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 H₂). 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 χ-Fe₅C₂ carbide is formed. In the CO-treated catalyst, Fe₇C₃ and χ-Fe₅C₂ with a bimodal particle size distribution are formed, while the H₂-treated catalyst exhibits the bimodal size distributed ε-Fe₂C and χ-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 × 10^–2 s^–1) among the three candidate carbides (ε-Fe₂C, Fe₇C₃, and χ-Fe₅C₂) in typical medium-temperature Fischer–Tropsch (MTFT) conditions (260–300 °C, 2–3 MPa, and H₂/CO = 2). Moreover, FTS over ε-Fe₂C leads to the lowest methane selectivity.

中文翻译：

---

铁碳化物相（ε -铁之间关系₂ C，铁₇ Ç ₃，和χ -铁₅ Ç ₂）和铁/二氧化硅的催化性能₂的费-托催化剂

研究了不同碳化铁对铁基费-托催化剂活性和选择性的影响。通过将二元Fe / SiO ₂模型催化剂（通过共沉淀法制备）预处理到不同的气体气氛（合成气，CO或H ₂）中，可以得到不同的碳化铁相。催化剂的相结构，组成和粒度通过XRD，XAFS，MES和TEM进行系统表征。据发现，在合成气处理的催化剂仅χ -铁₅ c ^ ₂形成碳化物。在铁的CO-处理过的催化剂，₇ Ç ₃和χ -铁₅ Ç ₂具有双峰粒度分布形成的，而H ₂ -处理的催化剂显示出分布ε -铁的双峰粒度₂ C和χ -铁₅ c ^ ₂的费-托合成（FTS）反应后。根据相组成和粒径计算固有的FTS活性并将其分配给每个相应的碳化铁。识别出的Fe ₇ C ^ ₃具有最高的固有活性（TOF = 4.59×10 ^-2小号^-1）三个候选碳化物（ε -铁中₂ C，铁₇ Ç ₃，和χ -铁₅ Ç ₂）在典型的中等温度费托（MTFT）条件下（260–300°C，2-3 MPa，H ₂ / CO = 2）。此外，FTS过ε -铁₂下通到最低甲烷选择性。