x-Fe5C2与θ-Fe3C在逆水煤气变换中的结构演变规律OA

Iron-based catalysts often undergo dynamic carburization and oxidation phase transitions in a CO2/H2 atmosphere.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 x-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 ℃),pulse experiments(270 ℃)and in situ XRD(10％CO2/He,340 ℃),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 x-Fe5C2 exhibits higher RWGS activity but is more susceptible to oxidation during the reaction.In contrast,θ-Fe3C demonstrates stronger anti-oxidation stability but lower RWGS activity.Under RWGS conditions with H2,θ-Fe3C can partially transform into x-Fe5C2.However,in 10％CO2 atmosphere,both carbides are directly oxidized to Fe3O4,with no observed phase transformation between the iron carbides.These findings reveal the differences in the evolution mechanisms of x-Fe5C2 and θ-Fe3C under different atmospheres,providing experimental basis for the regulation of phase structure and optimization of operational stability in iron-based Fischer-Tropsch and RWGS catalysts.