun.: 336–338. doi:10.1039/C39860000336.
  11. Heynes, J. B. B.; Cruywagen, J. J. (1986). "Yellow Molybdenum(VI) Oxide Dihydrate". Inorganic Syntheses. 24: 191–2. doi:10.1002/9780470132555.ch56. ISBN 9780470132555.
  12. Ferreira, F. F.; Souza Cruz, T. G.; Fantini, M. C. A.; Tabacniks, M. H.; de Castro, S. C.; Morais, J.; de Siervo, A.; Landers, R.; Gorenstein, A. (2000). "Lithium insertion and electrochromism in polycrystalline molybdenum oxide films". Solid State Ionics. 136–137 (1–2): 357–363. doi:10.1016/S0167-2738(00)00483-5.
  13. Zollfrank, Cordt; Gutbrod, Kai; Wechsler, Peter; Guggenbichler, Josef Peter (2012). "Antimicrobial activity of transition metal acid MoO3 prevents microbial growth on material surfaces". Materials Science and Engineering: C. 32 (1): 47–54. doi:10.1016/j.msec.2011.09.010. PMID 23177771.

Cited sources
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