Cerium(IV) oxide–cerium(III) oxide cycle
# Cerium(IV) oxide–cerium(III) oxide cycle

The cerium(IV) oxide–cerium(III) oxide cycle or $CeO_2/Ce_2O_3$ cycle is a two-step thermochemical process that employs cerium(IV) oxide and cerium(III) oxide for hydrogen production. The cerium-based cycle allows the separation of $H_2$ and $O_2$ in two steps, making high-temperature gas separation redundant.

## Process description

The thermochemical two-step water splitting process (thermochemical cycle) uses redox systems:

* Dissociation: $2CeO_2$ → $Ce_2O_3$ + 0.5 $O_2$
* Hydrolysis: $Ce_2O_3$ + $H_2O$ → $2CeO_2$ + $H_2$

For the first endothermic step, cerium(IV) oxide is thermally dissociated in an inert gas atmosphere at 2,000 °C (3,630 °F) and 100-200 mbar into cerium(III) oxide and oxygen. In the second exothermic step cerium(III) oxide reacts at 400 °C (752 °F)–600 °C (1,112 °F) in a fixed bed reactor with water and produces hydrogen and cerium(IV) oxide.

