Molybdenum trioxide describes a family of

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

s with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

MoO₃(H₂O)_n where n = 0, 1, 2. These compounds are produced on the largest scale of any

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

compound. The anhydrous oxide is a precursor to molybdenum metal, an important alloying agent. It is also an important industrial catalyst. It is a yellow solid, although impure samples can appear blue or green. Molybdenum trioxide occurs as the rare mineral

molybdite Molybdite is the naturally occurring mineral form of molybdenum trioxide MoO3. It occurs as yellow to greenish needles and crystallizes in the orthorhombic crystal system. Discovery and occurrence Molybdite was first described in 1854 for and o ...

Structure

In the gas phase, three oxygen atoms are bonded to the central molybdenum atom. In the solid state,

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

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. Also known is a metastable (β) form of MoO₃ with a WO₃-like structure.

Preparation and principal reactions

MoO₃ is produced industrially by roasting

molybdenum disulfide Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is . The compound is classified as a transition metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdenit ...

, the chief ore of molybdenum: : 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: :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 Molybdic acid refers to hydrated forms of molybdenum trioxide and related species. The monohydrate (MoO3·H2O) and the dihydrate (MoO3·2H2O) are well characterized. They are yellow diamagnetic solids. Structure of the solids Solid forms of mo ...

". In base, it dissolves to afford the molybdate anion.

Uses

Molybdenum trioxide is used to manufacture molybdenum metal: :MoO₃ + 3 H₂ → Mo + 3 H₂O Molybdenum trioxide 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. It has been described as "the most commonly used TMO in organic electronics applications ... it is evaporated at relatively low temperature (∼400 °C)." Molybdite-Molybdenite-233200

References

Cited sources

External links

*
U.S. Department of Health and Human Services National Toxicology Program

Los Alamos National Laboratory – Molybdenum
{{oxygen compounds Molybdenum(VI) compounds Transition metal oxides