Hyunje Woo

Ordered Mesoporous Carbon Supported Colloidal Pd Nanoparticle Based Model Catalysts for Suzuki Coupling Reactions: Impact of Organic Capping Agents

Recent advances in the field of nanoscience have enabled the preparation of high‐surface‐area supported catalysts with precise control over the individual structural components. As such, a range of factors that affect the catalytic reactivity, such as the size, shape, and composition of the nanoparticles (NPs), have been identified. Herein, high‐surface‐area model catalysts that were based on colloidal Pd NPs and a hexagonally ordered mesoporous carbon support were prepared and the impact of various organic capping agents for the Pd NPs on their catalytic activity towards Suzuki coupling reactions was investigated. Colloidal Pd NPs (diameter: 3 nm) were synthesized with different organic capping agents, oleylamine (OA) and trioctylphosphine (TOP), and they were subsequently incorporated into the mesopores of CMK‐3 mesoporous carbon to yield OA‐Pd/CMK‐3 and TOP‐Pd/CMK‐3 nanocatalysts, respectively. The OA‐Pd/CMK‐3 catalyst was treated with acetic acid to generate a supported catalyst with surfactant‐free Pd NPs (OA‐Pd/CMK‐3‐A). Structural characterization revealed that the Pd NPs were uniformly dispersed throughout the mesopores of the CMK‐3 support and the particle size and crystallinity of the Pd NPs were preserved following the incorporation. All of the Pd/CMK‐3 nanocatalysts exhibited higher activity than commercial activated carbon supported Pd catalysts in Suzuki coupling reactions. The catalytic activities of the three Pd/CMK‐3 nanocatalysts were in the following order: OA‐Pd/CMK‐3‐A>OA‐Pd/CMK‐3>TOP‐Pd/CMK‐3. This result suggested that the presence and type of surfactants had a significant effect on the catalytic activity. The OA‐Pd/CMK‐3‐A catalyst also showed high activity for various substrates and good recycling ability in Suzuki coupling reactions.

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

Recent developments in the synthesis of SpellECuO 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.

Facile synthesis of Pd/Fe3O4/charcoal bifunctional catalysts with high metal loading for high product yields in Suzuki–Miyaura coupling reactions

In the present work, we synthesized magnetically separable Pd/Fe3O4/charcoal nanocatalysts by simple solid-state grinding of a mixture of salts and the simultaneous thermal decomposition of the salts. The highly loaded Pd nanoparticles (20 wt%) were well dispersed in the porous charcoal, with an average diameter of ∼5 nm and clean surfaces without any surfactant. Moreover, the simultaneously obtained Fe3O4 nanoparticles (10 wt%) had good superparamagnetic character, enabling quick separation of the catalyst from the products and re-dispersion in the reaction solution. The bifunctional catalyst showed a high product time yield with various substituted aryl halides and aryl boronic acids.

Au nanoparticles supported on magnetically separable Fe2O3–graphene oxide hybrid nanosheets for the catalytic reduction of 4-nitrophenol

A one-pot hydrothermal synthesis approach was developed to prepare FeSO4·(H2O)–graphene oxide (GO) nanosheets. Au nanoparticles were immobilized onto this support, giving Au/Fe2O3–GO nanocomposites. Fe2O3–GO supports showed high surface area and thermal stability. The Au/Fe2O3–GO and synthesized Au/Fe3O4 nanocomposites exhibited high catalytic activity and recyclability for the reduction of 4-nitrophenol.

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.

Optimized Dispersion and Stability of Hybrid Fe3O4/Pd Catalysts in Water for Suzuki Coupling Reactions: Impact of Organic Capping Agents

Pd nanoparticles were easily immobilized on Fe3O4 microspheres without any treatment such as functionalization with organic groups. The Fe3O4 microspheres were synthesized by using different capping agents, and the effect of the capping agents on the dispersion stability and catalytic activity of the Fe3O4/Pd composite for Suzuki coupling reactions in water were evaluated. The catalytic activity varied depending on the dispersion stability of Fe3O4/Pd catalysts in water. The Pd nanoparticles immobilized onto Fe3O4 microspheres capped with trisodium citrate showed strong dispersion stability in water over the reaction duration of seven days (at pH 7), high catalytic activity, and recyclability under mild conditions.

A new hybrid nanocatalyst based on Cu-doped Pd–Fe3O4 for tandem synthesis of 2-phenylbenzofurans

We report a one-pot synthesis of hybrid nanocomposites of Cu-doped Pd–Fe3O4via controlled thermal decomposition of Fe(CO)5 and reduction of Pd(OAc)2 and Cu(acac)2. Sodium oleate, used as a capping agent, affected both the morphologies and surface areas of the Cu-doped Pd–Fe3O4 nanocomposites. To the best of our knowledge, these magnetically recyclable hybrid nanocomposites are a new class of nanocatalysts, and the tandem synthesis of 2-phenylbenzofuran from 2-iodophenol with phenylpropiolic acid catalyzed by heterogeneous nanocatalysts has not been reported in the literature. Moreover, Cu-doped Pd–Fe3O4 nanocatalysts are superior to previously reported catalysts for this tandem reaction.

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.

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–MnOx 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–MnOx and dendritic Pt–MnOx 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–MnOx NPs were synthesized through the assembly of small seed NPs. On the other hand, dumbbell-like Pt–Fe3O4–MnOx 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–MnOx 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.