Heterogeneous iron catalysts are active in the hydrogenation of carbon oxides and are widely investigated for the production of long‐chained hydrocarbons according to the Fischer‐Tropsch synthesis. Moreover, high selectivity of light hydrocarbons, such as CH4, also occurs strongly depending on reaction conditions and catalyst formulations. As a consequence, Fe catalysts reveal promising methanation activity as referred to the traditional Ni catalysts. Additionally, Fe catalysts also benefit from their low price and toxicological harmlessness. However, the dynamic behavior of iron upon CO2 hydrogenation is not yet unraveled unambiguously including phase transformations, structural changes and participation of carbon species formed. The present review highlights these complex processes of Fe catalysts with special focus on the methanation of CO2. Additionally, different analytical tools useful for ex situ and in situ studies are critically evaluated.

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Fe@SiO2 core–shell model catalysts were investigated for the conversion of CO2 and H2 into CH4, CO and H2O. For evaluation of the effect of core size on the catalytic activity, samples with Fe particle sizes of 4, 6 and 8 nm were prepared. Fresh and spent catalysts were thoroughly characterized by X-ray diffraction, 57Fe Mössbauer spectroscopy, transmission electron microscopy, temperature programmed hydrogenation and X-ray photoelectron spectroscopy. As a result, the yield of the major product CO as well as CH4 was increased with Fe core size. Additionally, growing Fe cores led to stronger carburization and higher amount of reactive carbide entities, which drive the CH4 formation. Finally, formation of inactive bulk carbon deposition is strongly suppressed for the core–shell catalysts in comparison to bulk iron oxide catalysts used for CO2 hydrogenation.

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