Advanced X-ray absorption spectroscopy Analyzing electronic structures of catalysts

In catalysis, it is important to know the exact structure of the catalyst, especially under catalytic conditions. Spectroscopic information on the catalyst is crucial to reveal for example structure-activity relationships or typical ligand effects, as this allows further rational development of catalysts. In this work, X-ray Absorption Spectroscopy (XAS) has been used for the in-situ identification of intermediate species during catalysis with the use of stopped-flow (SF) and freeze-quench (FQ) methodologies. This approach allowed for time-resolved experimentation on liquid systems down to the millisecond (ms)time resolution and shows noteworthy changes of the catalyst structure during the catalytic process. XAS is a very powerful technique to determine the local structure around the absorber atom: type and number of neighboring atoms, their respective bond distances, together with electronic properties. In more detail, we developed and used various XAS methods to study different catalytic processes. Highlights include XAS in combination with fast data acquisition, identifying reactive intermediate species, in combination with extended theoretical modelling, using Time Dependent Density Functional Theory (TD-DFT) and ab initio self-consistent multiple-scattering code (FEFF).