Spatially resolved operando characterization of catalytically active species and sites during CO2 activation

• Applicant: Professor Dr. Christian Hess
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561060456

In the context of global warming, the global challenge is to reduce the amount of atmospheric CO2. Among other measures, the catalytic conversion of CO2 into valuable products (e.g. methanol) in particular represents a sustainable approach to reduce CO2 emissions and the dependence on fossil fuels. For the knowledge-based development of improved catalysts, the analysis of the catalyst structure and in particular the active sites under reaction conditions is of central importance. It is known that gradients are formed in catalytic reactors due to the changing chemical potential, which modify the catalyst properties. For a comprehensive understanding of the functioning of catalysts for CO2 conversion, also with regard to possible process control, the development of spatially resolved methods is therefore necessary to identify the catalytically active species and centers along the catalyst bed. The aim of the planned research project is to obtain spatially-resolved insights into the nature of the active species and sites of AuZnCe and CuZnCe catalysts in the reverse water gas shift reaction by means of a profile reactor and by using optical spectroscopy under working conditions. Modulation-excitation spectroscopy (MES), which was recently developed in the research group, is used to identify the catalytically active species and sites, which allows the recording of transient Raman and UV-Vis spectra, while MES-IR spectroscopy is applied under isopotential conditions. In addition, the extension of transient Raman spectroscopy to surface-enhanced spectroscopy (SERS) will be explored, which can significantly increase the sensitivity and surface specificity of Raman analysis. Catalyst characterization is supported by other in situ/operando methods such as X-ray diffraction, impedance and X-ray photoelectron spectroscopy as well as electron microscopy methods. The research project aims in particular at the spatially-resolved analysis of the active catalyst sites and active adsorbate species and their correlation with the catalytic properties (activity, selectivity, stability) during the reverse water gas shift reaction. In this context, the interplay of surface and volume chemistry (UV-Vis, IR, SERS) including defect dynamics (Raman) will also be addressed, and the extent to which the behavior changes depending on the reactor position and temperature will be clarified. By varying the metal (Au, Cu), metal-specific influences on catalysis, such as alloy formation, metal-carrier interactions and electronic effects, will be investigated in more detail.

• DFG Programme: Research Grants
• Major Instrumentation: Profilreaktor mit Spektroskopiezugang
• Instrumentation Group: 1110 Reaktionsgefäße für Niederdruck, (Hydrierung, Katalyse, Polymerisation)