Selective CO2 deoxygenation to CO in chemically looped reverse water–gas shift using iron-based oxygen carrier

Abstract

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 CO2 splitting and H2 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 H2 and CO2. Iron is identified to be the only oxygen carrier reactive toward CO2 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 CO2 conversion that is compatible with current industrial processes.Graphical abstract