Associate professor Gareth S. Parkinson, Institute of Applied Physics, TU Wien, Austria

Single Atom Catalysis: An Atomic Scale View

Single-atom catalysis is a rapidly emerging area of research that aims to maximize the efficient usage of precious metals through "signle atom" active sites. Although catalytic activity has been demonstrated for several single-atom catalyst systems, an inability to accurately characterize such a catalyst ensures that that the field remains controversial, and little is really known about how a single atom adsorbed on a metal oxide support catalyzes a chemical reaction.

In this lecture, I will describe how we are addressing the crucial issues of stability and reaction mechanism using a surface science approach. The work is based on the magnetite (001) surface, which exhibits an unusual reconstruction based on subsurface cation vacancies¹, stabilizes ordered arrays of metal adatoms (of almost any variety) with a nearest neighbor distance of 0.84 nm to unprecedented temperatures as high as 700 K^2,3. Because the geometry of the adatoms is uniform and precisely known, reactivity experiments are performed on a well-defined model system, and theoretical calculations can be performed to shed light on the mechanisms at work. Several examples of our recent work will be used to illustrate the trends discovered to date, including how strong CO adsorption destabilizes Pd and Pt adatoms leading to rapid sintering^4,5, how extraction of lattice oxygen from the metal-oxide is central to catalytic activity in the CO oxidation reaction⁶, and how partially dissociated water agglomorates⁷ that form on this surface can influence the reactivity.

1  Bliem, R. et al. Subsurface cation vacancy stabilization of the magnetite (001) surface. Science 346, 1215-1218 (2014).
2  Novotný, Z. et al. Ordered Array of Single Adatoms with Remarkable Thermal Stability: Au/Fe₃O₄(001). PRL 108, 216103 (2012).
3  Bliem, R. et al. Cluster Nucleation and Growth from a Highly Supersaturated Adatom Phase: Silver on Magnetite. ACS Nano 8, 7531-7537 (2014).
4  Bliem, R. et al. Dual role of CO in the stability of subnano Pt clusters at the Fe₃O₄(001) surface. PNAS 113, 8921-8926 (2016)
5  Parkinson, G. S. et al. Carbon monoxide-induced adatom sintering in a Pd–Fe₃O₄ model catalyst. Nature Mater 12, 724-728 (2013)
6  Bliem, R. et al. An Atomic-Scale View of CO and H2 Oxidation on a Pt/Fe3O4 Model Catalyst. Angewandte Chemie 54, 13999-14002 (2015)
7. Meier, M. et al. Water agglomerates on Fe₃O₄(001). PNAS (2018)

Host: Associate professor Jeppe Vang Lauritsen, iNANO & Dept. of Physics and Astronomy, Aarhus University