Perovskite Promoted Mixed Cobalt-Iron Oxides for Enhanced Chemical Looping Air Separation

Chemical looping air separation (CLAS) is a promising approach to produce high purity oxygen from air. Redox kinetics and oxygen carrying capacity of oxide-based oxygen carrier materials play a critical role in the overall performance of CLAS. In view of the fast lattice oxygen transport property of mixed-conductive perovskite materials, composites of La0.8Sr0.2CoxFe1-xO3 (LSCF) perovskite and mixed Co-Fe oxides (CF) were investigated for chemical looping air separation. The effects of Fe and perovskite addition were systematically examined by varying Co/Fe and LSCF/CF ratios. Increase of Fe in mixed Co-Fe oxides significantly increases oxidation kinetics of LSCF-CF composites while decreasing the rate of oxygen release. An optimized average redox rate was achieved by balancing the oxygen uptake (oxidation) and release (reduction) rates through tuning Co/Fe ratio, with the maximum occurring at a ratio of 9:1. Unpromoted Co-Fe mixed oxide exhibited a working oxygen capacity of 1.6 wt.% at 850 degrees C. With the addition of 10-30 wt % LSCF, the oxygen capacity more than doubled to 4.1-4.2%. The enhanced oxygen storage/release is attributed to well dispersed Co-Fe mixed oxide within LSCF, which assists fast lattice oxygen diffusion to and from Co-Fe mixed oxide. The LSCF-CF composite exhibited satisfactory stability and activity over 50 redox cycles at 850 degrees C.