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转化为高级烃（和水作为副产物）。使用的催化剂通常基于钴或铁。特别是在铁基催化剂的情况下，直到今天还不清楚哪个相催化FT反应。其主要原因是实际的催化剂仅在FTS的初始阶段期间在合成条件下形成，并且催化剂中的固相形成金属铁、铁氧化物和铁碳化物的复杂混合物。尽管铁催化剂的组成在过去已经通过X射线衍射（XRD）、穆斯堡尔谱和X射线光电子能谱进行了非原位研究，但是只有非常少的研究将组成和其催化行为的依赖性结合起来。众所周知，铁催化剂在FT反应的初始阶段被活化。沿着该活化形成Fe-碳化物，由此得出结论，这些碳化物对于FTS是活性的。然而，这一结论，以及另外，哪个碳化物相是（更/最）活性的，仍然是有争议的。因此，即使对新鲜催化剂进行非常详细的表征，也很难获得关于“工作”催化剂的相结构的信息。用过或废催化剂的非原位表征（通常在惰性气氛和室温下进行）是否提供了工艺条件下催化剂结构的明确信息也是值得怀疑的。我们在固定床反应器中进行的初步研究表明，催化剂中Fe相的形成取决于还原预处理，组成，（新鲜）催化剂的（促进剂）和实际FT S期间的条件。在拟定项目中，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，焦点是所谓的低温FTS（T < 250°C），直到达到稳定状态。还应检查不同Fe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）。另外，在相同的反应条件下，在固定床反应器中考察催化剂的活性和选择性。因此，应获得关于结构-响应-关系的信息（“催化剂和动力学的阶段”），并应确定在FTS中具有活性的阶段。同样令人感兴趣的是，在稳态下最终达到的活性和选择性是否可以通过适当选择促进剂和/或还原预处理来先验地调节。