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_0.6Sr_0.4Fe_0.8Al_0.2O_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 Fe⁰@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 H₂O–CO₂ 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 H₂/CO ratio of 2/1.

Iron-based oxides are promising oxygen carriers for thermochemical syngas production, but can be prone to deactivation during the reaction. Here an iron-based catalyst is shown to transform reversibly between perovskite and core–shell structures during methane-to-syngas conversion, accounting for its high stability toward coke deposition.