Selective CO_2 deoxygenation to CO in chemically looped reverse water–gas shift using iron-based oxygen carrier

Chemical-looped reverse water–gas shift reaction was investigated using transition metal/metal oxides as oxygen carriers. Iron is identified as the only promising oxygen carrier that shows compelling CO _ 2 splitting reactivity. A chemically looped reverse water–gas shift reaction was developed using an iron-based oxygen carrier. Compared with conventional catalytic conversion processes, the chemical looping method has the advantage of high selectivity and cheap materials cost due to the separation of CO_2 splitting and H_2 oxidation half-reactions that are enabled by earth-abundant transition metal oxygen carriers. However, for such process to be economically attractive, the operation temperature should ideally be low enough such that low-grade industrial waste heat can be utilized. In other words, the reactivity of oxygen carriers toward the aforementioned half-reactions is most critical. To address the materials challenge, four transition metal-based oxygen carriers, i.e., iron, nickel, manganese, and copper, are studied using temperature-programmed techniques under H_2 and CO_2. Iron is identified to be the only oxygen carrier reactive toward CO_2 splitting and capable of completing the redox cycle at 450 °C with 100% reverse water–gas shift selectivity. Although the thermal stability of the iron oxygen carriers shows room for improvement, our work demonstrates the great potential of a scalable and economically viable route for CO_2 conversion that is compatible with current industrial processes. Graphical abstract