Effect of support on hydrogen generation over iron oxides in the chemical looping process

Fe(2)O(3) is recognized as an excellent oxygen carrier for its low cost and high oxygen capacity. However, pure Fe(2)O(3) must be deposited on supports to ensure high reactivity and durability. Here, we proposed several Fe(2)O(3)-based oxygen carriers using MgAl(2)O(4), Ce(0.8)Gd(0.2)O(1.9), and Zr(0.8)Y(0.2)O(1.9) as supports and investigated their performance for chemical looping hydrogen generation. The support effect on chemical looping hydrogen generation performance was evaluated, and the fundamental insights were investigated in depth. Fe(2)O(3)/Ce(0.8)Gd(0.2)O(1.9) exhibited a superior performance regarding high hydrogen yield and stable trend over 20 cycles at 750 °C. However, hydrogen yield of Fe(2)O(3)/Zr(0.8)Y(0.2)O(1.9) exceeded that of Fe(2)O(3)/Ce(0.8)Gd(0.2)O(1.9) at higher temperatures (850 °C). Characterizations show that Ce(0.8)Gd(0.2)O(1.9) exhibits the highest oxygen vacancy concentration, which significantly improves the reduction and reoxidation reactions of Fe(2)O(3), thus leading to an enhanced hydrogen yield. However, the interaction between Fe(2)O(3) and Ce(0.8)Gd(0.2)O(1.9) contributed to the increase in Fe(2+) concentration, thus decreasing the oxygen capacity during the redox cycle and contributing to the declined hydrogen yield at higher temperatures. This work highlights the potential of Ce(0.8)Gd(0.2)O(1.9) to be used as an effective support for Fe(2)O(3) at mid-temperatures. We hope that the support effect in this work can be extended to design and select more active and durable oxygen carriers.