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Ruthenium(IV) oxide

Names
IUPAC name Ruthenium(IV) oxide
Other names Ruthenium dioxide
Identifiers
CAS Number	12036-10-1
ECHA InfoCard	100.031.660
CompTox Dashboard (EPA)	DTXSID0065193
Properties
Chemical formula	RuO2
Molar mass	133.07 g/mol
Appearance	blue-black solid
Density	6.97 g/cm
Boiling point	1200 °C subl.
Solubility in water	insoluble
Structure
Crystal structure	Rutile (tetragonal), tP6
Space group	P42/mnm, No. 136
Coordination geometry	Octahedral (Ru); trigonal planar (O)
Hazards
Flash point	Non-flammable
Related compounds
Other anions	Ruthenium disulfide
Other cations	Osmium(IV) oxide
Supplementary data page
Ruthenium(IV) oxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Ruthenium(IV) oxide (RuO₂) is a black chemical compound containing the rare metal ruthenium and oxygen. The most often used O₂ catalyst is ruthenium(IV) oxide, however care must be taken since hydrates of this oxide exist.

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.

Structure and physical properties

Ruthenium(IV) oxide takes on the rutile crystal structure, 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.

Ruthenium oxide has great capacity to store charge when used in aqueous solutions. Average capacities of ruthenium(IV) oxide have reached 650 F/g when in H₂SO₄ solution and annealed at temperatures lower than 200 °C. In attempts to optimise its capacitive properties, prior work has looked at the hydration of ruthenium oxide, its crystallinity and particle size.

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 volatile ruthenium compounds.

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 preparation of nearly stoichiometric RuO₂ single crystals.

Both process follow the same reaction mechanism:

Ru + O₂ (heat)→ RuO₂

High temperature flashes of heat up to 1500 °C 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 RuCl₃xH₂O. Pt gauze was used as the counter electrode and Ag/AgCl as the reference electrode.

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.

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. 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.It can be also used as active material in supercapacitor because has very high charge transfer capability.

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 °C. The best catalyst for electrochemical processes is to have some hydrate present, but not a completely hydrous one. RuO₂ can be used as catalyst in multiple reactions. Such noteworthy reactions are the Fischer-Tropsch process and fuel cells.

References

1. Mills, A.; Chem. Sot. Rev.,1989, 18, 285.
2. Wyckoff, R.W.G.. Crystal Structures, Vol. 1. Interscience, John Wiley & Sons: 1963.
3. Wells, A. F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press
4. Matthey, Johnson. Platinum Metals Review. 2002, 46, 3, 105
5. Kim,Il-Hwan; Kim, Kwang-Bum; Electrochem. Solid-State Lett., 2001, 4, 5,A62-A64
6. Pizzini, S.; Buzzancae, g.; Mat. Res. Bull., 1972, 7, 449-462.
7. Schafer, H., Z.an.allg. Chem. 1963, 319, 327
8. Lee, Se-Hee; Liu, Ping.; Solid State Ionics 2003, 165, 217-221.
9. De Nora,O.; Chem. Eng. Techn., 1970, 42, 222.
10. Iles, G.S.; Platinum Met. Rev., 1967,11,126.
11. Park, Dae-chul; Baeg, Jin-ook., U.S. Pat. Appl. Publ., 2001,6 pp.
12. Mills, A.; Davies, H.; Inorganica. Chimica. Acta., 1991, 189, 149-155

External links

• Los Alamos National Laboratory – Ruthenium

• Oxides
• Ruthenium compounds