Ru³⁺ -mediated Synthesis Of Palladium Nanocrystals And Their Performance In Photodriven Catalytic Styrene Hydrogenation

Pd is the most active metal material for hydrogenation reactions, which is always the research focus for catalytic hydrogenation techniques. To improve its catalytic activity, a lot of efforts have been focused on the fabrication of Pd nanostructures with monodispersed sizes and well-defined morphologies. It is well known that the edge and corner atoms are the active sites for hydrogenation reactions. For this reason, the Pd nanocrystals with maximized edge and corner atoms would be ideal catalysts for hydrogenation reactions.In addition to the reaction activities of catalysts, the energy source is another important parameter to catalytic reactions. For this reason, attempts have been made to couple the solar energy into various catalytic organic reactions, by utilizing the surface plasmon properties of metal nanocrystals. However, the Pd nanoparticles that are synthesized in solution phase generally have small sizes, confining their plasmonic band in the UV spectral range. To tune their plasmonic band towards longer wavelengths, one can increase the particle sizes or lowering the shape symmetry of nanocrystals.The concave nanostructures possess a large number of atoms at corners and edges, which are generally believed to be active sites for hydrogenation. Moreover, they are of low symmetry as compared with spherical and cubic shapes. Taken together, the concave nanostructures with large particle sizes would be ideal candidates as plasmonic-driven catalysts for hydrogenation.In this dissertation, a Ru3+-mediated synthesis for the unique Pd concave nanostructures is described, which can directly harvest UV-visible light for styrene hydrogenation. The catalytic efficiency under 100 mWcm-2 full-spectrum irradiation at room temperature turns out to be comparable to that of thermally (70℃) driven reactions. In sharp contrast, other Pd nanostructures such as nanocubes and octahedrons offer much lower yields. The nanostructures reported here have sufficient plasmonic cross-sections for light harvesting in a broad spectral range owing to the reduced shape symmetry, which increases the solution temperature for the reaction by the photothermal effect. They possess a large quantity of atoms at corners and edges where local heat is more efficiently generated, thus providing active sites for the reaction. Taken together, these factors drastically enhance the hydrogenation reaction by light illumination.