Two-step thermochemical cycles for CO2 splitting on Zr-doped cobalt ferrite supported on silica

Silica-supported Zr-doped cobalt ferrite complex oxides, Co1−2xZrxFe2O4/SiO2 (0 ⩽ x ⩽ 0.15) were prepared via a simple sol-gel auto-combustion method using aqueous silica colloid as the silica source. The products were used as reactive materials in two-step thermochemical cycles for CO2 splitting. Compared to undoped cobalt ferrite, the Zr-doped ones can significantly enhance the rates of the reduction and oxidation steps as well as the yields of CO. The Zr-doped sample also showed greater recyclability than the undoped one. When the sample Co0.8Zr0.1Fe2O4/SiO2 was used as reactive material, the average production of 24.4 mL/gferrite for O2 and 40.2 mL/gferrite for CO were obtained after 20 cycles at 1400 and 1100 °C respectively. A kinetic analysis indicated the apparent activation energy in the CO2 splitting step over Co0.8Zr0.1Fe2O4/SiO2 is 118.0 ± 1.2 kJ/mol, while it is 133.0 ± 2.1 kJ/mol for CoFe2O4/SiO2.