Exploring the Redox Behavior of La0.6Sr0.4Mn1−xAlxO3 Perovskites for CO2-Splitting in Thermochemical Cycles

Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La0.6Sr0.4Mn1−xAlxO3 (x = 0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300 °C in inert atmosphere up to 0.32 mmol g−1 of O2 are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x = 0.5, corresponding to an O2 release of 0.318 mmol g−1 (δ = 0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO2 in the oxidation step at 900 °C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La0.6Sr0.4Mn0.6Al0.4O3, with reduction extent of 0.266 mmol g−1, but the production of CO is in comparison significantly lower (0.114 mmol g−1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials.