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Five different iron carbide phases could be formed during Fischer-Tropsch synthesis: Hagg carbide(χ-Fe5C2),pseudo-hexagonal iron carbide(ε-Fe2C),cementite(θ-Fe3C)and Eckstr(o)m-Adcock iron carbide(Fe7C3).The catalytically active phase(s)in a working iron-based catalyst for FTS has been debated extensively by researchers.The focus of the work here was on preparing the single-phase iron carbide,which were used be model catalysts for mechanistic study of FTS.The optimal conditions of preparation of iron carbides(ε-Fe2C,χ-Fe5C2,θ-Fe3C)were obtained by adjusting the ratio of syngas.The result of In situ XRD demonstrates that ε-Fe2C is stabilized up to 310 ℃,and then transformed toχ-Fe5C2from 310 to 440 ℃; θ-Fe3C appears up to 440 ℃ whilst it is decomposed into Fe and graphite.