Dopant Modified Iron Based Oxygen Carriers for Chemical Looping Combustion and Gasification Applications (Invited)

Chemical looping technology is promising in high efficiency clean carbonaceous fuel conversion, including chemical looping gasification and chemical looping combustion. The reactions in chemical looping involve cyclic redox reactions with metal oxide as the oxygen carriers to provide lattice oxygen and regenerate in air. Iron-based oxygen carriers modified with both isovalent and aliovalent transition metal ions have been investigated in this work. Isovalent dopants can lower fuel conversion reaction energy barriers by providing active sites for fuel activation and conversion during redox reactions whereas aliovalent dopants can not only provide such active sites but also create Schottky defects to increase the ionic conductivity in the oxygen carriers. In this study, we examine the impact of both isovalent and aliovalent dopants on iron oxide oxygen carriers reactivity and conversion rates using methane reforming and CO combustion as examples. A screen of suitable transition metal ion dopants have been done by DFT calculation as well as experiments. A detailed characterization and reaction mechanism will be discussed. The understanding of the reaction mechanism provides insight into dopant modification for improving the reactivity and recyclability of oxygen carriers, which is essential in commercialization of the oxygen carriers for chemical looping gasification and combustion.