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

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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.