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.

Contents

Structure

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