Improving the Reactivity and Stability of Fe2O3/Al2O3 in Chemical Looping Process by Optimizing the Al2O3 Precursor

Oxygen carriers (OCs) with high reactivity and stability are eagerly desired in the chemical looping process to achieve efficient oxygen transfer among different reductants. Al2O3 is a widely used support in preparing Fe2O3-based OCs due to its low cost and adjustable texture. Also, diverse performances were obtained for the Fe2O3–Al2O3 synthesized with different Al2O3 precursors; however, how the Al2O3 type influences the performance of Fe2O3-based OCs is still unclear, which confuses the choice of Al2O3 in preparing the OCs. In the present work, seven types of Al2O3 precursors were adopted to prepare the Fe2O3–Al2O3 by mechanical mixing, then the reactivity and stability of these OCs were assessed in a chemical looping hydrogen generation process, and the way Al2O3 affects the performance of OCs was analyzed via XRD, SEM, BET, TPR, and XPS analysis on the calcined Al2O3 precursors and the prepared OCs. Results showed that the high reactivity of Fe2O3–Al2O3 originated from the improved internal diffusion and high oxygen deficiency and adsorbed oxygen content. Furthermore, structure–activity correlation analysis implied that the microtexture plays a bigger role in the OC reactivity and stability when compared with other physical characteristics, and the Fe2O3–Al2O3 OCs with high surface area and pore volume achieved nearly 100% fuel conversion, meanwhile produced a higher yield of H2 (1.6 mmol/g Fe2O3), and showed a stable behavior in cycling tests. Furthermore, compared to other properties of the Al2O3-supported OCs, we found that the solubility of Al2O3 in Fe2O3 is the dominant factor that affects the hercynite formation during the Fe2O3–Al2O3 reduction process.