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The shape control of noble metal nanocrystals is crucial to their optical properties and catalysis applications. In this Progress Report, the recent progress of shape-controlled synthesis of Pd and Pt nanostructures assisted by small adsorbates is summarized. The use of small strong adsorbates (e.g., I(-) , CO, amines) makes it possible to fabricate Pd and Pt nanostructures with not only well-defined surface structure but also morphologies that have not been achieved by other synthetic strategies. The roles of small adsorbates in shape control of Pd and Pt nanocrystals are discussed in the Report. Also presented in the Report are unique optical and catalytic properties of several Pd and Pt nanostructures (e.g., ultrathin Pd nanosheets, concave Pt octapod, concave Pd tetrahedra), as well as their bioapplications, to demonstrate the power of using small strong adsorbates in the shape control of Pt and Pd nanostructures., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Abstract: Electrochemical conversion of CO2 into fuels using electricity generated from renewable sources helps to create an artificial carbon cycle. However, the low efficiency and poor stability hinder the practical use of most conventional electrocatalysts. In this work, a 2D hierarchical Pd/SnO2 structure, ultrathin Pd nanosheets partially capped by SnO2 nanoparticles, is designed to enable multi‐electron transfer for selective electroreduction of CO2 into CH3OH. Such a structure design not only enhances the adsorption of CO2 on SnO2, but also weakens the binding strength of CO on Pd due to the as‐built Pd–O–Sn interfaces, which is demonstrated to be critical to improve the electrocatalytic selectivity and stability of Pd catalysts. This work provides a new strategy to improve electrochemical performance of metal‐based catalysts by creating metal oxide interfaces for selective electroreduction of CO2. [ABSTRACT FROM AUTHOR]

The fabrication of catalytically stable nanocatalysts containing fine noble metal nanoparticles is an important research theme. We report a method for the synthesis of a hierarchically structured Pd@hm-CeO2 multi-yolk-shell nanocatalyst (h=hollow; m=mesoporous) containing sub-10 nm Pd nanoparticles from pre-made hydrophobic Pd nanoparticles. In the developed method, monodisperse hydrophobic Pd nanoparticles are first reacted with an iron oxide precursor iron(III) acetylacetonate to allow the deposition of iron oxide on their surface. In a Brij 56-water-cyclohexane reverse micelle system, the surface growth of iron oxide is found to mediate and, thus, facilitate the encapsulation of hydrophobic Pd nanoparticles in SiO2 to yield Pd-Fe2O3@SiO2 nanoparticles in a high concentration. After removal of Fe2O3 by acid, the obtained Pd@SiO2 core-shell particles are reacted solvothermally with Ce(NO3)3 in an ethylene glycol-water-acetic acid mixture to produce multi-core-shell Pd@SiO2@m-CeO2 nanospheres. In each multi-core-shell Pd@SiO2@m-CeO2 nanosphere, several Pd@SiO2 particles are separately embedded in mesoporous CeO2. After selective removal of silica by NaOH, Pd@SiO2@m-CeO2 nanospheres are transformed into the multi-yolk-shell Pd@hm -CeO2 nanocatalyst. Even with a low Pd loading at 0.4 wt %, the as-prepared multi-yolk-shell Pd@hm-CeO2 nanocatalyst displays high catalytic activity in CO oxidation with 100 % CO conversion at 110 °C. In comparison, under the same catalytic conditions, the same amount of the same-sized Pd nanoparticles supported on SiO2 achieves 100 % CO conversion at 180 °C. More importantly, the multi-yolk-shell structure of the Pd@hm -CeO2 nanocatalyst significantly enhances the stability of the catalyst. No loss in catalytic activity was observed on the Pd@hm -CeO2 nanocatalyst treated at 550 °C for six hours. The Pd@hm -CeO2 nanocatalyst also exhibited excellent catalytic performance and stability in the aerobic selective oxidation of cinnamyl alcohol to cinnamaldehyde. [ABSTRACT FROM AUTHOR]

The fabrication of catalytically stable nanocatalysts containing fine noble metal nanoparticles is an important research theme. We report a method for the synthesis of a hierarchically structured Pd@hm-CeO2 multi-yolk-shell nanocatalyst (h=hollow; m=mesoporous) containing sub-10 nm Pd nanoparticles from pre-made hydrophobic Pd nanoparticles. In the developed method, monodisperse hydrophobic Pd nanoparticles are first reacted with an iron oxide precursor iron(III) acetylacetonate to allow the deposition of iron oxide on their surface. In a Brij 56-water-cyclohexane reverse micelle system, the surface growth of iron oxide is found to mediate and, thus, facilitate the encapsulation of hydrophobic Pd nanoparticles in SiO2 to yield Pd-Fe2O3@SiO2 nanoparticles in a high concentration. After removal of Fe2O3 by acid, the obtained Pd@SiO2 core-shell particles are reacted solvothermally with Ce(NO3)3 in an ethylene glycol-water-acetic acid mixture to produce multi-core-shell Pd@SiO2@m-CeO2 nanospheres. In each multi-core-shell Pd@SiO2@m-CeO2 nanosphere, several Pd@SiO2 particles are separately embedded in mesoporous CeO2. After selective removal of silica by NaOH, Pd@SiO2@m-CeO2 nanospheres are transformed into the multi-yolk-shell Pd@hm -CeO2 nanocatalyst. Even with a low Pd loading at 0.4 wt %, the as-prepared multi-yolk-shell Pd@hm-CeO2 nanocatalyst displays high catalytic activity in CO oxidation with 100 % CO conversion at 110 °C. In comparison, under the same catalytic conditions, the same amount of the same-sized Pd nanoparticles supported on SiO2 achieves 100 % CO conversion at 180 °C. More importantly, the multi-yolk-shell structure of the Pd@hm -CeO2 nanocatalyst significantly enhances the stability of the catalyst. No loss in catalytic activity was observed on the Pd@hm -CeO2 nanocatalyst treated at 550 °C for six hours. The Pd@hm -CeO2 nanocatalyst also exhibited excellent catalytic performance and stability in the aerobic selective oxidation of cinnamyl alcohol to cinnamaldehyde. [ABSTRACT FROM AUTHOR]