Kinetics and mechanism of solar-thermochemical H2 and CO production by oxidation of reduced CeO2

[Display omitted] •Oxidation of reduced ceria with steam or CO2 is carried out.•A laser-assisted stagnation flow reactor is used.•Rigorous data analysis is used to de-convolute experimental transport effects.•Reaction rate kinetic parameters over the entire reaction domain are identified. The combination of high thermal stability and fast reduction/oxidation kinetics has drawn attention to CeO2 for use in solar-driven, two-step thermochemical cycles for water and/or carbon dioxide splitting. In accordance with this renewed interest in CeO2, there is a need to better understand the gas splitting chemistry on the reduced oxide. In this study, we measured the H2 production rates over ceria powder, thermally reduced by laser irradiation, during oxidation by H2O and CO2 gases in a stagnation flow reactor. The reaction kinetics was extracted using a model-based analytical approach to account for the effects of mixing and dispersion in the reactor. We find the rigor of this approach necessary in order to identify the rate controlling mechanism and assign parameters to the kinetic model, and to successfully model the production of H2 and CO production over the entire envelope of the fuel curve. The water splitting reaction, in the range of 750–950 °C and 20–40 vol% H2O, can best be described by a first-order kinetic model with low apparent activation energy (29 kJ/mol); while the carbon dioxide splitting reaction, in the range of 650–875 °C and 10–40 vol% CO2, is a more complex surface-mediated phenomena.