"Single-Atom" Catalysis

The field of “Single-Atom” catalysis came about from attempts to downsize the precious metal component of heterogeneous catalyst. In the ultimate limit, isolated adatoms attach to a support material through chemical bonds, which affects the electronic structure, and through it, the reactivity of the metal. Thus, it is no longer really clear which metal will be best for a particular reaction, and there is much work to be done to understand how SAC systems behave. Interestingly, a single metal centre bound to “surface ligands” bears some resemblance to the highly selective coordination complexes used in homogeneous catalysis, and there is growing excitement that single atom catalysis could bridge the gap between these fields and lead to a new generation of highly efficient and selective heterogeneous catalysts. Our group is contributing to such efforts, and given substantial research funding from the FWF and ERC, we will be doing so for some time to come.

Initially our work utilized the (001) surface of magnetite (Fe₃O₄), which exhibits a remarkable reconstruction that stabilizes dense arrays of metal adatoms. Subsequent work has shown that this beautiful model system is limited because the reconstruction does not persist outside the vacuum chamber, so we have begun to look for more realistic models to study reactions in realistic conditions.

2 million euros over 5 years. Project abstract:

Rare and expensive metals tend to make the best heterogeneous catalysts, and minimising or replacing these materials is a major research target as we strive to develop an economy based on more environmentally-friendly, energy-efficient technologies. “Single-atom” catalysis (SAC) represents the ultimate in efficiency, and the chemical bonds formed between the metal atom and the support mean these systems strongly resemble the organometallic complexes utilized in homogeneous catalysis. If all active sites were identical, SACs could achieve similar levels of selectivity, and even be used to “heterogenize” difficult reactions that must be currently performed in solution. There is a problem however: homogeneous catalysts are designed based on well-understood structure-function relationships. In SAC, the structure of the active site is unknown, thus rational design is impossible. My group in Vienna has pioneered the use of the model supports to understand fundamental mechanisms in SAC. Our work with Fe3O4(001) proves that we can precisely determine and even selectively modify the active site, and unravel the role of structure in catalytic activity. Real progress, however, requires realistic active sites, realistic supports, and realistic environments. In this project, I describe how we will determine the sites that robustly anchor metal atoms on five of the most important supports in UHV, and test their performance in newly-developed high-pressure and electrochemical cells. The origins of selectivity for PROX, hydrogenation, hydroformylation, methane conversion, and the oxygen reduction reaction (ORR) will be determined, and the best atom/support combinations for each reaction identified. Robust XANES and IRAS spectra will allow us to bridge the complexity gap and recreate the optimal active sites on real SACs and lead the way into a new era in which heterogeneous catalysts are designed for purpose, based on a fundamental understanding of how they work.

1. Florian Kraushofer, Nikolaus Resch, Moritz Eder, Ali Rafsanjani-Abbasi, Sarah Tobisch, Zdenek Jakub, Giada Franceschi, Michele Riva, Matthias Meier, Michael Schmid, Ulrike Diebold, Gareth S. Parkinson
   Surface Reduction State Determines Stabilization and Incorporation of Rh on α-Fe2O3(11 ̅02)
   Advanced Materials Interfaces special issue on Single-Atom Catalysis, in press
2. Jan Hulva, Matthias Meier, Roland Bliem, Zdenek Jakub, Michael Schmid, Ulrike Diebold, Cesare Franchini, Gareth S. Parkinson
   Unravelling CO Adsorption on Model Single-Atom Catalysts
   Science 371 (2021) 375-379
3. Zdenek Jakub, Jan Hulva, Matthias Meier, Roland Bliem, Florian Kraushofer, Martin Setvin, Michael Schmid, Ulrike Diebold, Cesare Franchini, Gareth S. Parkinson
   Local Structure and Coordination Effects Define Adsorption in a Model Ir1/Fe3O4 Single-Atom Catalyst
   Angewandte Chemie International Edition 58, 13961-13968 (2019)
4. G. S. Parkinson
   Single-Atom Catalysis: How Structure Influences Catalytic Performance
   Catalysis Letters 149, 1137 (2019)
5. Roland Bliem, Jessi van der Hoeven, Adam Zavodny, Oscar Gamba, Jiri Pavelec, Petra E de Jongh, Michael Schmid, Ulrike Diebold, Gareth S Parkinson
   Dual role of CO in the stability of sub-nano Pt clusters at the Fe3O4(001) surface
   PNAS 113, (2016) 8921
6. Roland Bliem, Jessi van der Hoeven, Adam Zavodny, Oscar Gamba, Jiri Pavelec, Petra E de Jongh, Michael Schmid, Ulrike Diebold, Gareth S Parkinson
   An Atomic‐Scale View of CO and H2 Oxidation on a Pt/Fe3O4 Model Catalyst
   Angewandte Chemie International Edition 54 (47), 13999-14002 (2016)
7. G.S. Parkinson, Z. Novotny, G. Argentero, M. Schmid, J. Pavelec, R. Kosak, P. Blaha, U. Diebold
   Carbon monoxide-induced adatom sintering in a Pd-Fe3O4 model catalyst
   Nature Mater. 12 (2013) 724
8. Z. Novotný, G. Argentero, Z. Wang, M. Schmid, U. Diebold, G. S. Parkinson
   Ordered Array of Single Adatoms with Remarkable Thermal Stability: Au/Fe3O4(001)
   Phys. Rev. Lett. 108 (2012) 216103 ⋅ full text

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