Microstructured iron-based spinel oxygen carriers derived from Prussian blue analogues for chemical looping CO2 conversion

Iron oxide is a promising oxygen carrier for chemical looping CO2 conversion, but suffers from easy reactivity deactivation due to particle sintering during redox cycles. Adding other active metals and designing special morphology are two effective pathways to deal with this issue. A series of microstructured iron-based spinel oxygen carriers are synthesized from thermal transformation of Prussian blue analogues (M3[Fe(CN)6]2, M = Co, Ni, Cu) using other active metals to exchange iron position in Prussian blue. Detailed characterization techniques and reactivity experiments are performed to explore the relationship among material structure, cyclic stability and CO yield. All the spinel oxygen carrier are obtained with special morphologies and good reactivity. Due to the different nature of doping metals, Co is helpful to maintain cubic structure while Cu would induce particle aggregation. Co-Fe shows a matched reduction and oxidation rates, while Cu-Fe and Ni-Fe exhibit a higher oxidation and a higher reduction rate, respectively. NiFe-Zr material shows a maximum STYCO of 2.15 mmol·s-1·kgOC-1 with no deactivation. This is ascribed to two aspects: (i) Ni cannot be re-oxidized by CO2 but acts a catalytic site to improve activity, (ii) Fe3O4 rather than NiFe2O4 is preferred to be formed during redox cycles. This work provides a new way to design efficient spinel oxygen carriers for chemical looping CO2 conversion.