Molybdenum trioxide

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Molybdenum trioxide
Molybdan(VI)-oxid Kristallstruktur.png
Molybdenum trioxide powder.jpg
IUPAC name
Molybdenum trioxide
Other names
Molybdic anhydride
Molybdic trioxide
Molybdenum(VI) oxide
ECHA InfoCard 100.013.823
PubChem CID
Molar mass 143.95 g·mol−1
Appearanceyellow or light blue solid
Odor odorless
Density 4.70 g/cm3 [1]
Melting point 802 °C (1,476 °F; 1,075 K) [1]
Boiling point 1,155 °C (2,111 °F; 1,428 K)(sublimes) [1]
1.066 g/L (18 °C)
4.90 g/L (28 °C)
20.55 g/L (70 °C)
+3.0·10−6 cm3/mol [2]
Structure [3]
Orthorhombic, oP16
Pnma, No. 62
a = 1.402 nm, b = 0.37028 nm, c = 0.39663 nm
see text
Thermochemistry [4]
75.0 JK−1mol−1
77.7 JK−1mol−1
−745.1 kJ/mol
-668.0 kJ/mol
Safety data sheet See: data page
Carc. Cat. 3
Harmful (Xn)
Irritant (Xi)
R-phrases (outdated) R36/37, R40
S-phrases (outdated) (S2), S22, S36/37
NFPA 704
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity (yellow): no hazard codeSpecial hazard OX: Oxidizer. E.g. potassium perchlorateMolybdenum trioxide
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
125 (rat, oral)[ citation needed ]
2689 mg/kg (rat, oral) [5]
120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral) [5]
>5840 mg/m3 (rat, 4 hr) [5]
Related compounds
Other cations
Chromium trioxide
Tungsten trioxide
Molybdenum dioxide
"Molybdenum blue"
Related compounds
Molybdic acid
Sodium molybdate
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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. [6] Molybdenum trioxide occurs as the rare mineral molybdite.

Chemical compound Substance composed of multiple elements

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. Two atoms of the same element bonded in a molecule do not form a chemical compound, since this would require two different elements.

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

Molybdenum Chemical element with atomic number 42

Molybdenum is a chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.



A section of the chain comprising edge-sharing octahedra. Oxygen atoms in back and front of the chain link to other chains to build the layer. MoO3 chains.png
A section of the chain comprising edge-sharing octahedra. Oxygen atoms in back and front of the chain link to other chains to build the layer.

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. [7] [8] Also known is a metastable (β) form of MoO3 with a WO3-like structure. [9]

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 achieve perfect dryness; anhydrous compounds gradually absorb water from the atmosphere so they must be stored carefully.

Tungsten trioxide chemical compound

Tungsten(VI) oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal. Tungsten trioxide is a strong oxidative agent, it reacts rare-earth elements, iron, copper, aluminium, manganese, zinc, chromium, molybdenum, carbon, hydrogen and silver to make the pure tungsten metal, and gold and platinum to make the tungsten dioxide.

Preparation and principal reactions

MoO3 is produced industrially by roasting molybdenum disulfide, the chief ore of molybdenum: [6]

Molybdenum disulfide chemical compound

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS

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: [10]

Sodium molybdate chemical compound

Sodium molybdate, Na2MoO4, is useful as a source of molybdenum. It is often found as the dihydrate, Na2MoO4·2H2O.

Perchloric acid chemical compound

Perchloric acid is a mineral acid with the formula HClO4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid and nitric acid. It is a powerful oxidizer when hot, but aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate, an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures.

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.

Molybdic acid chemical compound

Molybdic acid refers to hydrated forms of molybdenum trioxide and related species. The monohydrate is MoO3·H2O and the dihydrate (MoO3·2H2O) are well characterized. They are yellow diamagnetic solids.


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

It is also a component of the co-catalyst used in the industrial production of acrylonitrile by the oxidation of propene and ammonia.

Acrylonitrile is an organic compound with the formula CH2CHCN. It is a colorless volatile liquid, although commercial samples can be yellow due to impurities. In terms of its molecular structure, it consists of a vinyl group linked to a nitrile. It is an important monomer for the manufacture of useful plastics such as polyacrylonitrile. It is reactive and toxic at low doses. Acrylonitrile was first synthesized by the French chemist Charles Moureu (1863–1929) in 1893.

Propene, also known as propylene or methyl ethylene, is an unsaturated organic compound having 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 odor

Ammonia Chemical compound of nitrogen and hydrogen

Ammonia is a compound of nitrogen and hydrogen with the formula NH3. The simplest pnictogen hydride, ammonia is a colourless gas with a characteristic pungent smell. It is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products. It is mainly collected by downward displacement of both air and water. Ammonia is named for the Ammonians, worshipers of the Egyptian god Amun, who used ammonium chloride in their rituals.

Because of its layered structure and the ease of the Mo(VI)/Mo(V) coupling, MoO3 is of interest in electrochemical devices and displays. [11] 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. [12]

Molybdite on molybdenite, Questa molybdenum mine, New Mexico (size: 11.0x6.7x4.1 cm) Molybdite-Molybdenite-233200.jpg
Molybdite on molybdenite, Questa molybdenum mine, New Mexico (size: 11.0×6.7×4.1 cm)

Related Research Articles

An oxyanion, or oxoanion, is an ion with the generic formula A
. Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determined by the octet rule. The corresponding oxyacid of an oxyanion is the compound H
. The structures of condensed oxyanions can be rationalized in terms of AOn polyhedral units with sharing of corners or edges between polyhedra. The phosphate and polyphosphate esters adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) are important in biology.

Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3, with a relatively narrow liquid range. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain.

Wulfenite molybdate mineral

Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".

Chromium trioxide chemical compound

Chromium trioxide is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating. Chromium trioxide is a powerful oxidiser and a suspected carcinogen.

Phosphorus pentoxide Chemical compound

Phosphorus pentoxide is a chemical compound with molecular formula P4O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent.

Selenic acid is the inorganic compound with the formula H
. It is an oxoacid of selenium, and its structure is more accurately described as (HO)
. It is a colorless compound. Although it has few uses, its derivative sodium selenate is used in the production of glass and animal feeds.

Bismuth(III) oxide chemical compound

Bismuth(III) oxide is perhaps the most industrially important compound of bismuth. It is also a common starting point for bismuth chemistry. It is found naturally as the mineral bismite (monoclinic) and sphaerobismoite, but it is usually obtained as a by-product of the smelting of copper and lead ores. Bismuth trioxide is commonly used to produce the "Dragon's eggs" effect in fireworks, as a replacement of red lead.

Heteropoly acid class of acid made up of a particular combination of hydrogen and oxygen with certain metals and non-metals. This type of acid is a common re-usable acid catalyst in chemical reactions

A heteropoly acid is a class of acid made up of a particular combination of hydrogen and oxygen with certain metals and non-metals. This type of acid is a common re-usable acid catalyst in chemical reactions.

Metal aromaticity is the concept of aromaticity found in many organic compounds is extended to metals. The first experimental evidence for the existence of aromaticity in metals was found in aluminium cluster compounds of the type MAl4 where M stands for lithium, sodium or copper. These anions can be generated in a helium gas by laser vaporization of an aluminium / lithium carbonate composite or a copper or sodium / aluminium alloy, separated and selected by mass spectrometry and analyzed by photoelectron spectroscopy. The evidence for aromaticity in these compounds is based on several considerations. Computational chemistry shows that these aluminium clusters consist of a tetranuclear Al42− plane and a counterion at the apex of a square pyramid. The Al42− unit is perfectly planar and is not perturbed the presence of the counterion or even the presence of two counterions in the neutral compound M2Al4. In addition its HOMO is calculated to be a doubly occupied delocalized pi system making it obey Hückel's rule. Finally a match exists between the calculated values and the experimental photoelectron values for the energy required to remove the first 4 valence electrons.

Antimony pentoxide chemical compound

Antimony pentoxide (molecular formula: Sb2O5) is a chemical compound of antimony and oxygen. It always occurs in hydrated form, Sb2O5·nH2O. It contains antimony in the +5 oxidation state.

Keggin structure

Keggin structure is the best known structural form for heteropoly acids. It is the structural form of α-Keggin anions, which have a general formula of [XM12O40]n, where X is the heteroatom (most commonly are P5+, Si4+, or B3+), M is the addenda atom (most common are molybdenum and tungsten), and O represents oxygen. The structure self-assembles in acidic aqueous solution and is the most stable structure of polyoxometalate catalysts.

Molybdenum dioxide is the chemical compound with the formula MoO2. It is a violet-colored solid and is a metallic conductor. It crystallizes in a monoclinic cell, and has a distorted rutile, (TiO2) crystal structure. In TiO2 the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO2 the octahedra are distorted, the Mo atoms are off-centre, leading to alternating short and long Mo – Mo distances and Mo-Mo bonding. The short Mo – Mo distance is 251 pm which is less than the Mo – Mo distance in the metal, 272.5 pm. The bond length is shorter than would be expected for a single bond. The bonding is complex and involves a delocalisation of some of the Mo electrons in a conductance band accounting for the metallic conductivity.
MoO2 can be prepared :

Molybdenum blue pigment

Molybdenum blue is a term applied to:

A transition metal oxo complex is a coordination complex containing an oxo ligand. Formally O2-, an oxo ligand can be bound to one or more metal centers, i.e. it can exist as a terminal or (most commonly) as bridging ligands (Fig. 1). Oxo ligands stabilize high oxidation states of a metal.

Molybdate anion, oxysalt

In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state.The larger oxoanions are members of group of compounds termed polyoxometalates, and because they contain only one type of metal atom are often called isopolymetalates. The discrete molybdenum oxoanions range in size from the simplest MoO2−
, found in potassium molybdate up to extremely large structures found in isopoly-molybdenum blues that contain for example 154 Mo atoms. The behaviour of molybdenum is different from the other elements in group 6. Chromium only forms the chromates, CrO2−
, Cr
, Cr
and Cr
ions which are all based on tetrahedral chromium. Tungsten is similar to molybdenum and forms many tungstates containing 6 coordinate tungsten.

Ammonium dimolybdate (ADM) is the inorganic compound with the formula (NH4)2Mo2O7. It is a white, water-soluble solid. ADM is an intermediate in the production of molybdenum compounds from its ores. Roasting typical ore produces crude molybdenum(VI) oxides, which can be extracted into aqueous ammonia, affording ammonium molybdate. Heating solutions of ammonium molybdate gives ADM. Upon heating, solid ammonium dimolybdate decomposes to molybdenum trioxide:


  1. 1 2 3 Haynes, p. 4.77
  2. Haynes, p. 4.134
  3. Åsbrink, S.; Kihlborg, L. and Malinowski, M. (1988). "High-pressure single-crystal X-ray diffraction studies of MoO3. I. Lattice parameters up to 7.4 GPa". J. Appl. Cryst. 21: 960–962. doi:10.1107/S0021889888008271.CS1 maint: Multiple names: authors list (link)
  4. Haynes, p. 5.15
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  7. 1 2 Molybdite Mineral Data
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  12. 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 (1): 47–54. doi:10.1016/j.msec.2011.09.010. PMID   23177771.

Cited sources