The nucleation and growth of palladium clusters supported on anatase TiO 2 (101) surface has been studied using periodic supercell models and density functional theory. The most active site for single Pd adatom on the perfect TiO 2 (101) surface is the bridge site formed by two two-coordinated oxygen (2cO) atoms at the step edge with the highest adsorption energy of 2.18 eV. On the defective surface, the effect of oxygen vacancy on Pd nucleation is not as strong as that in the Pt or Au deposition case. The shift of active sites for the Pd dimer growing to trimer on the perfect anatase TiO 2 (101) surface is observed. On both perfect and defective anatase surfaces, the adsorbed Pd 3 clusters prefer to form planar triangles and the adsorbed Pd 4 and Pd 5 clusters tend to three-dimensional structures. The nucleation and growth of Pd clusters at the anatase TiO 2 (101) surface is mainly driven by the interaction between Pd and surface atoms when the cluster size is less than four. The strength of Pd-Pd interaction turns out to control dominantly the Pd deposition process as the Pd cluster gets larger.

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