Molybdenum trioxide

Molybdenum trioxide
Names
IUPAC name
Molybdenum trioxide
Other names
Molybdic anhydride
Molybdite
Molybdic trioxide
Identifiers
ECHA InfoCard 100.013.823
Properties
MoO3
Molar mass 143.95 g·mol−1
Appearance yellow or light blue solid
Odor odorless
Density 4.69 g/cm3, solid
Melting point 795 °C (1,463 °F; 1,068 K)
Boiling point 1,155 °C (2,111 °F; 1,428 K) sublimes
0.1066 g/100 mL (18 °C)
0.490 g/100 mL (28 °C)
2.055 g/100 mL (70 °C)
+3.0·10−6 cm3/mol
Structure
orthorhombic
see text
Thermochemistry
77.78 J K−1 mol−1
−745.17 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R-phrases (outdated) R36/37, R40
S-phrases (outdated) (S2), S22, S36/37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
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 perchlorateNFPA 704 four-colored diamond
0
3
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
125 mg.kg (rat, oral)
2689 mg/kg (rat, oral)[1]
120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral)[1]
>5840 mg/m3 (rat, 4 hr)[1]
Related compounds
Other cations
 Chromium trioxide
Tungsten trioxide
Molybdenum dioxide
"Molybdenum blue"
Related compounds
 Molybdic acid
Sodium molybdate
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Molybdenum trioxide is chemical compound with the formula MoO3. This compound is produced on the largest scale of any molybdenum compound. It occurs as the rare mineral molybdite. Its chief application is as an oxidation catalyst and as a raw material for the production of molybdenum metal.[2]

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.[3]

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.[3][4]

Preparation and principal reactions

MoO3 is produced industrially by roasting molybdenum disulfide, the chief ore of molybdenum:[2]

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:[5]

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.[6] 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.[7] However, the issue of keeping the catalyst clean in an environment that would exploit such antimicrobial properties has not been explored.

Molybdite on molybdenite, Questa molybdenum mine, New Mexico (size: 11.0×6.7×4.1 cm)

References

  1. 1 2 3 "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 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.
  3. 1 2 Molybdite Mineral Data
  4. ↑ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  5. ↑ Heynes, J. B. B.; Cruywagen, J. J. (1986). "Yellow Molybdenum(VI) Oxide Dihydrate". Inorganic Syntheses. 24: 191–2. doi:10.1002/9780470132555.ch56.
  6. ↑ 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: 357. doi:10.1016/S0167-2738(00)00483-5.
  7. ↑ 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: 47. doi:10.1016/j.msec.2011.09.010.
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
  • U.S. Department of Health and Human Services National Toxicology Program
  • International Molybdenum Association
  • Los Alamos National Laboratory - Molybdenum
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