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

The cerium(IV) oxide–cerium(III) oxide cycle or CeO2/Ce2O3 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 H2 and O2 in two steps, making high-temperature gas separation redundant.

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


 * Dissociation: 2CeO2 → Ce2O3 + 0.5 O2
 * Hydrolysis: Ce2O3 + H2O → 2CeO2 + H2

For the first endothermic step, cerium(IV) oxide is thermally dissociated in an inert gas atmosphere at 2000 °C and 100-200 mbar into cerium(III) oxide and oxygen. In the second exothermic step cerium(III) oxide reacts at 400 °C–600 °C in a fixed bed reactor with water and produces hydrogen and cerium(IV) oxide.