Structure and kinetics of iron-catalysts in the initial phase of the Fischer-Tropsch synthesis: Combination of Operando-XRD and studies in a fixed-bed reactor

费托合成初始阶段铁催化剂的结构和动力学：操作 XRD 与固定床反应器研究的结合

• 批准号: 412867760
• 负责人: Professor Dr.-Ing. Andreas Jess
• 金额: --
• 依托单位: Lehrstuhl für Chemische Verfahrenstechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/412867760?language=en
• 关键词: Structure; kinetics; iron; catalysts; initial

In the Fischer-Tropsch synthesis (FTS) CO an H2 are converted to higher hydrocarbons (and water as by-product). Catalysts employed are usually on the basis of cobalt or iron. Especially in the case of iron based catalysts it is not clear until today, which phase(s) catalyse the FT-reaction. The main reason for this is that the actual catalyst is only formed under synthesis conditions during the initial phase of the FTS and the solid phases in the catalyst form a complex mixture of metalic iron, iron oxides and -carbides. Even though the composition of iron catalysts has been studied ex situ via X-ray diffraction (XRD), Moessbauer- and X-ray photoelectron spectroscopy in the past, only very few studies combine the composition and the dependency of the catalytic behaviour thereof. It is well-known that iron catalysts are activated during the initial stage of the FT-reaction. Along with this activation Fe-carbides are formed, from which it was concluded that these carbides are active for the FTS. Nevertheless, this conclusion and, additionally, which carbide phase is the (more/most) active one, is still disputed"Accordingly, the information on the phase structure of the "working" catalyst can hardly be gained, even with a very detailed characterisation of the fresh catalyst. It is also doubtful if the ex situ characterisation of used or spent catalysts, which typically is done in inert atmosphere and at room temperature, supplies definite information on the structure of the catalyst under process conditions. Our preliminary studies with in operando XRD and kinetic measurements in a fixed bed reactor show, that the formation of Fe-phases in the catalyst depends on the reductive pretreatment, the composition (promoters) of the (fresh) catalyst and on the conditions during actual FTSIn the proposed project the formation of different Fe-phases shall be studied by in operando XRD, i.e. at FT-reaction conditions,he focus is thereby the so-called low temperatur FTS (T < 250°C) until steady state is reached. It shall also be examined, how the formation of different Fe-phases depends on pretreatment, promoters and reaction conditions (temperature, pressure, partial pressures of CO, H2 and water vapour). Complementarily, the activity and selectivity of the catalysts will be examined in a fixed bed reactor under the same reaction conditions. Thus, information on the structure-response-relationship ("phases of catalyst and kinetics") shall be gained and the phase(s), which is/are active in FTS, should be identified. It is also of great interest, whether the activity and selectivity finally reached in steady state can be adjusted a priori by a proper choice of promoters and/or reductive pretreatment.

在费托合成 (FTS) 中，CO 和 H2 被转化为高级烃（以及副产物水），所使用的催化剂通常基于钴或铁，尤其是在铁基催化剂的情况下。直到今天，哪个相催化费托反应的主要原因是实际的催化剂仅在费托合成的初始阶段的合成条件下形成，并且催化剂中的固相形成。金属铁、铁氧化物和碳化物的复杂混合物尽管过去已经通过 X 射线衍射 (XRD)、穆斯堡尔和 X 射线光电子能谱对铁催化剂的组成进行了非原位研究，但只有很少的研究将其结合起来。众所周知，铁催化剂在FT反应的初始阶段被活化，并形成铁碳化物。结论是这些碳化物对于 FTS 是活跃的，然而，这一结论以及哪种碳化物相是（更多/最）活跃的碳化物相仍然存在争议。“因此，有关“工作”相结构的信息。即使对新鲜催化剂进行了非常详细的表征，也很难获得催化剂。通常在惰性气氛和室温下进行的用过或废催化剂的异位表征是否提供了有关结构的明确信息也是值得怀疑的。正在处理的催化剂我们在固定床反应器中进行的现场 XRD 和动力学测量的初步研究表明，催化剂中 Fe 相的形成取决于还原预处理、（新鲜）催化剂的组成（促进剂）和条件。在实际 FTS 期间，在所提出的项目中，应通过操作 XRD 研究不同 Fe 相的形成，即在 FT 反应条件下，因此重点是所谓的低温 FTS（T < 250°C），直到达到稳定状态，还应检查不同铁相的形成如何取决于预处理、促进剂和反应条件（温度、压力、CO、H2 和水蒸气的分压）。催化剂的活性和选择性将在相同的反应条件下在固定床反应器中进行检查，因此，应获得有关结构-响应关系（“催化剂的相和动力学”）的信息。应该确定在 FTS 中具有活性的获得的相和相。同样重要的是，最终达到稳态的活性和选择性是否可以通过适当选择调整启动子和/或来预先确定。或还原预处理。