|Molar mass||143.94 g mol−1|
|Appearance||yellow or light blue solid|
|Density||4.69 g/cm3, solid|
795 °C, 1068 K, 1463 °F
1155 °C, 1428 K, 2111 °F (sublimes)
|Solubility in water||0.1066 g/100 mL (18 °C)
0.490 g/100 mL (28 °C)
2.055 g/100 mL (70 °C)
|Std enthalpy of
|77.78 J K−1 mol−1|
|EU classification||Carc. Cat. 3
|S-phrases||(S2), S22, S36/37|
|LD50||125 mg.kg (rat, oral)|
|Other cations||Chromium trioxide
|Related molybdenum oxides||Molybdenum dioxide
|Related compounds||Molybdic acid
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.
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.
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
- 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
Because of its layered structure and the ease of the Mo(VI)/Mo(V) coupling, MoO3 is of interest in electrochemical devices and displays. 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. However, the issue of keeping the catalyst clean in an environment that would exploit such antimicrobial properties has not been explored.
- Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
- Heynes, J. B. B.; Cruywagen, J. J. (1986). Yellow Molybdenum(VI) Oxide Dihydrate Inorganic Syntheses 24. p. 191. doi:10.1002/9780470132555.ch56. ISBN 0-471-83441-6.
- 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.
- 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 0080379419.
- U.S. Department of Health and Human Services National Toxicology Program
- International Molybdenum Association
- Los Alamos National Laboratory- Molybdenum