Solar Syngas Production From H2O and CO2 via Two Step Thermochemical Cycles Based on FeO/Fe3O4 Redox Reactions: Kinetic Analysis

Abstract

Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe3O4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO2 and H2O with 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 FeO in the range 973–1273 K and CO2/H2O concentrations of 15–75%. 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 reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.