Investigation of barium iron oxides for CO2 capture and chemical looping oxygen uncoupling

The performance of two underexploited ternary oxides - Ba3Fe2O6 and Ba5Fe2O8 are investigated for carbon dioxide capture and chemical looping oxygen uncoupling. The ternary compound Ba3Fe2O6 was found to have a structure characterised by space group Pa3. Experimental results have shown that both Ba3Fe2O6 and Ba5Fe2O8 are capable of cyclically capturing CO2 at temperatures above 800 degrees C. Ba5Fe2O8 demonstrated superior CO2 capture performance compared to Ba3Fe2O6, with consistent gravimetric CO2 uptake capacities of 4.35 wt% and 13.39 wt% at 900 degrees C and 1000 degrees C, respectively, over 20 cycles. In comparison, Ba3Fe2O6 demonstrated high initial CO2 uptake capacities which deteriorated cyclically, with 20 cycle average capacities of 7.73 wt% and 11.99 wt% at 900 degrees C and 1000 degrees C, respectively. Ba3Fe2O6 also exhibits excellent recyclability and satisfactory chemical looping oxygen uncoupling (CLOU) activity over temperature swing cycles between 550 degrees C and 950 degrees C. In contrast, the strong affinity with CO2 makes Ba5Fe2O8 unsuitable for application in chemical looping oxygen uncoupling or chemical looping air separation, especially in the presence of substantial partial pressures of CO2.