Fine Control over the Compositional Structure of Trimetallic Core-Shell Nanocrystals for Enhanced Electrocatalysis.

Pt-based multimetallic nanocrystals (NCs) have attracted tremendous research interest because of their excellent catalytic properties in various electrocatalysis fields. However, the development of rational synthesis approaches that can give multimetallic NCs with desirable compositional structures is still a radical issue. In the present work, we devised an efficient strategy for the systematic control of the spatial distribution of constituent elements in Pt-based trimetallic core-shell NCs, through which NCs with distinctly different compositional structures, such as Au@PdPt, Au@Pd@Pt, AuPd@Pt, and AuPdPt@Pt core-shell NCs, could selectively be generated. The adjustment of the amount of a reducing agent, hydrazine, which can provide control over the relative reduction kinetics of multiple metals, is the key to the selective formation of NCs. Through extensive studies on the effect of the compositional structure of the trimetallic NCs on their catalytic function toward the methanol electro-oxidation reaction, we found that the Au@Pd@Pt NCs exhibited considerably enhanced catalytic performance in comparison to the other trimetallic NCs as well as to their binary counterparts, a commercial catalyst, and reported Pt-based nanocatalysts due to the optimized surface electronic structure. The present strategy will be useful to design and construct multicomponent catalytic systems for various energy and environmental applications.

Shape and Composition Control of Monodisperse Hybrid Pt-CoO Nanocrystals by Controlling the Reaction Kinetics with Additives.

Here, we report the effect of Fe(CO)5 additives in the synthesis of branched Pt-CoO nanowires (NWs) and core@shell concave nanocubes (NCs), in a one-pot system. Key to the success of this synthesis is control over the shape of the Pt seeds by controlling the quantity of Fe(CO)5 additive. In the absence of Fe(CO)5, branched Pt-CoO NWs were synthesized through the attachment of small Pt seed particles, followed by the growth of CoO by deposition. On the other hand, Pt@CoO concave NCs were obtained in the presence of Fe(CO)5 because of the stronger adsorption of Co on the Pt (100) surfaces than on the closely packed (111) surfaces. Also, various other conditions including the control of reducing agents, precursor concentrations, and stabilizing agents, were used to verify the effects of reaction kinetics on the synthesis of Pt-CoO nanoparticles. Compared to Pt/graphene oxide (GO) catalyst, branched Pt-CoO NWs supported on GO showed enhanced specific activity toward the oxygen reduction reaction (ORR).

Shape-Controlled Synthesis of Dumbbell-like Pt-Fe3O4-MnO x Nanoparticles by Governing the Reaction Kinetics.

The production of shape-controlled heterometallic nanoparticles (NPs) consisting of Pt and nonprecious metal oxides is crucial to demonstrate the composition-property relationship of NPs. Herein, we report a facile one-pot approach for the controlled synthesis of dumbbell-like Pt-Fe3O4-MnO x and dendritic Pt-MnO x NPs. The key to the success of this synthesis is in changing the quantity of Fe(CO)5 additive to control the reaction kinetics. In the absence of Fe(CO)5, dendritic Pt-MnO x NPs were synthesized through the assembly of small seed NPs. On the other hand, dumbbell-like Pt-Fe3O4-MnO x NPs were obtained in the presence of Fe(CO)5 through controlling the nucleation and growth of Fe and Mn on the Pt NPs, followed by air oxidation. Compared to a Pt/graphene oxide (GO) catalyst, dumbbell-like Pt-Fe3O4-MnO x NPs on GO showed an enhancement of specific activity toward the oxygen reduction reaction owing to the compressive-strain effect exerted on the Pt lattice.

Rose-like Pd-Fe3O4 hybrid nanocomposite-supported Au nanocatalysts for tandem synthesis of 2-phenylindoles.

A facile synthesis of rose-like Pd-Fe3O4 nanocomposites via controlled thermal decomposition of Fe(CO)5 and reduction of Pd(OAc)2, followed by the immobilization of Au nanoparticles (NPs) onto the Pd-Fe3O4 supports, is reported. The morphology of these hybrid nanostructures could be easily controlled by varying the amount of Fe(CO)5 and the reaction temperature. Moreover, the synthesized Au/Pd-Fe3O4 catalyst exhibited high catalytic activity for the tandem synthesis of 2-phenylindoles and demonstrated magnetic recyclability.

Magnetically separable and recyclable Fe3O4-supported Ag nanocatalysts for reduction of nitro compounds and selective hydration of nitriles to amides in water.

As hybrid nanostructures have become more important in many fields of chemistry, Ag nanoparticles (NPs) are being increasingly immobilized onto Fe3O4 microspheres in situ. Structural characterization reveals that the Ag NPs are uniformly immobilized in the Fe3O4 microsphere-based supports. Moreover, Ag NPs are more stable in the hybrid structure than in the naked state and show high catalytic activity for the reduction of nitro compounds and hydration of nitriles to amides in water. The Fe3O4 microspheres were recycled several times using an external magnet.

CuO hollow nanosphere-catalyzed cross-coupling of aryl iodides with thiols.

New functionalized CuO hollow nanospheres on acetylene black (CuO/AB) and on charcoal (CuO/C) have been found to be effective catalysts for C-S bond formation under microwave irradiation. CuO catalysts showed high catalytic activity with a wide variety of substituents which include electron-rich and electron-poor aryl iodides with thiophenols by the addition of two equivalents of K2CO3 as base in the absence of ligands.

Azide-alkyne Huisgen [3+2] cycloaddition using CuO nanoparticles.

Recent developments in the synthesis of CuO nanoparticles (NPs) and their application to the [3+2] cycloaddition of azides with terminal alkynes are reviewed. With respect to the importance of click chemistry, CuO hollow NPs, CuO hollow NPs on acetylene black, water-soluble double-hydrophilic block copolymer (DHBC) nanoreactors and ZnO–CuO hybrid NPs were synthesized. Non-conventional energy sources such as microwaves and ultrasound were also applied to these click reactions, and good catalytic activity with high regioselectivity was observed. CuO hollow NPs on acetylene black can be recycled nine times without any loss of activity, and water-soluble DHBC nanoreactors have been developed for an environmentally friendly process.