Solar Syngas Production via H₂O/CO₂-Splitting Thermochemical Cycles with Zn/ZnO and FeO/Fe₃O₄ Redox Reactions

The solar production of syngas from H 2 O and CO 2 is examined via two-step thermochemical cycles based on Zn/ZnO and FeO/Fe 3 O 4 redox reactions. The first, endothermic step is the thermal dissociation of the metal oxide using concentrated solar radiation as the energy source of high-temperature process heat. The second, nonsolar, exothermic step is the reaction of the metal or reduced metal oxide with a mixture of H 2 O and CO 2 yielding syngas (H 2 and CO), together with the initial form of the metal oxide that is recycled to the first step. Chemical equilibrium compositions for the systems of Zn and FeO with CO 2 + H 2 O were computed as a function of temperature and pressure for different stoichiometries. A series of dynamic thermogravimetric experimental runs in the range 673−1423 K was carried out to evaluate the reaction kinetics and syngas quality of the second step. The molar flow rate fractions of the gaseous products exhibited linear dependencies on the molar flow rate fractions of the gaseous reactants for both the FeO/Fe 3 O 4 and Zn/ZnO systems.