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 chemis ...

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. 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 lead ...

compound. The anhydrous oxide is a precursor to molybdenum metal, an important alloying agent. It is also an important industrial

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

. 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 chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

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 achi ...

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 molybdeni ...

, 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 Perchloric acid is a mineral acid with the formula H Cl O4. 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 oxidizer when hot, but aqueo ...

: :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.

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 although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...

by the

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

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. 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 petrol ...

and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

. 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