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

Abstract

Fe2O3 is recognized as an excellent oxygen carrier for its low cost and high oxygen capacity. However, pure Fe2O3 must be deposited on supports to ensure high reactivity and durability. Here, we proposed several Fe2O3-based oxygen carriers using MgAl2O4, Ce0.8Gd0.2O1.9, and Zr0.8Y0.2O1.9 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. Fe2O3/Ce0.8Gd0.2O1.9 exhibited a superior performance regarding high hydrogen yield and stable trend over 20 cycles at 750 °C. However, hydrogen yield of Fe2O3/Zr0.8Y0.2O1.9 exceeded that of Fe2O3/Ce0.8Gd0.2O1.9 at higher temperatures (850 °C). Characterizations show that Ce0.8Gd0.2O1.9 exhibits the highest oxygen vacancy concentration, which significantly improves the reduction and reoxidation reactions of Fe2O3, thus leading to an enhanced hydrogen yield. However, the interaction between Fe2O3 and Ce0.8Gd0.2O1.9 contributed to the increase in Fe2+ 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 Ce0.8Gd0.2O1.9 to be used as an effective support for Fe2O3 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.