Structure-Reactivity Relationships
Prof. Dr. Angelika Brückner
PD Dr. habil. Wolfgang Baumann

In Topic 01, modern experimental methods are established and combined as an essential basis for knowledge-based catalyst design. This includes the development, optimization and application of innovative methods, processes and setups for carrying out catalytic reactions and catalyst syntheses. The aim is to accelerate the development of new catalytic processes and to make existing processes more efficient.  

One focus is on the development of new spectroscopic reaction cells in which different in situ and operando methods can be coupled simultaneously. Of particular note is the 5-in-1 coupling of FTIR-ATR/UV-Vis/EPR/EXAFS/XANES at a measurement site of the Synchrotron Soleil near Paris, which allows, for example, the elucidation of complex reaction mechanisms. In addition, a low temperature FTIR cell was developed to analyze exposed metal centers on the surface of solid catalysts by adsorption of probe molecules (NO, CO).

New experimental solutions were developed for operando spectroscopy at elevated pressure up to 20 bar. Worth mentioning here are the FTIR spectroscopic investigation of the Fischer-Tropsch synthesis with CO2 and the combination of EPR spectroscopy and EXAFS/XANES for mechanistic studies of the homogeneous chromium-catalyzed tetramerization of ethylene.

Further milestones on the way to relevant reaction conditions for in situ investigations of catalysts are (i) the installation of a new NAP-XPS spectrometer (Near Ambient Pressure) at LIKAT and (ii) an innovative TEM setup with special sample holders for in situ investigations at elevated temperatures and pressures at the interdisciplinary faculty 'Life, Light & Matter' of the University of Rostock (funds for this were jointly obtained). The measurements under near-real conditions allow conclusions to be drawn, for example, about reaction conditions or catalyst properties that need to be adjusted.

The comprehensive set of operando techniques has been used for monitoring selective oxidations, hydrogenations, photocatalytic as well as environmentally relevant reactions such as selective catalytic reduction of NOx (NH3-SCR) and photocatalytic ozonation of organic contaminants in wastewater.
A very illustrative example of the collaboration between different groups in Topic 01 is the development of a special 'spin-trapping' method in the research group 'Magnetic Resonance & X-ray Methods', which can selectively distinguish between different radicals. With the help of this method, predominantly preparative groups can detect whether reactions are driven by radical mechanisms.
Investigation of structural and electronic properties of heterogeneous and homogeneous photocatalyst and electrocatalyst systems in CO2 reduction, water splitting, and methanol oxidation revealed that known active sites from thermal catalysis can possess comparable activities in the novel reaction guides. The collaboration in Topic 01 enabled a more detailed investigation of these findings in temperature-dependent UV-Vis and Raman measurements and the deciphering of the relationships between optical, electronic and catalytic properties of the material.
In the future, the combination of operando FTIR spectroscopy and kinetics as well as chemometrics will be a new experimental advance in the subject area.