Transient resonance Raman spectroscopy for mechanistic elucidation of the CO2-assisted propane dehydrogenation

为了减轻全球变暖的影响，将产生的CO2永久地整合到闭合的CO2循环中是非常紧迫的。CO2还原与丙烷脱氢耦合生产丙烯具有巨大的技术应用潜力，因为CO2降低了产物的过氧化，将反应转移到产物侧，并转化为目前通过化石甲烷重整生产的中心平台化学品CO。负载型氧化钒催化剂是CO2辅助丙烷氧化脱氢反应中最具活性的催化剂之一，但对其操作模式（结构-活性关系）的深刻理解仍然缺失，并阻碍了商业化过程的进一步发展。该研究项目的目的是进一步开发在第一个资助期内建立的光谱方法及其在工作条件下的应用，以便从根本上了解负载型氧化钒催化剂在CO2辅助氧化丙烷脱氢中的功能。在这种情况下，除了丙烷直接还原CO2外，还将研究通过丙烷脱氢和随后的逆水煤气变换反应的间接反应途径。在方法方面，重点将放在瞬态拉曼光谱（拉曼调制激发光谱，拉曼-MES）的开发和应用上，该光谱能够探测活性物质，即即使在升高的温度（550-600°C）下也积极参与反应的物质，并且该光谱将扩展为操作方法（操作拉曼-MES）。催化剂表征将得到其他方法（紫外-可见光、红外和光电子能谱、X射线衍射）的支持，这些方法探测了（准）原位/操作条件下反应对表面和本体的影响。研究建议的一个特别重点将放在工作条件下活性氧化钒结构的分析以及它们与催化性能（活性，选择性，稳定性）的相关性。结构表征不仅包括表面的动力学，而且还包括缺陷动力学，这对CO2再氧化的动力学起着至关重要的作用。在这方面，也将详细研究辅助材料的作用。在反应条件下的瞬态拉曼光谱的应用预计将提供对CO2辅助的丙烷氧化脱氢的全新的机理洞察，其需要550-600°C的高温，因此瞬态IR光谱无法获得。

To mitigate the effect of global warming it is of great urgency to integrate generated CO2 permanently within a closed CO2 loop. The coupling of CO2 reduction with propane dehydrogenation for producing propylene, one of the most important feedstocks of the chemical industry, possesses great potential for technical application, as CO2 reduces the overoxidation of the product, shifts the reaction to the product side, and is transformed into CO, a central platform chemical, which is currently produced via reforming of fossile methane. Supported vanadia catalysts are among the most active catalysts for CO2-assisted oxidative propane dehydrogenation, but a profound understanding of their mode of operation (structure-activity relationships) is still missing and hinders further developments toward a commercial process. The aim of this research project is the further development of the spectroscopic methods, which were established in the first funding period, and their application under working conditions, in order to gain fundamentally new insight into the functioning of supported vanadia catalysts in CO2-assisted oxidative propane dehydrogenation. In this context, besides the direct CO2 reduction by propane also the indirect reaction pathway via propane dehydrogenation and subsequent reverse water gas-shift reaction will be studied. Method wise the focus will be put on the development and application of transient Raman spectroscopy (Raman modulation excitation spectroscopy, Raman-MES), which enables to probe active species, that is species actively participating in the reaction, even at elevated temperatures (550-600°C), und which will be expanded into an operando method (operando Raman-MES). The catalyst characterization will be supported by other methods (UV-Vis, IR, and photoelectron spectroscopy, X-ray diffraction), which probe the influence of the reaction on the surface and bulk under (quasi) in situ/operando conditions. A particular focus of the research proposal will be put on the analysis of active vanadia structures under working conditions as well as their correlation with the catalytic properties (activity, selectivity, stability). The structural characterization includes not only the dynamics of the surface, but also the defect dynamics, which plays an essential role for the kinetics of the re-oxidation by CO2. In this context, also the role of the support material will be studied in detail. The application of transient Raman spectroscopy under reaction conditions is expected to provide fundamentally new mechanistic insight into the CO2-assisted oxidative propane dehydrogenation, which requires elevated temperatures of 550-600°C and is therefore not accessible with transient IR spectroscopy.