2D-3D structural transition in sub-nanometer Pt clusters supported on CeO(111).

Transition metal particles dispersed on oxide supports are used as heterogeneous catalysts in numerous applications. One example is platinum clusters supported on ceria which is used in automotive catalysis. Although control at the nm-scale is desirable to open new technological possibilities, there is limited knowledge both experimentally and theoretically regarding the geometrical structure and stability of sub-nanometer platinum clusters supported on ceria. Here we report a systematic, Density Functional Theory (DFT) study on the growth trends of CeO(111) supported Pt clusters (N = 1-10). Using a global optimization methodology as a guidance tool to locate putative global minima, our results show a clear preference for 2D planar structures up to size Pt. It is followed by a structural transition to 3D configurations at larger sizes. This remarkable trend is explained by the subtle competition between the formation of strong Pt-O bonds and the cluster internal Pt-Pt bonds. Our calculations show that the reducibility of CeO(111) provides a mechanism to anchor Pt clusters where they become oxidized in a two-way charge transfer mechanism: (a) an oxidation process, where O atoms withdraw charge from Pt atoms forming Pt-O bonds, (b) surface Ce atoms are reduced, leading to Ce. The active role of the CeO(111) support in modifying the structural and eventually the chemical properties of sub-nanometer Pt clusters is computationally demonstrated.