Molybdenum trioxide describes a family of

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

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 betwe ...

MoO₃(H₂O)_n where n = 0, 1, 2. The anhydrous compound is produced on the largest scale of any

molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...

compound since it is the main intermediate produced when molybdenum ores are purified. The anhydrous oxide is a precursor to molybdenum metal, an important alloying agent. It is also an important industrial

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

. It is a yellow solid, although impure samples can appear blue or green. Molybdenum trioxide occurs as the rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

molybdite.

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 Roasting is a cooking method that uses dry heat where hot air covers the food, cooking it evenly on all sides with temperatures of at least from an open flame, oven, or other heat source. Roasting can enhance the flavor through caramelizat ...

the mineral

molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum at ...

(

molybdenum disulfide Molybdenum disulfide (or moly) is an inorganic chemistry, 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 chief ore of molybdenum: : Similar procedures apply to the recovery of molybdenum from spent catalysts. The resulting trioxide can be purified by sublimation. The laboratory synthesis of the dihydrate entails acidification of aqueous solutions of

sodium molybdate Sodium molybdate, Na2MoO4, is useful as a source of molybdenum. This white, crystalline salt is often encountered as the dihydrate, Na2MoO4·2H2O. Preparation Dissolution of MoO3 in sodium hydroxide at 50–70 °C followed by crystallizing t ...

with

perchloric acid Perchloric acid is a mineral acid with the formula H Cl O4. It is an oxoacid of chlorine. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxid ...

: : 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: :MoO₃ + 3 H₂ → Mo + 3 H₂O Molybdenum trioxide is also a component of the co-catalyst used in the industrial production of

acrylonitrile Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid. It has a pungent odor of garlic or onions. Its molecular structure consists of a vinyl group () linked to a nitrile (). It is an im ...

by the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like od ...

and

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

. 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 ransition metal oxidein organic electronics applications ... it is evaporated at relatively low temperature (~400 °C)." It has favourable electronic and chemical properties for use as interfacing layers, p-type

dopants A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optical properties. The amount of dopant is typically very low compared to the material being do ...

and hole transport materials in OLEDs, organic solar cells and perovskite solar cells, especially when forming an

ohmic contact An ohmic contact is a non- rectifying electrical junction: a junction between two conductors that has a linear current–voltage (I–V) curve as with Ohm's law Ohm's law states that the electric current through a Electrical conductor, con ...

to organic semiconductors.

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