Redox kinetics of ceria–zirconia (Ce1−xZrxO2−δ) for thermochemical partial oxidation of methane and H2O/CO2 splitting at moderate temperature

Abstract

Solar-driven thermochemical H₂O splitting (STWS) and CO₂ splitting (STCDS) processes represent highly efficient methods for achieving widespread and efficient conversion and storage of solar energy. The synergistic decomposition of H₂O and CO₂ by methane with cerium–zirconium oxides has been demonstrated to be an effective strategy to keep the reaction isothermal and increase its conversion efficiency. The kinetic behavior and mechanisms during redox cycling play a crucial role in optimizing solar thermochemical processes. The present research involved synthesizing cerium–zirconium oxides (Ce_1−xZr_xO₂, x = 0–0.4) with varying Zr⁴⁺ doping levels using a co-precipitation method. The kinetic behaviors of these compounds were then studied in the context of partial oxidation of CH₄ and the H₂O/CO₂ splitting processes at temperatures ranging from 800 to 950 °C in a bench-scale fixed bed. The research results indicate that the gas production from the oxidation–reduction reaction significantly increases after Zr⁴⁺ doping. The POx of CH₄ and H₂O/CO₂ splitting can be described by using the zero-order contraction model and the nucleation model, respectively. Compared to CO₂, H₂O more readily occupies the oxygen vacancies in reduced Ce_1−xZr_xO₂, thereby facilitating the generation of a greater amount of H₂ and CO in the redox cycle.