物理化学学报 >> 2020, Vol. 36 >> Issue (1): 1906087.doi: 10.3866/PKU.WHXB201906087

所属专题: 庆祝唐有祺院士百岁华诞特刊

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χ-Fe5C2:结构,合成与催化性质调控

赵华博1,马丁2,*()   

  1. 1 北京低碳清洁能源研究院,北京 102211
    2 北京大学化学与分子工程学院,北京 100871
  • 收稿日期:2019-06-27 录用日期:2019-08-19 发布日期:2019-08-22
  • 通讯作者: 马丁 E-mail:dma@pku.edu.cn
  • 作者简介:马丁教授,2001年在中国科学院大连化学物理研究所取得博士学位,2009年加入北京大学化学与分子工程学院物理学研究所,从事多相催化研究,着力于发展新的催化体系,结合原位表征手段来解决催化过程中的重要科学问题
  • 基金资助:
    国家重大专项项目(2017YFB0602500)

χ-Fe5C2: Structure, Synthesis, and Tuning of Catalytic Properties

Huabo Zhao1,Ding Ma2,*()   

  1. 1 National institute of Low Carbon and Clean Energy, Beijing 102211, P. R. China
    2 College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2019-06-27 Accepted:2019-08-19 Published:2019-08-22
  • Contact: Ding Ma E-mail:dma@pku.edu.cn
  • Supported by:
    the National Key Research and Development Program of China(2017YFB0602500)

摘要:

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-Fe5C2C2/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。

关键词: χ-Fe5C2, 费托合成, 材料合成, 原位表征, 助剂

Abstract:

Iron carbides, especially Hägg 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-Trö 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 Hägg 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 Hägg 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 benefited from novel synthesis strategies. With the development of these preparation methods, tuning the activity and selectivity of χ-Fe5C2 has become possible. A heterostructure of small Co/χ-Fe5C2 with low cobalt loading showed an unexpectedly high CO conversion rate at low temperature. Beyond classical F-T synthesis, χ-Fe5C2 is a promising catalyst for the production of light olefins, long chain α-olefins, aromatics, and alcohol synthesis by modification with other elements. Combining density functional theory (DFT) calculations and kinetic analysis, the roles of promoters and interaction with χ-Fe5C2 have been evaluated to some extent. Herein, the recent progress in the synthesis, structural analysis, formation mechanisms, and catalytic performance of χ-Fe5C2 is summarized. A collection of synthesis methods is presented, and novel methods for regulating catalytic properties are reviewed. We believe that advanced synthesis methods are key to a deeper understanding and better utilization of this material.

Key words: χ-Fe5C2, Fischer Tröpsch synthesis, Materials synthesis, In situ characterization, Promoter

MSC2000: 

  • O643.3