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Chinese Journal of Catalysis 34 (2013) 1312–1325 催化学报 2013年 第34卷 第7期 | available at journal homepage: Article Controlling the phase transformations and performance of iron‐based catalysts in the Fischer‐Tropsch synthesis GAO Fangfang a,b, WANG Hong c, QING Ming c, YANG Yong a,c,*, LI Yongwang a,c a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China b University of Chinese Academy of Sciences, Beijing 100049, China c Synfuels China Co. Ltd, Beijing 101407, China ARTICLE INFO ABSTRACT Article history: Received 25 January 2013 Accepted 27 February 2013 Published 20 July 2013 The phase transformations of a series of iron‐based models of the catalysts used in the Fisch‐er‐Tropsch synthesis (FTS) were controlled using a combination of deep reduction followed bypartial carburization. The catalysts were pretreated under a variety of different conditions and their performance in the FTS subsequently tested in a fixed‐bed reactor. The physiochemical properties of the catalysts were characterized by X‐ray diffraction (XRD), Mössbauer effect spectroscopy (MES), H2 temperature‐programmed desorption (TPD), and laser Raman spectroscopy (LRS) before and after the reaction. The results indicated that the catalysts consisted predominately of α‐Fe par‐ticles following the H2 reduction. The size of the crystals and the stability of the catalysts increased with increasing reduction temperature. The carburization process mainly occurred on the surface of the α‐Fe particles, and the rate of the carburization process could be effectively controlled usingC2H4. Compared with the catalysts activated with H2 or syngas, the catalysts initially activated with H2 followed by C2H4 exhibited better performance in the FTS. © 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.Published by Elsevier B.V. All rights reserved.Keywords: Fischer‐Tropsch synthesis Iron‐based catalyst Phase control Reduction temperature Reduction atmosphere 1. Introduction The Fischer‐Tropsch synthesis (FTS) is a process for con‐verting syngas derived from coal, nature gas, biomass and oth‐er carbon‐containing resources to hydrocarbons and other useful chemicals [1]. The development of effective catalysts and relevant industrial technologies are the two key areas of re‐search concerning the development of the FTS. Fe and Co are two of the most promising catalyst systems for the industrial application of the FTS [2,3]. In recent years, Fe‐based catalysts have become the subject of increasing levels of attention be‐cause of their high activity towards the FTS, moderate activity towards the water gas shift (WGS) reaction, lower price and flexible operating conditions [4,5]. Fresh iron‐based catalysts consist predominantly of Fe2O3. Fe2O3 cannot catalyze the FTS reaction, and the iron‐based cat‐alysts must therefore be activated prior to their use in the FTS reaction to form an active phase, with FexC generally being reported to be the stable active phase [1–8]. Iron‐based cata‐lysts are typically pretreated with H2, CO or syngas [9]. Fe2O3 is reduced to Fe3O4 and ‐Fe when it is pretreated with H2. These Fe3O4 and α‐Fe particles would be readily carburized under the reaction conditions to form iron carbide. Furthermore, the oxi‐dation reactions of ‐Fe and FexC, as well as carbon deposition, could not be simultaneously excluded from this reaction. Con‐sequently, catalysts reduced with H2 generally exhibit a loose * Corresponding author. Tel: +86‐10‐69667699; Fax: +86‐10‐69667653; E‐mail: yyong@sxicc.ac.cn This work was supported by the National Natural Science Foundation of China (20703054), the National Basic Research Program of China (973 Pro‐gram, 2011CB201401), and the National High Technology Research and Development Program of China (863 Program, 2011AA05A205). DOI: 10.1016/S1872‐2067(12)60562‐2 | | Chin. J. Catal., Vol. 34, No. 7, July 2013 GAO Fangfang et al. / Chinese Journal of Catalysis 34 (2013) 1312–1325 1313 structure and poor mechanical strength. Furthermore, although they usually have a higher initial activity, they have a high de‐activation rate. When iron‐based catalysts are activated with CO, the Fe2O3 particles are converted to Fe3O4 and FexC. Unfor‐tunately, however, the process is also accompanied by severe carbon deposition [10], which has an adverse impact on the activity of catalysts. If the iron‐based catalysts could be acti‐vated with syngas, then the Fe2O3 would be converted to Fe3O4 and FexC [11–15]. One of the key benefits of using syngas is the suppression of carbon deposition, which results from the presence of H2. It is inevitable, however, that the FTS reaction would also take place during the pretreatment of the catalysts with syngas. The active phase formed on the surface of the cat‐alyst during the