铁碳化物,特别是χ-Fe5C2，因在多个不同领域的应用长期以来受到研究者的密切关注。事实上，χ-Fe5C2已经被认定为铁基费托合成催化剂的活性相。除了作为催化剂外，χ-Fe5C2在电化学、磁成像和治疗等方面也有应用价值。自发现以来，人们对χ-Fe5C2的结构、稳定性、催化性能等物理化学性质开展了研究。χ-Fe5C2的C2/c结构在上世纪60年代初次得到解析，但是受限于样品中常常混合其他氧化铁和碳化铁，在结构方面还存在争议。研究者仍致力于结合先进表征技术和理论方法，利用高纯度的样品来建立更加准确的模型。作为一种亚稳态结构，传统合成方法很难制备高纯度的χ-Fe5C2。经过对合成方法的不断探索，物相单一和尺寸形貌可控的合成已经实现。多种铁和碳的前驱体可以用来合成χ-Fe5C2，而固-固、固-气和固-液相的碳化过程均能够用来制备不同粒度和形貌的χ-Fe5C2。合成方法方面的成果来了对χ-Fe5C2物相形成机理的新认识。利用原位表征方法，研究者已经揭示了气固相和液固相制备过程中物相形成的一些细节。无定形的Fe-C复合物的形成与晶化有可能是关键步骤。在新的制备方法基础上，出现了多种调控χ-Fe5C2催化活性的新手段。低钴含量的有钴纳米粒子和χ-Fe5C2组成的复合体具有非常高的低温费托合成活性。通过第二组分的修饰后可以使χ-Fe5C2突破传统的费托合成反应的局限，成为制备低碳烯烃、长链α烯烃、芳烃和含氧化物的新型催化剂。在这篇综述中，我们将回顾自上世纪中期以来对χ-Fe5C2物相的研究成果，聚焦于对结构解析，制备方法，生成机制以及在催化性能调控等方面的进展。我们总结了一系列用于制备χ-Fe5C2的方法以及控制催化性质的路径。合成方法的突破是更好认识χ-Fe5C2物理化学的关键。
Iron carbides, especially H？gg carbide (χ-Fe5C2), have become a topic of significant research interest due to their potential application in various fields over the past decades. For Fischer-Tr？ psch (F-T) synthesis, χ-Fe5C2 has been confirmed as an active phase. In addition, this well-known catalytic material is a candidate for potential application in electrochemistry, magnetic imaging, and various therapies. The physical chemistry, including structure, stability, and catalytic properties of χ-Fe5C2 has been studied since its discovery. The C2/c crystal structure of H？gg carbide was initially resolved in the 1960s. Because various iron oxides and carbides always co-exist in the synthesized χ-Fe5C2 samples, the structure model still faces challenges. The crystal structure is being revised with high-purity samples using modern characterization techniques and theoretical methods. However, it is very difficult to obtain the pure phase of χ-Fe5C2 via traditional preparation methods owing to the metastable phase of χ-Fe5C2. Hence, tremendous efforts have been devoted to the synthesis of χ-Fe5C2. Recently, some processes to prepare single-phase and structure-controlled χ-Fe5C2 nanostructures have been reported. Many iron and carbon precursors can be used to prepare H？gg carbide. Carburization in solid-solid, solid-gas, and solid-liquid phases can be adopted to synthesize χ-Fe5C2 of various sizes and morphologies. The success of synthetic chemistry has provided novel insights into the mechanism of phase transformation in χ-Fe5C2. More details regarding the formation of the χ-Fe5C2 structure in the solid-gas and solid-liquid phases have been revealed via in situ characterization methods. The formation and crystallization of an Fe-C amorphous composite is likely the key step. The application of χ-Fe5C2 in catalysis has also