Improving the Reactivity and Stability of Fe<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> in Chemical Looping Process by Optimizing the Al<sub>2</sub>O<sub>3</sub> Precursor
Zixiang Gao, Di Wu, M.A. Barakat, Liyan Sun, Feng Gong, Rui Xiao
Abstract
Oxygen carriers (OCs) with high reactivity and stability are eagerly desired in the chemical looping process to achieve efficient oxygen transfer among different reductants. Al 2 O 3 is a widely used support in preparing Fe 2 O 3 -based OCs due to its low cost and adjustable texture. Also, diverse performances were obtained for the Fe 2 O 3 –Al 2 O 3 synthesized with different Al 2 O 3 precursors; however, how the Al 2 O 3 type influences the performance of Fe 2 O 3 -based OCs is still unclear, which confuses the choice of Al 2 O 3 in preparing the OCs. In the present work, seven types of Al 2 O 3 precursors were adopted to prepare the Fe 2 O 3 –Al 2 O 3 by mechanical mixing, then the reactivity and stability of these OCs were assessed in a chemical looping hydrogen generation process, and the way Al 2 O 3 affects the performance of OCs was analyzed via XRD, SEM, BET, TPR, and XPS analysis on the calcined Al 2 O 3 precursors and the prepared OCs. Results showed that the high reactivity of Fe 2 O 3 –Al 2 O 3 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 Fe 2 O 3 –Al 2 O 3 OCs with high surface area and pore volume achieved nearly 100% fuel conversion, meanwhile produced a higher yield of H 2 (1.6 mmol/g Fe 2 O 3 ), and showed a stable behavior in cycling tests. Furthermore, compared to other properties of the Al 2 O 3 -supported OCs, we found that the solubility of Al 2 O 3 in Fe 2 O 3 is the dominant factor that affects the hercynite formation during the Fe 2 O 3 –Al 2 O 3 reduction process.