Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer-Tropsch Catalysts
Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer-Tropsch Catalysts
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DOI：
10.1021/acscatal.7b04085
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发表时间：
2018-04-01
期刊：
影响因子：
12.9
通讯作者：
Li, Yongwang
中科院分区：
文献类型：
--
作者：
Chang, Qiang;Zhang, Chenghua;Li, Yongwang
研究了不同种类的碳化铁对铁基费托催化剂活性和选择性的影响。通过将二元Fe/SiO2模型催化剂（通过共沉淀法制备）预处理至不同的气体气氛（合成气、CO或H-2）来获得不同的碳化铁相。采用XRD、XAFS、MES和TEM等手段对催化剂的相结构、组成和粒径进行了系统表征。发现在经合成气处理的催化剂中，仅形成xi-Fe_5C_2碳化物。在CO处理的催化剂中，形成具有双峰粒度分布的Fe 7 C3和chi-Fe 5C 2，而H2处理的催化剂在费托合成（FTS）反应之后表现出双峰粒度分布的ε-Fe 2C和chi-Fe 5C 2。计算固有FTS活性，并基于相组成和粒度分配给每个相应的碳化铁。经鉴定，在典型的中温费托（MTFT）条件（260-300摄氏度，2-3 MPa，和H-2/CO = 2）下，在三种候选碳化物（ε-Fe 2C、Fe 7 C3和chi-Fe 5C 2）中，Fe 7 C3具有最高的本征活性（TOF = 4.59 × 10（-2）s（-1））。此外，在ε-Fe 2C上的FTS导致最低的甲烷选择性。
The influence of different iron carbides on the activity and selectivity of iron-based Fischer-Tropsch catalysts has been studied. Different iron carbide phases are obtained by the pretreatment of a binary Fe/SiO2 model catalyst (prepared by coprecipitation method) to different gas atmospheres (syngas, CO, or H-2). The phase structures, compositions, and particle sizes of the catalysts are characterized systematically by XRD, XAFS, MES, and TEM. It is found that in the syngas-treated catalyst only chi-Fe5C2 carbide is formed. In the CO-treated catalyst, Fe7C3 and chi-Fe5C2 with a bimodal particle size distribution are formed, while the H2-treated catalyst exhibits the bimodal size distributed epsilon-Fe2C and chi-Fe5C2 after a Fischer-Tropsch synthesis (FTS) reaction. The intrinsic FTS activity is calculated and assigned to each corresponding iron carbide based on the phase composition and the particle size. It is identified that Fe7C3 has the highest intrinsic activity (TOF = 4.59 x 10(-2) s(-1)) among the three candidate carbides (epsilon-Fe2C, Fe7C3, and chi-Fe5C2) in typical medium-temperature Fischer-Tropsch (MTFT) conditions (260-300 degrees C, 2-3 MPa, and H-2/CO = 2). Moreover, FTS over epsilon-Fe2C leads to the lowest methane selectivity.