Characterization of Two-Step Tin-Based Redox System for Thermochemical Fuel Production from Solar-Driven CO2 and H2O Splitting Cycle

The solar thermochemical dissociation of H 2 O and CO 2 for renewable fuel production from two-step SnO 2 /SnO cycle is considered. This cycle is based on the solar production of SnO phase in a first endothermic step that is subsequently used for splitting CO 2 and H 2 O in a second exothermic step. The reactivity of tin-based species was studied in order to elucidate the phenomena occurring during its heating and subsequent reoxidation in a H 2 O or CO 2 atmosphere to produce H 2 or CO. Two main types of reactant were considered for comparing their reactivity: SnO nanopowder obtained via solar sublimation and condensation of commercial SnO powder, and Sn/SnO 2 nanopowder obtained via disproportionation of nanosized SnO. The reaction rate was quantified via thermogravimetry analysis and the reaction products were characterized using Mössbauer spectrometry and X-ray diffraction. The SnO and Sn/SnO 2 nanopowders are more reactive with H 2 O than with CO 2 in the range 550–650 °C. SnO is also more reactive with oxidants than Sn/SnO 2 . The disproportionation reaction starts significantly around 600 °C, giving rise to a particular Sn II phase that reacts faster with the oxidants but is more prone to passivation. A kinetic study yields an activation energy of 101 ± 10 kJ mol –1 and 53 ± 1 kJ mol –1 for the Sn/SnO 2 oxidation with CO 2 and H 2 O, respectively.