This study reports molten metals (bismuth, indium, and tin) as effective modifiers for iron-based redox catalysts in the context of chemical loopingbased hydrogen production at intermediate temperatures (450−650 °C) from lowcalorific-value waste gas (e.g., blast furnace gas). The effects of the bismuth promoter on both the surface and bulk properties of iron oxides were studied in detail. Transmission electron microscopy and energy-dispersive spectroscopy (TEM-EDS), low-energy ion scattering (LEIS), Raman spectroscopy, and 18 O 2 exchange experiment revealed that the bismuth modifier forms an overlayer covering the bulk iron (oxides), leading to better anti-coking properties compared to reference La 0.8 Sr 0.2 FeO 3 -and Ce 0.9 Gd 0.1 O 2 -supported iron oxides. The Bimodified sample also exhibited improved anti-sintering properties and high redox activity, resulting in a 4-fold increase in oxygen capacity compared to pristine Fe 2 O 3 (28.9 vs 6.4 wt %) under a cyclic redox reaction at 550 °C. Meanwhile, a small amount of bismuth is doped into the iron oxide structure to effectively enhance its redox properties by lowering the oxygen vacancy formation energy (from 3.1 to 2.1 eV) and the energy barrier for vacancy migration, as confirmed by the experimental results and density functional theory (DFT) calculations. Reactive testing indicates that Bi-modified redox catalysts are highly active to convert low-calorific-value waste gases such as blast furnace gas. Our study also indicates that this strategy can be generalized to low-melting-point metals such as Bi, In, and Sn for iron oxide modification in chemical looping processes.
In the chemical looping hydrogen generation (CLHG) system, methane acts as an important reducing gas, whereas iron oxide has poor reactivity with methane, resulting in the inefficiency of the system. Thus, the fundamental reaction behavior between methane and iron oxide is of great importance. In this paper, applying a high/low-weight hourly space velocity technique, the reaction behavior in a dynamically operated packedbed system was investigated based on the outlet gas concentration profiles. As the reduction process proceeded, complete oxidation, partial oxidation, and methane decomposition dominated in sequence. The results also validated that the CO/CO 2 relative mole fractions followed the equilibrium diagrams of the Fe−C−O system. The reaction behavior in the packed-bed reactor was a combination of thermodynamic limitation and the reaction front movement. This study suggested that the deep reduction CLHG technology is suitable for increasing the conversion of CH 4 in the packed-bed system.
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