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

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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.