Catalysts in Focus: Spectroscopic Toolbox for Mapping Local Temperature and Reaction Phenomena

The catalytic conversion of CO2 into value-added chemical building blocks is a crucial process towards a more sustainable society. The performance of the catalysts for this conversion process can be tracked using analytical methods, including spectroscopy and microscopy, which can aid towards a better understanding and optimization of these catalyst materials. The length scales of importance for a catalytic reaction vary over multiple orders of magnitude, where each length scale provides additional physicochemical insights into the functioning of the catalyst. Consequently, spectroscopy and microscopy methods need to be applied to this variety of length scales. In this PhD Thesis, we show the development and application of two spectroscopic methods to probe the local temperature and reaction intermediates, namely luminescence thermometry and Raman spectroscopy, at a spatial resolution of 1 µm2 and temporal resolution of seconds. The results described in the different chapters provide a methodological view on the application of these analytical methods and showcase spatially resolved information on the catalytic performance. We optimized the lanthanide-based luminescent thermometer to have optimal signal strength, resulting in low temperature uncertainties. The thermometer particles were used to study the temperature change in two processes: 1) the thermocatalytic CO2 hydrogenation reaction and 2) the electrocatalytic hydrogen and oxygen evolution reactions. We found significant temperature increase upon the introduction of the reactant gasses CO2 and H2 during process 1 due to exothermic reactions at the catalyst surface, as well as temperature variations as a function of current density and electrolyte composition in process 2. Furthermore, the reaction intermediates of the CO2 hydrogenation reaction were studied with plasmonic substrates, for which we provided more robust and homogeneous alternatives based on a combination of atomic layer deposition and lithography. Further progress can be made in the combination of the two analytical methods, as well as more efficient designs of operando reactor cells. This PhD Thesis can be used as a guideline for spatiotemporal spectroscopic studies during catalytic reactions to map out local effects such as temperature and reaction intermediates.