Theoretical study of ripening mechanisms of Pd clusters on Ceria

We carried out density functional theory calculations to investigate the ripening of Pd clusters on CeO2(111). Starting from stable Pdn clusters (n=1-21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have a high mobility than Pd¬n clusters on the CeO2(111) surface, Ostwald-ripening is predicted to be the dominant sintering mechanism. Particle coalescence is only possible when very small clusters with less than 5 Pd at-oms are involved. These ripening mechanisms are facilitated by adsorbed CO through lowering barriers for the cluster diffusion, detachment of a Pd atom from clusters, and transformation of initial planar clusters.