Reducible Supports for Ni-based Oxygen Carriers in Chemical Looping Combustion

Chemical Looping Combustion (CLC) is an emerging clean combustion technology for combustion of fossil fuels with inherent CO2 capture. In the present work, we investigate the use of reducible oxides (CeO2, La2O3) as oxygen carriers and as supports for nickel as active metal using TGA and fixed-bed reactor studies. Although CeO2 demonstrates reducibility (delta approximate to 8% at 800 degrees C with H-2) compared to minimal reducibility for La2O3, the oxygen carrying capacity is negligible compared to typical metals. However, ceria has a pronounced effect if used as support for Ni as oxygen carrier: In a comparison of reducible vs conventional, nonreducible oxide supports (Al2O3, SiO2), all carriers show thermal stability in TGA with H-2 as fuel but only reducible supports allow for complete carrier conversion (vs similar to 83% for Ni-Al2O3 with H-2 and similar to 75% with CH4 as fuel at 800 degrees C). Furthermore, the oxidation and reduction kinetics are accelerated, and the window for efficient total oxidation is strongly enlarged when using ceria supports. Overall, these results indicate significant potential for improved redox properties of oxygen carriers in CLC through a synergistic effect between metals and reducible oxides supports.