Chemical insights on the activity of La1-xSrxFeO3 perovskites for chemical looping reforming of methane coupled with CO2-splitting

Coupling Chemical Looping Reforming of methane with CO2-splitting reactions represents an attractive route to achieve continuous syngas and CO productivities with reduced carbon footprint in a cyclic two-steps process. Both reactions are performed in the presence of a metal oxide, which switches from reduced to oxidized in successive stages. In this work, La1-xSrxFeO3 perovskites were selected, because the Sr/La ratio can be varied to tune the redox capacity of the system. Reactivity of these materials were tested in isothermal cycles at 850 degrees C with the aim of simultaneously maximize the conversion of CH4 and ensure the re-oxidation of the solid. Although the highest redox capacity is observed for the material with higher Sr-content (x = 0.9), the best performance is obtained for La0.9Sr0.1FeO3, which exhibits notable overall syngas yields per cycle: 12.8 mmol H-2 g(-1) and 15.9 mmol CO g(-1). Analyses of the reactivity of these perovskites reveal the important contribution of both methane cracking and Boudouard reaction on the production of syngas, particularly for materials with low Sr/La ratio. These two processes operate, respectively, in the reduction and oxidation stages, in such a way that a significant deactivation of the perovskites by carbon deposition is avoided. These findings highlight the influence of aspects other than redox properties on the high temperature reactivity of La1-xSrxFeO3 perovskites in cycles alternating CH4 and CO2. On the other hand, materials with high La/Sr ratio experienced significant changes in the phase composition after prolonged reduction in CH4. Nevertheless, these transformations are reversible and, after re-oxidation, the recovered perovskite remains highly active, emphasizing the stability of these reactive solids.