(31d) CO2 Conversion Via RWGS-CL over La-Perovskite Oxide with Three Metals (Co, Fe, and Mn) in the B-Site

Carbon dioxide (CO₂) is one of the major greenhouse gases contributing to climate change. Countries around the world have already committed to reduce CO₂ emissions, for which it is imperative to develop CO₂ reduction technologies that are economically feasible. Reverse water gas shift – chemical looping (RWGS-CL) uses perovskite oxides of the form ABO₃ to convert CO₂ to carbon monoxide (CO), which can be converted to liquid fuels. First the perovskite is reduced using hydrogen (H₂) forming an oxygen vacant perovskite ABO_3-δ, subsequently CO₂ oxidizes the perovskite, regenerating the material and producing CO. Perovskite oxides are stable and can be used over several cycles. It has been shown in previous studies that cobalt (Co), iron (Fe), and manganese (Mn) have individual properties that facilitate CO₂ conversion. Here we show the CO₂ conversion performance of a La-perovskite with varying composition of the three metals in the B-site. Four compositions of LaCo_xFe_yMn_1-x-yO₃ were studied; Co-rich (x=0.5), Fe-rich (y=0.5), Mn-rich (x=y=0.25), and equal composition (x=y=0.33). Bulk oxygen vacancy formation energies (E_vac) were performed using density functional theory (DFT) via the Vienna ab-initio Simulation Package (VASP-5.3.3). The four compositions had E_vac within the range which has been reported leads to favorable CO₂ conversion. The Co and Fe-rich perovskites performed better, as predicted from E_vac calculations, producing 1786 µmol CO/g and 1431 µmol CO/g respectively. These results compare favorable to previous results in which two cations were used on both the A and B sites.