Fritz-Haber-Institut der Max-Planck Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
The investigation of model systems has successfully demonstrated that surface science results may be directly transferred to heterogeneous catalysis under realistic conditions, and it offers an approach to correlate structural and electronic information at the atomic level with reactivity. An approach to model oxide-supported metal catalysts using a thin film approach is presented. Here the oxide support is prepared as a thin oxide film on a metal support, which guarantees the applicability of the tool-box of surface science even in the case nominally insulating substrates and metal particles are grown via physical vapor deposition1. Three conceptual studies are presented: 1) A phenomenon in heterogeneous catalysis when reducible oxide supported metal nano-particles get oxide encapsulated is called strong metal support interaction (SMSI). How such particles participate in catalytic reaction is still under strong debate. We demonstrate how a combination of surface science techniques allows us to unravel the active sites on the encapsulating oxide in such systems2. 2) The sites at the oxide-metal interface are of particular interest, as they are often held responsible to present the active site. Au particles supported on an MgO(100)/Mo(100) have been predicted to get negatively charged. It is shown that this prediction is verified and reactivity is induced at the metal particle rim3-5. It is discussed how this scenario may be used to control charge on powder supported metal catalysts6. 3) In the third part of the presentation we discuss how surface science studies may be employed to understand fundamental issues with respect to reaction in confined space: A thin silica film is prepared on a Ru(0001) surface and is only bound to the substrate by dispersive forces and thus leaves a space open between the metal surface and the oxide film to use our SMART-LEEM/PEEM instrument to follow the oxidation of hydrogen provided from the gas phase by oxygen adsorbed on the Ru(0001) surface7. The experimental results are discussed in comparison to theoretical calculations8,9.
1 H.-J. Freund; J.Amer.Chem.Soc. 138, 8985 (2016)
2 K. Zhang et al.; Angew. Chem. Int. Ed. 57, 1261 (2018)
3 F. Calaza et al.; Angew.Chem.Int.Ed. 54, 12484 (2015)
4 Ch. Stiehler et al.; Phys.Rev.Lett. 115, 0368041 (2015)
5 Y. Cui et al.; Phys.Rev.Lett. 114, 016804 (2015)
6 X. Shao et al.; Angew.Chem. Int. Ed. 50, 11525 (2011)
7 M. Prieto et al.; Angew. Chem.Int.Ed. 57, 8749 (2018)
8 T. Mullan, D. Usvyat, J. Sauer et al. Unpublished
9 M. Schlutow et al. Unpublished
Hans-Joachim Freund is a scientific member and director at the Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlin where he is head of the Department of Chemical Physics. The department is dedicated to the study of model catalysts, applying a large number of techniques and instruments, some of which were newly developed within the department to investigate oxide surfaces and oxide metal interfaces. He serves as Adjunct Professor at five universities in Germany and UK. He received awards in Europe, the US, and Asia. He is a member of six Academies including the German National Academy of Sciences Leopoldina and the American Academy of Arts and Sciences and holds three honorary Doctorates. He received the Gaede-Langmuir Award of the American Vacuum Society and is the recipient of the 2015 Michel Boudart for the Advancement of Catalysis by the North American Catalysis Society and the European Federation of Catalysis Societies. He is Fellow of the American Physical Society and has published more than 815 scientific papers with more than 45.000 citations and given about 770 invited talks. He has held a number of named lectureships around the world. He has educated more than 130 PhD students and collaborated with more than 80 postdoctoral associates.