Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO 2 nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO 2 surfaces have a clean surface and clean interface between Pt and CeO 2 . Different growth behaviors of Pt on the two types of CeO 2 nanocrystals were observed, with epitaxial growth of Pt on CeO 2 nanooctahedra and random growth of Pt on CeO 2 nanorods. The structures of the Pt clusters on the two different types of CeO 2 nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The supportdependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO 2 nanorods showed much higher activity compared with Pt/CeO 2 nanooctahedra because of the higher concentration of oxygen vacancies in the CeO 2 nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO 2 nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.

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We have previously synthesized Cu/Pd nanoparticles with a citric complexing agent, demonstrating well the suspension and high catalytic ability of electroless copper deposition. Herein, we report the in situ investigation of the synthesis of Cu/Pd nanoparticles with a citric complexing agent by X-ray absorption near-edge structure (XANES). By characterizing the XANES spectra of Cu and Pd upon the stepwise addition of an alkaline solution, the reaction mechanism of Cu as well as Pd complexing ions was elucidated. Slow reduction of Pd ions and fast reduction of Cu ions induced by zerovalent Pd are found in XANES spectra. A three-stage formation mechanism of Cu/Pd nanoparticles was proposed in which a Pd reduction initial stage, a Cudominated reduction middle stage, and a Pd-dominated reduction final stage were indicated. As a result, a Pd-rich outer shell formed on the surface of synthesized Cu/Pd particles in the final stage. In summary, the formation mechanism and the Pd-rich outer shell structure of synthesized Cu/Pd nanoparticles were found in this citric complexing agent synthesis method.

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