Cerium(III) oxide

For the other compound also known as cerium oxide, see Cerium(IV) oxide.

Cerium(III) oxide, also known as cerium oxide, cerium trioxide, cerium sesquioxide, cerous oxide or dicerium trioxide, is an oxide of the rare-earth metal cerium. It has chemical formula Ce₂O₃ and is gold-yellow in color. According to X-ray crystallography, the Ce(III) ions are seven-coordinate, a motif typical for other trivalent lanthanide oxides.^[1]

Cerium(III) oxide

Cerium(III) oxide
Names
IUPAC name Cerium(III) oxide
Other names Cerium sesquioxide
Identifiers
CAS Number	1345-13-7 Y
3D model (JSmol)	Interactive image
ChemSpider	8081132
ECHA InfoCard	100.014.289
EC Number	234-374-3
PubChem CID	9905479
UNII	82Q2098IFG
CompTox Dashboard (EPA)	DTXSID60149580
InChI InChI=1S/2Ce.3O/q2*+3;3*-2 Key: DRVWBEJJZZTIGJ-UHFFFAOYSA-N
SMILES [O-2].[O-2].[O-2].[Ce+3].[Ce+3]
Properties
Chemical formula	Ce2O3
Molar mass	328.229 g·mol−1
Appearance	yellow-green dust[citation needed]
Density	6.2 g/cm3
Melting point	2,177 °C (3,951 °F; 2,450 K)
Boiling point	3,730 °C (6,750 °F; 4,000 K)
Solubility in water	insoluble
Solubility in sulfuric acid	soluble
Solubility in hydrochloric acid	insoluble
Structure
Crystal structure	Hexagonal, hP5
Space group	P3m1, No. 164
Hazards
GHS labelling:
Pictograms
Related compounds
Other anions	Cerium(III) chloride
Other cations	Lanthanum(III) oxide, Praseodymium(III) oxide
Related compounds	Cerium(IV) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Applications

Cerium oxide is of commercial interest as a catalyst for oxidation of carbon monoxide and reduction of NO_x. These applications exploit the facility of the Ce(III)/Ce(IV) redox couple.^[2] It is used in catalytic converters ("three-way catalytic converter") for the minimisation of CO emissions in the exhaust gases from motor vehicles. When there is a shortage of oxygen, cerium(IV) oxide oxidizes carbon monoxide to the benign dioxide:^[3][4]

2 CeO₂ + CO → Ce₂O₃ + CO₂

When oxygen is in surplus, the process is reversed and cerium(III) oxide is oxidized to cerium(IV) oxide:

2 Ce₂O₃ + O₂ → 4 CeO₂

Cerium oxide-based catalysts have been intensively investigated for selective catalytic reduction (SCR) of NO_x. Such technologies, which tend to use vanadium oxide-based catalysts rather than ceria, are associated with power plants, foundries, cement factories and other energy-intensive facilities.^[5]

Cerium oxide finds use as a fuel additive to diesel fuels,^{[clarification needed]} which results in increased fuel efficiency and decreased hydrocarbon derived particulate matter emissions,^[6] however the health effects of the cerium oxide bearing engine exhaust is a point of study and dispute.^[7][8][9]

Other properties

Water splitting

The cerium(IV) oxide–cerium(III) oxide cycle or CeO₂/Ce₂O₃ cycle is a two step thermochemical water splitting process based on cerium(IV) oxide and cerium(III) oxide for hydrogen production.^[10][2]

Photoluminescence

Cerium(III) oxide combined with tin(II) oxide (SnO) in ceramic form is used for illumination with UV light. It absorbs light with a wavelength of 320 nm and emits light with a wavelength of 412 nm.^[11] This combination of cerium(III) oxide and tin(II) oxide is rare, and obtained only with difficulty on a laboratory scale.^{[citation needed]}

Production

Cerium(III) oxide is produced by the reduction of cerium(IV) oxide with hydrogen at approximately 1,400 °C (2,550 °F). Samples produced in this way are only slowly air-oxidized back to the dioxide at room temperature.^[12]