CO2 valorisation based on Fe3O4/FeO thermochemical redox reactions using concentrated solar energy

The solar‐driven dissociation of CO₂ by thermochemical looping via Fe₃O₄/FeO redox reactions is considered. The process recycles and upgrades CO₂ to ultimately produce chemical synthetic fuels from high‐temperature solar heat and abundant feedstock as only inputs. The two‐step process encompasses the endothermic reduction of Fe₃O₄ to FeO and O₂ using concentrated solar energy as the high‐temperature source for reaction enthalpy and the nonsolar exothermic oxidation of FeO with CO₂ to generate CO. The resulting Fe₃O₄ is then recycled to the first step and carbon monoxide can be further processed to syngas and serve as the building block to synthesise various synfuels by catalytic processes. This study examines the thermodynamics and kinetics of the pertinent reactions. The high‐temperature thermal reduction of Fe₃O₄ is realised above the oxide melting point by using concentrated solar thermal power. The reactivity of the synthesised FeO‐rich material with CO₂ at moderate temperature is then investigated by thermogravimetry. FeO conversion higher than 90% can be achieved with reaction rates depending on temperature, particle size and CO₂ concentration. The solar‐produced nonstoichiometric FeO is more reactive with CO₂ than commercial pure FeO. Activation energies of 57 and 68 kJ/mol are derived from a kinetic analysis of the CO₂‐splitting reaction in the range of 600 °C to 800 °C with solar and commercial FeO, respectively. Copyright © 2012 John Wiley & Sons, Ltd.