Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe3O4 model catalyst

Z. Jakub, J. Hulva, P. T. P. Ryan, D. A. Duncan, D. J. Payne, R. Bliem, M. Ulreich, P. Hofegger, F. Kraushofer, M. Meier, M. Schmid, U. Diebold, G. S. Parkinson

Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK
Department of Materials, Imperial College London, South Kensington, London, SW7 2AZ, UK
University of Vienna, Faculty of Physics and Center for Computational Materials Science, 1090 Vienna, Austria

Nanoscale 12 (2020) 5866–5875

The structure of a catalyst often changes in reactive environments, and following the structural evolution is crucial for the identification of the catalyst's active phase and reaction mechanism. Here we present an atomic-scale study of CO oxidation on a model Rh/Fe3O4(001) "single-atom" catalyst, which has a very different evolution depending on which of the two reactants, O2 or CO, is adsorbed first. Using temperature-programmed desorption (TPD) combined with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we show that O2 destabilizes Rh atoms, leading to the formation of RhxOy clusters; these catalyze CO oxidation via a Langmuir–Hinshelwood mechanism at temperatures as low as 200 K. If CO adsorbs first, the system is poisoned for direct interaction with O2, and CO oxidation is dominated by a Mars-van-Krevelen pathway at 480 K.

Corresponding author: Gareth S. Parkinson (parkinson at iap_tuwien_ac_at).

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