Role of Cluster Morphology in the Dynamics and Reactivity of Subnanometer Pt Clusters Supported on Ceria Surfaces

We study subnanometer (sub-nm) Pt clusters supported by highly reducible oxide surfaces and establish the role of cluster morphology in the thermodynamics and kinetics of surface processes relevant for reactivity, namely cluster mobility, reverse oxygen spillover, and oxygen vacancy formation. The relationships between cluster morphology and reactivity are rarely considered in computational studies because of the large domain and complexity of the potential energy surface, particularly in the presence of strong metal–support interaction. Global optimization algorithms together with Hubbard-corrected density functional theory calculations (DFT+U) are used to identify the stable and metastable morphologies of Pt₃–Pt₆ clusters supported on pristine and defective CeO₂(111) surfaces. Our systematic exploration for these sub-nm Pt particles shows that the charge of the supported cluster, its bonding to the substrate, and the degree of ceria reduction depend on the metal/oxide interface area and on the cluster morphology. Concerning reaction thermodynamics and kinetics, the use of global optimization methods leads to very different results as compared to usual minimization procedures. By allowing for morphology changes during reaction, the energetics of reverse O spillover changes from highly endothermic to exothermic and leads to new minimum-energy reaction and diffusion mechanisms. The diffusion kinetics predicts clusters as small as Pt₆ to be resistant to sintering on ceria surfaces. The relevance of these findings for larger metal clusters and for supporting oxide nanoparticles is discussed as well as their connection with the recent literature