Enhanced Chemical Reactivity of Under-Coordinated Atoms at Pt-Rh Bimetallic Surfaces: A Spectroscopic Characterization

The electronic structure and chemical reactivity changes of highly under-coordinated Rh atoms on a Pt(111) surface versus coordination number were studied by a combination of synchrotron radiation core level photoemission spectroscopy and density functional theory. The properties of Rh adatoms are strongly modified by the Pt substrate, when compared with the equivalent atomic configuration in the homometallic environment. A remarkable linear relationship is found between core level shifted spectral components, originating from different atomic geometrical structures, and the corresponding induced d-band center shifts. This finding strongly underscores the relevance of core level shifts as reliable experimental descriptors of chemical reactivity, also for under-coordinated atoms in bimetallic transition metal systems. The availability of an experimental tool capable of detecting local surface alloy configurations with enhanced chemical reactivity opens up the possibility to investigate more complex systems with high density of under-coordinated atoms, such as nanostructured multicomponent alloy surfaces and bimetallic nanoclusters.