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 H2O and CO, for renewable fuel production from two-step SnO2/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 CO2 and H2O 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 H2O or CO2 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/SnO2 nanopowder obtained via disproportionation of nanosized SnO. The reaction rate was quantified via thermogravimetry analysis and the reaction products were characterized using Mossbauer spectrometry and X-ray diffraction. The SnO and Sn/SnO2 nanopowders are more reactive with H2O than with CO2 in the range 550-650 degrees C. SnO is also more reactive with oxidants than Sn/SnO2. The disproportionation reaction starts significantly around 600 degrees 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/SnO2 oxidation with CO2 and H2O, respectively.