第二届中国化学链会议

Al2O3 is a widely used support in preparing Fe2O3-based oxygen carriers (OCs) due to its low cost and adjustable texture. Yet various Fe2O3­-Al2O3 synthesized with different Al2O3 precursors (such as α-Al2O3, γ-Al2O3, β-Al2O3, and hydrate nitrate of Al, etc.) and preparation methods (mechanical mixing, sol-gel, impregnation, etc.) have been reported in multiple chemical looping process, correspondingly diverse performances were presented, whereas mechanisms of how Al2O3 influencing the performance of Fe2O3-based OCs are insufficient, which causes a confusion in choosing Al2O3. In the present work, five 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 chemical looping hydrogen generation process in a fixed bed reactor. Results showed that pure Fe2O3 and Fe2O3-­inert Al2O3 have a low reactivity with CH4, while Fe2O3 supported by the Al2O3 from AlOOH, activated Al2O3 and Al(OH)3 present high reactivity achieving nearly 100% biomass gasified gases conversion. X-ray diffraction (XRD), scanning electronic microscope (SEM) and micro texture analysis on the calcined Al2O3 precursors and as-prepared OCs revealed that various crystalline phases possessed for the calcined Al2O3 precursors, and close relationship exists between these calcined Al2O3 precursors and Fe2O3-based OCs in micro photograph, BET surface area and pore volume. Despite the fact that α-Al2O3 supported Fe2O3-based OCs presented low CO2 selectivity and low H2 yield, these Fe2O3-based OCs with high BET surface area and pore volume, such as Fe2O3­-AlOOH and Fe2O3-activated Al2O3, produced high purity CO2 and high production of H2, and showed a stable behavior in cycling tests compared with other Fe2O3-based OCs. Finally, the mechanism of Al2O3 influencing the performance of Fe2O3-based OCs was discussed from the perspective of lattice oxygen diffusion and micro texture effects.
 

Al2O3; Methane; Chemical Looping; Hydrogen; Hercynite