Heterogeneous catalysis is key for the future sustainable synthesis of chemicals and fuels, clean air and the mitigation of waste in chemical reactions. This is also closely related to the reduction of CO2-emissions and the energy transition, which are game changers for today’s energy landscape: renewable energy sources like wind and sun fluctuate, which consecutively also alter the reactions conditions. Therefore, a new generation of highly stable and active catalyst materials is needed. The major challenge during the development of catalytic processes is that the catalyst under working conditions is no longer the same as when it was designed and prepared . The structure of catalysts and their surface change dynamically – and this on different time and length scales. Such knowledge is crucial if catalysts are designed in a knowledge-based manner, e.g. by using computational predictions, and is thus topic of the two recently established coordinative initiatives SPP2080 “DynaCat”  and the CRC1441 “TrackAct” . Synchrotron light as basis for a thorough catalyst characterization is hereby essential for a rational design and with each generation of new synchrotron techniques a new impetus has been found to catalysis .
On the atomic scale bond breaking and formation as well as movement of atoms occurs in the ps to fs-scale . On the other end sintering of particles may occur on an hour, day or even month scale . Also the length scales are vast: In the first case we face processes on the nm-scale, in the other case it can be effects on the nm-scale but it may also be important to consider changes on the µm or even mm-scale. Notably, the active site is also not a single atom but is heavily dependent on the environment. It may be part of an entity (cluster, particle), it may be supported on a carrier, and it is often structured on a µm, mm and even cm scale. These different complexity scales need to be fully understood.
For this purpose, the present and upcoming X-ray sources with its complementary portfolio of techniques are ideal. They allow to cover better and better the various complexity scales in terms of time (from the fs scale up to hours) and length (atomic scale information to mm/cm/m-scale). The understanding of catalysis can be especially furthered with X-ray techniques due to their high penetration length. These challenges will be demonstrated with examples from energy-related catalysis including CO2-conversion to methanol and synthetic fuels, from green chemistry and from emission control (some example studies in ref. ).
 K.F. Kalz, R. Kraehnert, M. Dvoyashkin, R. Dittmeyer, R. Gläser, U. Krewer, K. Reuter, J.-D. Grunwaldt, “Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions”, ChemCatChem 9, 17-29 (2017).
 DFG Priority Program SPP2080, www.spp2080.org
 Collaboration Research Center CRC1441, www.trackact.kit.edu
 A. Nilsson et al., “Catalysis in real time using X-ray lasers”, Chem. Phys. Lett. 675, 145-173 (2017).
 D.I. Sharapa et al., Adv. Mater. 31, 1807381 (2019); A.R. Fahami et al., React. Chem. Eng., 4, 1000-1018 (2019); J. Becher et al., Nature Catal., 4, 46-53 (2021).; M.-A. Serrer et al., Catal. Sci. Technol., 10, 7542–7554 (2020); M. Loewert, M.-A. Serrer et al., React. Chem. Eng. 5 1071-1082 (2020); F. Maurer et al. Nature Catal. 3, 824-833 (2020).
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