Cerium(III) oxide
# Cerium(III) 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 $Ce_2O_3$ and is gold-yellow in color.

## Applications

### Engine and exhaust catalysts

Cerium oxide is used as a 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 is reduced by carbon monoxide to cerium(III) oxide:

    2 $CeO_2$ + CO → $Ce_2O_3$ + $CO_2$

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

    2 $Ce_2O_3$ + $O_2$ → 4 $CeO_2$

Major automotive applications for cerium(III) oxide are as a catalytic converter for the oxidation of CO and $NO_x$ emissions in the exhaust gases from motor vehicles, and secondly, cerium oxide finds use as a fuel additive to diesel fuels, which results in increased fuel efficiency and decreased hydrocarbon derived particulate matter emissions, however the health effects of the cerium oxide bearing engine exhaust is a point of study and dispute.

### Water splitting

The cerium(IV) oxide–cerium(III) oxide cycle or $CeO_2/Ce_2O_3$ cycle is a two step thermochemical water splitting process based on cerium(IV) oxide and cerium(III) oxide for hydrogen production.

### 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. This combination of cerium(III) oxide and tin(II) oxide is rare, and obtained only with difficulty on a laboratory scale.

## 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.

