2, Universidad de Sonora, Hermosillo, Sonora, Mexico
3, Chalmers University of Technology, Gothenburg, , Sweden
One of the most technologically relevant application of oxide supported transition metals lies in heterogeneous catalysis. This is particularly true in emission control systems - such as the catalytic converter of automobiles - where they are usually highly dispersed and known to be oxidized under ambient conditions. One component in the automobile three-way catalytic converter is Pt/CeO2; where Pt serves to oxidize hydrocarbons and carbon monoxide, while ceria (CeO2) acts as an oxygen storage component. 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 PtN/CeO2(111) supported clusters.
In this talk, I will describe the implementation of an unbiased Density Functional Theory based global optimization Basin Hopping Monte Carlo algorithm (BH-DFT) to study growth trends of CeO2(111) supported PtN clusters. From our results, we observe a clear preference for planar 2D structures up to size Pt8, followed by a structural transition to 3D structures at size Pt9. This remarkable trend is explained by a subtle competition between the formation of strong Pt-O bonds and the cluster internal Pt-Pt bonds. Our calculations show the reducibility of CeO2(111) provides a mechanism to anchor PtN clusters where they become oxidized in a two-way charge transfer mechanism: (a) an oxidation process, where Osurface atoms withdraw charge from Pt atoms forming Pt-O bonds, (b) surface Ce4+ atoms are reduced to Ce3+. In this way, the active role of CeO2(111) support in modifying the structural properties and eventual chemical reactivity of sub-nanometer PtN clusters is computationally demonstrated. Finally, global optimization strategies in order to deal with bimetallic platinum-copper (Pt-Cu) supported clusters within our BH-DFT implementation will be also discussed.