Growth mechanism of palladium clusters on rutile TiO2(110) surface

Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal. Thus in this paper, we embark on a systematic study for Pdn (n = 1–5) clusters adsorbed on TiO2(110) surface based on DFT-GGA calculations utilizing periodic supercell models. A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction, while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface. According to the transition states (TSs) search, the adsorbed Pd trimer tends to triangular growth mode, rather than linear mode, while the Pd4 and Pd5 clusters prefer three-dimensional (3D) models. However, the oxygen vacancy has almost no influence on the promotion of Pdn cluster nucleation. Additionally, of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation, whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger. It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.