Structural Evolution Regulation of χ-Fe5C2 and θ-Fe3C in the Reverse Wa-ter-Gas Shift Reaction

The identification of the active phase and the control of stability remain key challenges affecting their industrial application. This study employed a gas-solid carburization method to prepare high-purity single-phase χ‑Fe5C2 (Hägg carbide) and θ‑Fe3C (cementite), with their structural purity systematically confirmed by XRD and Mössbauer spectroscopy (MES).

Using techniques including fixed-bed reactor tests (H2/CO2=1, 0.1 MPa, 270–420 °C), pulse experiments (270 °C), and in-situ XRD (10% CO2/He, 340 °C), the catalytic performance and structural evolution pathways of these carbides in the reverse water-gas shift (RWGS) reaction were thoroughly investigated. The results indicate that χ‑Fe5C2 exhibits higher RWGS activity but is more susceptible to oxidation during the reaction.