Molybdenum trioxide

Molybdenum trioxide
IUPAC name Molybdenum trioxide
Other names Molybdic anhydride Molybdite Molybdic trioxide
Identifiers
CAS number	1313-27-5 Y ?
Properties
Molecular formula	MoO3
Molar mass	143.94 g mol−1
Appearance	yellow or light blue solid[1]
Density	4.69 g/cm3, solid
Melting point	795 °C
Boiling point	1155 °C
Solubility in water	0.1066 g/100 mL (18 °C) 2.055 g/100 mL (70 °C)
Structure
Crystal structure	orthorhombic
Coordination geometry	see text
Thermochemistry
Std enthalpy of formation ΔfHo298	−745.17 kJ/mol
Standard molar entropy So298	77.78 J K−1 mol−1
Hazards
MSDS	External MSDS
EU Index	042-001-00-9
EU classification	Carc. Cat. 3 Harmful (Xn) Irritant (Xi)
R-phrases	R36/37, R40
S-phrases	(S2), S22, S36/37
Flash point	Non-flammable
Related compounds
Other cations	Chromium trioxide Tungsten trioxide
Related molybdenum oxides	Molybdenum dioxide "Molybdenum blue"
Related compounds	Molybdic acid Sodium molybdate
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

The oxidation state of molybdenum in this compound is +6.

Structure

A section of the chain comprising edge-sharing octahedra. Oxygen atoms above and below the chain link to other chains to build the layer.

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 molydenum-oxygen bond to a non-bridging oxygen.^[2]

Preparation and principal reactions

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

2 MoS₂ + 7 O₂ → 2 MoO₃ + 4 SO₂

The laboratory synthesis entails the acidification of aqueous solutions of sodium molybdate with perchloric acid:^[3]

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) couple, MoO₃ is of interest in electrochemical devices and displays.^[4]

References

1. ^ http://www.mallbaker.com/americas/msds/english/m7829_msds_us_default.pdf
2. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
3. ^ Heynes, J. B. B.; Cruywagen, J. J. "Yellow Molybdenum(VI) Oxide Dihydrate" Inorganic Syntheses, 1986, volume 24, pp. 191. ISBN 0-471-83441-6.
4. ^ 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. Solid State Ionics. 2000, 136-137, 357.

External links

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
• U.S. Department of Health and Human Services National Toxicology Program
• International Molybdenum Association
• Los Alamos National Laboratory- Molybdenum

Molybdite on molybdenite, Questa molybdenum mine, New Mexico. Size: 11.0 x 6.7 x 4.1 cm.