Fundamental Studies Using a Surface Science Approach
© Gareth Parkinson/IAP
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.
- F. Kraushofer, G. S. Parkinson
Single-atom catalysis: Insights from model systems
Chemical Reviews 122, 14911 (2022); doi: 10.1021/acs.chemrev.2c00259
G. S. Parkinson
Single-atom catalysis: How structure influences catalytic performance
Catalysis Letters 149, 1137 (2019); doi: 10.1007/s10562-019-02709-7
ERC Consolidator Grant - Evolving Single-Atom Catalysis: Fundamental Insights for Rational Design
This project of Gareth Parkinson has a volume of 2 million euros over 5 years.
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.
Univ.Prof. Gareth Parkinson PhD
Head, Research Unit of Surface Physics