Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 75: Fundamentals of Catalysis I

O 75.8: Vortrag

Donnerstag, 4. April 2019, 12:30–12:45, H5

Bimetallic PdPt Alloy Nanocluster Arrays on Graphene/ Rh(111): Formation, Stability, and Dynamics — •Fabian Düll, Udo Bauer, Florian Späth, Philipp Bachmann, Johann Steinhauer, Hans-Peter Steinrück, and Christian Papp — Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander- Universität Erlangen-Nürnberg, Germany

Alloy catalysts often have superior properties compared to their single metal counterparts. We studied bimetallic PdPt alloy nanocluster arrays supported on a chemically inert graphene/Rh(111) Moiré. The clusters are well-ordered, separated, and have a small size distribution; thus, they are an intriguing model system for catalysis bridging the materials gap by introducing various facet and edge sites. Using in situ high-resolution XPS, we followed the site occupation and dynamic changes of the metal distribution during CO adsorption and thermal treatment [PCCP, 2018, 20, 21294]. Annealing of the as-prepared nanoclusters after exposure to CO to 550 K leads to a restructuring towards a more 3D shape and to a replacement of Pt atoms at the cluster edges by Pd. The facets are dominated by Pt. Additionally, the nanoclusters are stabilized, as repeated CO adsorption and desorption cycles cause no further changes. Interestingly, we observe dynamical changes during heating or when applying a CO- or O2-stream at constant temperatures: CO molecules rearrange from terrace to edge sites, and Pt atoms move back to the particle edges. These effects are only found at elevated temperatures in the presence of CO and disappear when the system cools down in a vacuum.