Molybdenum trioxide


Molybdenum trioxide is chemical compound with the formula MoO3. This compound is produced on the largest scale of any molybdenum compound. It is an intermediate in the production of molybdenum metal. It is also an important industrial catalyst. Molybdenum trioxide occurs as the rare mineral molybdite.

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 molybdenum-oxygen bond to a non-bridging oxygen. Also known is a metastable form of MoO3 with a WO3-like structure.

Preparation and principal reactions

MoO3 is produced industrially by roasting molybdenum disulfide, the chief ore of molybdenum:
The laboratory synthesis of the dihydrate entails acidification of aqueous solutions of sodium molybdate with perchloric acid:
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:
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/Mo 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.
, Questa molybdenum mine, New Mexico

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