Ruthenium(IV) oxide

Chembox new
ImageFile = Rutile-unit-cell-3D-balls.png ImageSize = 200px
Name = Ruthenium(IV) oxide
IUPACName = Ruthenium(IV) oxide
Section2 = Chembox Properties
Formula = RuO₂
MolarMass = 133.07 g/mol (anhydrous)
Appearance = Black crystalline solid
Density = 6.97 g/cm³ (solid)
Solubility = insoluble
MeltingPt = 1200^oC (sublimes)
BoilingPt = decomposes
Section7 = Chembox Hazards
ExternalMSDS = [http://www.jmcatalysts.com/pct/pdfs/msds/422.pdf External MSDS]
EUClass = not listed
Section8 = Chembox Related
OtherCpds = RuO₄,RuCl₃

Ruthenium(IV) oxide (RuO₂) is a black chemical compound containing the rare metal ruthenium and oxygen. The most oftenused O₂ catalyst is ruthenium(IV) oxide, however care must be taken since hydrates of this oxide exist. [Mills, A.; "Chem. Sot. Rev.,"1989, "18", 285.]
RuO₂ is generally used as a catalyst in various industrial applications or an electrode in electrochemical processes. RuO₂ is highly reactive with reducing agents, due to its oxidizing properties.

tructure and Physical Properties

Ruthenium(IV) oxide takes on the rutile crystal structure [ Wyckoff, R.W.G.. "Crystal Structures", Vol. 1. Interscience, John Wiley & Sons: 1963.] [Wells, A.F. "Structural Inorganic Chemistry", 4th ed., Oxford: 1975.] , similar to titanium dioxide and several other metal oxides. Due to its structure, ruthenium(IV) oxide easily forms hydrates.

Ruthenium(IV) oxide is a (nearly black) purple crystalline solid at room temperature. The hydrates of RuO₂ have a blue color to them. RuO₂ sublimes at 1200°C under standard conditions (and does not have boiling point). Ruthenium(IV) oxide has a density of about 6970 kg/m³ or 6.970 g/cm³.

Ruthenium oxide has great capacity to store charge when used in aqueous solutions. [ Matthey, Johnson. "Platinum Metals Review." 2002, "46", 3, 105] Average capacities of ruthenium(IV) oxide have reached 650 F/g when in H₂SO₄ solution and annealed at temperatures lower than 200^oC. [ Kim,Il-Hwan; Kim, Kwang-Bum; "Electrochem. Solid-State Lett.," 2001, "4", 5,A62-A64] In attempts to optimise its capacitive properties, prior work has looked at the hydration of ruthenium oxide, its crystallinity and particle size.

The mass percent composition is as follows: Ruthenium 75.96%, Oxygen 24.04%

Ruthenium(IV) oxide is insoluble in water.

Preparation

There are various ways in preparing ruthenium(IV) oxide. The following processes described below are for preparing RuO₂ as a film.

1. The chemical vapor deposition (CVD) of RuO₂ from suitable voltile ruthenium compounds. [ Pizzini, S.; Buzzancae, g.; "Mat. Res. Bull.", 1972, "7", 449-462.]

2. The pyrolysis, or heating of ruthenium halides, suitably deposited on the substrate by spraying on the heated substrate a solution of the halide . The most commonly used halide is ruthenium(III) chloride to form RuO₂.
This technique has in fact been developed by Schafer for the preparationof nearly stoichiometric RuO₂ single crystals. [ Schafer, H., "Z.an.allg. Chem." 1963, "319", 327]
Both process follow the same reaction mechanism:

Ru^+(IV) + O₂ (heat)→ RuO₂
High temperature flashes of heat up to 1500^oC can remove all oxides and contaminants, and form a new oxide layer on the ruthenium.

3. Another way to prepare RuO₂ is through electroplating. Films can be electroplated from a solution of RuCl₃^.xH₂O. Pt gauze was usedas the counter electrode and Ag/AgCl as the reference electrode. [Leea, Se-Hee; Liu, Ping.; "Solid State Ionics" 2003, "165", 217-221.]

Uses

RuO₂ is extensively used for the coating of titanium anodes for the electrolytic production of chlorine and for the preparation of resistors or integrated circuits. [ De Nora,O.; "Chem. Eng. Techn.", 1970, "42", 222.] [Iles, G.S.; "Platinum Met. Rev.", 1967,"11",126.]

Ruthenium(IV) oxide is a versatile catalyst and doping agent. hydrogen sulfide can be split by light by using a photocatalyst of CdS particles doped with ruthenium(IV) oxide loaded with ruthenium dioxide. [ Park, Dae-chul; Baeg, Jin-ook., "U.S. Pat. Appl. Publ.", 2001,6 pp.] This may be useful in the removal of H₂S from oil refineries and from other industrial processes. The hydrogen produced could be used to synthesize ammonia, methanol, and possibly fuel a future hydrogen economy.

Ruthenium (IV) oxide is being used as the main component in the catalyst of the Deacon process which produces chlorine by the oxidation of hydrogen chloride .

Oxidative Catalyst

RuO₂ by itself is a poor catalyst because without the presence of a hydrate its surface area is greatly decreased. To get pure ruthenium(IV) oxide, it needs to be annealed at 900^oC. The best catalyst for electrochemical processes is to have some hydrate present, but not a completely hydrous one. [Mills, A.; Davies, H.; "Inorganica. Chimica. Acta.," 1991, "189", 149-155] RuO₂ can be used as catalyst in multiple reactions. Such noteworthy reactions are the Fischer-Tropsch process and fuel cells.

The related ruthenium (VIII) oxide is also of great importance in catalytic oxidation reactions.

Precautions

Use personal protection equipment when handling. Conditions and substances to avoid are: extreme heat, fire, acids, aqua regia, organic solvents.

ee also

Ruthenium tetroxide

References

External links

* [http://periodic.lanl.gov/elements/44.html Los Alamos National Laboratory – Ruthenium]