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Original article (peer-reviewed)

Volume (Issue) 24
Page(s) 2716 - 2722
Title of proceedings ENERGY & FUELS
DOI 10.1021/ef901544v


Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on Zn/ZnO and FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of ZnO to Zn or Fe3O4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO2 and H2O with Zn or FeO to CO and H2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with Zn in the range 673 – 748 K and CO2/H2O concentrations of 2.5-15% in Ar, and for reactions with FeO in the range 973 – 1273 K and CO2/H2O concentrations of 15-75% in Ar. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reactions based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.