(683f) Determining the Clustering Tendencies of Pt and Rh on a Cu2o Thin Film

Single-site catalysts are difficult to characterize because of their sensitivity to the coordination environment and metal-support interactions. Single-faceted model surfaces are often used to characterize metal-support interactions. The “29” oxide is a Cu₂O-like surface oxide that serves to atomically disperse dopant atoms, that interact with both metallic Cu and the copper oxide thin film. Our density functional theory (DFT) based model was used to investigate factors which influence dopant atom sintering tendencies on the “29” oxide and to correlate our results to the scanning tunneling microscopy (STM) measurements, where atomically dispersed Rh and clusters co-exist under ultrahigh vacuum (UHV) at 300 K while Pt adatoms are mostly isolated. We find that strong interaction with metallic Cu anchors Pt adatoms on the “29” oxide, giving rise to a higher rate-limiting barrier for the migration of the adatom. The oxophilic character of the precious metals promotes adatom migration, as interaction with oxide oxygen weakens its interaction with the metallic Cu substrate. The higher oxophilic character of Rh stabilizes Rh on a variety of sites on the “29” oxide, resulting in a shallower adsorption potential energy surface with minima closer in energies. Electronic distortion induced upon CO adsorption also weakens the interaction between the adatom with metallic Cu, even more so for the Rh adatom in the vicinity of an O adatom. This indicates that the higher oxophilicity of the adatom weakens its binding to metallic Cu. In addition to high mobility, larger cohesive forces between Rh adatoms contributes to a lower number of atoms threshold for the formation of Rh clusters. Our work demonstrates that metal oxophilicity, interaction to metallic Cu, as well as cohesive forces, all play critical roles toward the clustering tendencies on mixed Cu metal/oxide interfaces and highlights how they can impact the catalytic reactivity on oxidized Cu surfaces.