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 °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 °C and 1000 °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 °C and 1000 °C, respectively. Ba₃Fe₂O₆ also exhibits excellent recyclability and satisfactory chemical looping oxygen uncoupling (CLOU) activity over temperature swing cycles between 550 °C and 950 °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.