Atomic-scale investigations of MoS2-based catalysts
Single atom catalysis has emerged in recent years as a promising approach to develop cost effective heterogeneous catalysts and electrocatalysts. While metal oxides were initially the support of choice, anchoring single atoms on 2D materials presents an opportunity to create a unique active site with properties not found elsewhere . MoS2 has attracted attention because it is already an active catalyst for several reactions, but activity is often restricted to specific edge sites. Doping the terraces with foreign metal atoms offers a route to increase the active site density, and theory suggests metals such as Pt can substitute both Mo and S in the MoS2 structure . Little is known about how the unusual coordination environment affects the properties of the metal, how this translates into catalytic properties, and whether such catalysts remain stable in realistic conditions.
© Gareth Parkinson
Left: DFT-derived structure of the Au1/Fe3O4 model single atom catalyst systems utilized in the Parkinson group. Right: TEM image of Pt adatom incorporated in a S vacancy in monolayer MoS2.
This project aims to study whether MoS2 can be an effective support for catalytically active metal atoms and clusters, and to determine the atomic-scale structure of the potentially stable structures in UHV. We will correlate the structure to the reactivity of the model systems, and then study their stability and catalytic activity in progressively more realistic ambient pressure and electrochemical environments.
Procedures to grow MoS2 using CVD in UHV are well established in the surface science literature. We will dope the films with metals such as Rh, Ir, Pt, and investigate the site using atomically resolved SPM. With the structure known, we will perform temperature programmed desorption experiments using various probe molecules (CO, H2O, CO2) to understand how the addition of the metal changes the reactivity of the catalyst. We recently built a state of the art molecular-beam-based surface chemistry setup  which will be ideal for these experiments. The surface chemistry chamber also allows several other complementary techniques including photoelectron spectroscopies, ion scattering, and infrared absorption spectroscopy, to be performed on the same sample over a temperature range of 30 - 1200 K. The latter technique will allow direct comparison to the DRIFS experiments performed over similar systems in the project of Eder. Finally, we will study the stability of the systems in realistic environments using recently developed high-pressure reaction- and electrochemical cells directly interfaced to our UHV setups.
The PhD student will collaborate with the Diebold project to create and characterize defects in 2D materials in UHV. We will then investigate their use in anchoring metal adatoms to create model SAC systems. Pichler will provide complementary optical measurements.Our surface science studies ideally complement theory because measured bond lengths and binding energies can be used to benchmark the simulation. As such, we will work closely with Madsen and Libisch to understand how metal atoms are stabilized by MoS2, and how this affects the reactivity. Moreover, we will work with Eder to correlate the performance of real MoS2-based SACs using our fundamental insights. Filipovic will use our temperature programmed adsorption results to quantify the concentration of adsorbed gas molecules in the MoS2 conductivity model.
Gareth Parkinson focuses on understanding catalytic reactions at the atomic scale. He studies well-characterised model systems combining scanning-probe microscopies, quantitative structural determinations, and high-resolution spectroscopies. He has pioneered the use of single crystal model supports for ``single-atom'' catalysis (SAC) : the (001) surface of magnetite stabilizes metal adatoms up to 700K, enabling the study of fundamental processes in SAC. He built a multi-technique vacuum system to study the catalytic activity of SAC systems . He was awarded an ERC consolidator grant in 2020.
- J. Pavelec, J. Hulva, D. Halwidl, R. Bliem, O. Gamba, Z. Jakub, F. Brunbauer, M. Schmid, U. Diebold, and G. S. Parkinson. A multi-technique study of CO2 adsorption on Fe3O4 magnetite. The Journal of Chemical Physics 146, 014701 (2017). DOI: 10.1063/1.4973241.
- H. Li, S. Wang, H. Sawada, G. G. D. Han, T. Samuels, C. S. Allen, A. I. Kirkland, J. C. Grossman, and J. H. Warner. Atomic structure and dynamics of single platinum atom interactions with monolayer MoS2. ACS Nano 11, 3392–3403 (2017). DOI: 10.1021/acsnano.7b00796.
- G. S. Parkinson. Single-atom catalysis: How structure influences catalytic performance. Catalysis Letters 149, 1137–1146 (2019). DOI: 10.1007/s10562-019-02709-7.