Ruthenium(IV) oxide
Encyclopedia
Ruthenium oxide (Ru
O2
) 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.
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.
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:
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 RuCl3.xH2O. Pt gauze was used
as the counter electrode and Ag/AgCl as the reference electrode.
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.
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.
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
O2
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
) is a black chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
containing the rare metal ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. 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
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
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 rutileRutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
crystal structure, similar to titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
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
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
(CVD) of RuO2 from suitable volatile ruthenium compounds.
2. The pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
, 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
Ruthenium(III) chloride
Ruthenium chloride is the chemical compound with the formula RuCl3. "Ruthenium chloride" more commonly refers to the hydrate RuCl3·xH2O. Both the anhydrous and hydrated species are dark brown or black solids...
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+(IV) + 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
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
. Films can be electroplated from a solution of RuCl3.xH2O. 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
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
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
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
.
Ruthenium (IV) oxide is being used as the main component in the catalyst of the Deacon process
Deacon process
The Deacon process was a secondary process used during the manufacture of alkalis by the Leblanc process. Hydrogen chloride gas was converted to chlorine gas which was then used to manufacture a commercially valuable bleaching powder, and at the same time the emission of waste hydrochloric acid...
which produces chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
by the oxidation of hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
.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 annealedAnnealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
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
Fischer-Tropsch process
The Fischer–Tropsch process is a set of chemical reactions that convert a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. The process, a key component of gas to liquids technology, produces a petroleum substitute, typically from coal, natural gas, or biomass for use as synthetic...
and fuel cells.