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 Pd n clusters (n = 1–21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have mobility higher than that of Pd n clusters on the CeO2(111) surface, Ostwald ripening is predicted to be the dominant sintering mechanism. Particle coalescence is possible only for clusters with less than 5 Pd atoms. 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.