Unravelling magnetite structural dynamics and deactivation pathways during CO₂ hydrogenation

The rational design of heterogeneous catalysts is crucial for identifying structure–performance relationships and understanding the nature of active site alteration during catalyst life cycles. In this study, the hydrogenation of CO₂ to generate hydrocarbons was performed over a magnetite (Fe₃O₄)-based catalyst, and the structural evolution of the catalyst during long-term stability testing was comprehensively studied. The transformation of the α-Fe phase into Fe₃O₄ and χ-Fe₅C₂ phases after 100 h of reaction, followed by a decline in Fischer–Tropsch synthesis activity after 500 h, was attributed to the blockage of the χ-Fe₅C₂ phase by carbon deposition. Although oxidation of χ-Fe₅C₂ is an unavoidable process, the presence of a significant χ-Fe₅C₂ content after 500 h of reaction indicated that carbon deposition occurs, blocking the active sites and deactivating the catalyst. This behavior was clearly observed using temperature-programmed oxidation and Mössbauer spectroscopy, indicating that the deactivation and structural evolution of catalysts are strongly related during the CO₂ hydrogenation reaction.