Mechanistic insight into pressure-dependent CO2 hydrogenation over indium oxide catalysts using new operando methods and transient spectroscopy

应对全球变暖并将产生的二氧化碳纳入一个封闭的二氧化碳循环，从而显著减少或理想地防止额外的二氧化碳排放到大气中，这是最紧迫的。除其他手段外，特别是利用再生生产的H2催化将CO2转化为甲醇是减少CO2排放和对化石能源载体依赖的可持续途径，并进一步开辟了长期储存可再生能源电力的可能性。铟氧化物已成为CO2活化的有前途的催化剂，但在技术上相关的CO2加氢中，对其操作模式（结构-活性关系）的基本理解仍然缺失，阻碍了催化过程的进一步发展。该项目的目的是通过在工作条件下使用光学和阻抗光谱，对氧化铟催化剂用于二氧化碳加氢的操作模式获得基本的新见解。在此背景下，除了常压下的逆水气变换反应（rWGSR）外，还将研究CO2加氢的压力依赖性及其对甲醇形成的影响。此外，我们将探讨贵金属（Au, Cu）对催化性能的作用。在方法上，重点是开发和应用合适的操作方法（红外，拉曼，紫外-可见，阻抗光谱）以及瞬态红外光谱的应用，所有这些方法都可以在高压（~30 bar）下应用。氧化铟催化剂的表征将得到其他方法的支持，如原位x射线衍射和原位x射线光电子能谱以及DFT计算。除了系统的开发外，项目的重点是分析工作条件下氧化铟的结构及其与催化性能（活性、选择性、稳定性）的相关性。特别感兴趣的是表面化学的阐明，包括缺陷动力学，这在很大程度上是未知的，以及它对温度和压力的依赖。在这种情况下，我们将一方面使用（瞬态）红外光谱，因为它具有固有的特异性，另一方面使用拉曼光谱，紫外-可见光谱和阻抗光谱，因为它们对缺陷的敏感性，从它们的结合中可以期望对氧化铟催化剂的基本新机制的了解。

It is of the outmost urgency to counteract to global warming and to include produced CO2 into a closed CO2 cycle, thereby significantly reducing or ideally preventing the emission of additional CO2 into the atmosphere. Besides other means, in particular, the catalytic transformation of CO2 into methanol using regeneratively produced H2 is a sustainable approach for reducing CO2 emissions and the dependence on fossil energy carriers, and furthermore opens up the possibility of long-term storage of electricity from renewable energy sources. Indium oxides have emerged as promising catalysts for CO2 activation, but a fundamental understanding of their mode of operation (structure-activity relations) in the technically relevant CO2 hydrogenation is still missing and hampers the further development of the catalytic processes. The aim of this project is to gain fundamental new insight into the mode of operation of indium oxide catalysts for CO2 hydrogenation, by employing optical and impedance spectroscopy under working conditions. In this context, beside the reverse water-gas shift reaction (rWGSR) at atmospheric pressure, also the pressure dependence of the CO2 hydrogenation and its influence on methanol formation will investigated. In addition, we will explore the role of noble metals (Au, Cu) on the catalytic properties. Methodically, the focus is on the development and application of suitable operando methods (IR, Raman, UV-Vis, impedance spectroscopy) as well as the application of transient IR spectroscopy, all of which can be applied at elevated pressures (~30 bar). The characterization of the indium oxide catalysts will be supported by additional methods such as in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy as well as DFT calculations. Beside the methodical development a focus of the project is on the analysis of the indium oxide structure(s) under working conditions as well as their correlation with the catalytic properties (activity, selectivity, stability). Of particular interest is the elucidation of the surface chemistry including the defect dynamics, which is largely unexplored, and its dependence on temperature and pressure. In this context, we will on one hand employ (transient) IR spectroscopy because of its intrinsic specificy, and on the other hand Raman, UV-Vis and impedance spectroscopies due their sensitivity towards defects, from the combination of which fundamental new mechanistic insight into indium oxide catalysts can be expected.