Liquid Metal Shell as an Effective Iron Oxide Modifier for Redox-Based Hydrogen Production at Intermediate Temperatures

Abstract

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.

Recent progress in liquid metal printing and its applications

“…Liquid metals would be further developed in catalysis, 17 catalytic hydrogen production, 18 and catalytic atom transfer of free radicals. 19 At room temperature, a LM base method is proposed for the catalytically assisted deposition and graphitization of molybdenum dioxide (MoO 2 ) (Fig.…”

“…The chemical cycling of LMs (Bi, In, and Ti) from low calo-ric value exhaust gases (e.g., blast furnace gas) as effective modiers for iron-based redox catalysts has been investigated at moderate temperatures (450-650 °C). 18 The bismuth modier forms a coating layer on the Fe oxide matrix and has better anticoking performance than the Fe oxides supported by La 0.8 Sr 0.2 FeO 3 and Ce 0.9 GD 0.1 O 2 . In the cyclic redox reaction at 550 °C, the sintering resistance and redox activity of bismuth-modied samples were also improved, and the oxygen capacity was 4 times higher than that of the original Fe 2 O 3 (28.9 vs. 6.4 wt%).…”

Ru-promoted perovskites as effective redox catalysts for CO2 splitting and methane partial oxidation in a cyclic redox scheme

“…20,23 Iron/iron oxide redox pairs are commonly used as the redox catalyst. [25][26][27][28][29][30][31][32][33] However, studies have shown that they generally lead to low syngas selectivity and CO 2 conversion. 25,34,35 On the other hand, mixing Fe with other metal oxides has been shown to improve redox properties.…”

“…[54][55][56] Although tremendous efforts have been made in developing RCs, their optimization still largely relies on heuristics and trial-and-error. Meanwhile, the emergence of mixed oxides has expanded the design space for RCs 28,[57][58][59] thus making it impractical to screen out the promising RCs given the infinitely many possible compositions of mixed oxides. Therefore, effective computational tools are highly desirable to narrow down the design space for RC development and optimization.…”

Supported Cu/W/Mo/Ni—Liquid Metal Catalyst with Core-Shell Structure for Photocatalytic Degradation

“…They are usually low-melting-point alloys (−19 • C) and have high flexibility, variable shape, high electrical conductivity, high thermal conductivity, liquidity, high surface tension and flexibility, nontoxicity, and other characteristics [4]. Liquid metal photocatalysis was based on non-toxic gallium-based alloys [5,6]. Catalysts prepared by liquid metals and their compounds have great potential for starting, accelerating chemical reactions, and improving product yield [7,8].…”