Molybdenum trioxide

Molybdenum trioxide

Molybdenum trioxide
IUPAC name
Molybdenum trioxide
Other names
Molybdic anhydride
Molybdic trioxide
 Y  N
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)
see text
77.78 J K−1 mol−1
−745.17 kJ/mol
Safety data sheet See: data page
Carc. Cat. 3
Harmful (Xn)
Irritant (Xi)
R-phrases R36/37, R40
S-phrases (S2), S22, S36/37
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
125 (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
Related molybdenum oxides
Molybdenum dioxide
"Molybdenum blue"
Related compounds
Molybdic acid
Sodium molybdate
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N  (: Y/N?)

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 1
  • Preparation and principal reactions 2
  • Uses 3
  • References 4
  • External links 5


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.


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.[4] 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.[5] 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)


  1. ^ a b c "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life and Health.  
  2. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  3. ^ Heynes, J. B. B.; Cruywagen, J. J. (1986). Yellow Molybdenum(VI) Oxide Dihydrate Inorganic Syntheses 24. p. 191.  
  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. (2000). "Lithium insertion and electrochromism in polycrystalline molybdenum oxide films". Solid State Ionics. 136–137: 357.  
  5. ^ 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.  

External links

  • U.S. Department of Health and Human Services National Toxicology Program
  • International Molybdenum Association
  • Los Alamos National Laboratory - Molybdenum