In situ encapsulation of iron(0) for solar thermochemical syngas production over iron-based perovskite material

Abstract

Methane-to-syngas conversion plays an important role in industrial gas-to-liquid technologies, which is commercially fulfilled by energy-intensive reforming methods. Here we present a highly selective and durable iron-based La 0.6 Sr 0.4 Fe 0.8 Al 0.2 O 3-δ oxygen carrier for syngas production via a solar-driven thermochemical process. It is found that a dynamic structural transformation between the perovskite phase and a Fe 0 @oxides core-shell composite occurs during redox cycling. The oxide shell, acting like a micro-membrane, avoids direct contact between methane and fresh iron(0), and prevents coke deposition. This core-shell intermediate is regenerated to the original perovskite structure either in oxygen or more importantly in H 2 O-CO 2 oxidant with simultaneous generation of another source of syngas. Doping with aluminium cations reduces the surface oxygen species, avoiding overoxidation of methane by decreasing oxygen vacancies in perovskite matrix. As a result, this material exhibits high stability with carbon monoxide selectivity above 95% and yielding an ideal syngas of H 2 /CO ratio of 2/1.

Chemical looping beyond combustion – a perspective

“…These unique properties make mixed oxides an intriguing option for CLBC, as illustrated by a number of recent publications. 61,70,135 Among the various mixed oxides, perovskite-type oxides represent a large family of materials that is particularly promising for CLBC due to their highly tunable structural, compositional, and redox properties. [136][137][138] A recent perspective provided a comprehensive discussion on perovskites as redox catalysts for CLBC.…”

Efficient CO2 to CO conversion at moderate temperatures enabled by the cobalt and copper co-doped ferrite oxygen carrier

“…The selection of a high-performance oxygen carrier [17 , 18] capable of being reduced and oxidized over multiple cycles without significant deactivation is a crucial consideration for the development of chemical looping CO 2 splitting processes. Iron oxides have been recognized as the most applicable OCMs and attracting many focuses owing to its low-cost and environmental compatibility [19] . However, pure iron oxides for chemical looping application requires harsh operating conditions ( > 800 °C) to insure the sufficient CO 2 splitting rate and total CO yield [20] .…”

Recent Advances of Oxygen Carriers for Chemical Looping Reforming of Methane

“…Huang et al. reported a Sr and Al substitution for La and Fe in La 0.6 Sr 0.4 Fe 0.8 Al 0.2 O 3‐δ perovskite OC not only reduced surface active oxygen species for CH 4 over‐oxidation but also facilitated in situ encapsulation of Fe 0 , originating from deep reduction of Fe 4+ with the formation of Fe 0 @oxides composite, as presented in Figure 11(a–c) [47h] . With the structure engineering process, total oxidation was suppressed and CH 4 pyrolysis on Fe 0 was switched off.…”

“… (a) XPS results of O1s peak and (b) Room temperature 57 Fe Mössbauer spectra of LaFeO 3 , La 0.6 Sr 0.4 FeO 3‐δ (LSF6410), and La 0.6 Sr 0.4 Fe 0.8 Al 0.2 O 3‐δ (LSAF6428) catalysts; (c) Proposed structural evolution over LSAF6428 for the selective oxidation of methane to syngas. White boxes represent the coordination unsaturated Fe cations; (d) CH 4 conversion, CO selectivity, and H 2 /CO ratio in the selective oxidation CH 4 step and (e) Corresponding H 2 O, CO 2 conversion, and H 2 /CO ratio in reoxidation step [47h] . Reproduced with permission from Ref.…”