Design of Colloidal and Supported Metal Nanoparticles: Their Synthesis, Characterization, and Catalytic Application

Fabrication of nanoparticle (NP)-based materials have attracted much attention in the field of catalysis, because their special properties lie between those of single metal species and bulks. In this review article, we highlight our recent progress in the development of promising NPs-based catalysts designed by precise architecture that enable efficient and selective chemical reactions and can be easily separated and recyclable. Firstly, novel strategies to fabricate well-controlled catalytically active metal NPs on solid supports are described. A single-site photocatalyst comprising tetrahedrally coordinated Ti-oxide moieties within a silica framework (Ti-MCM-41) enabled a high dispersion of metal NPs via the photo-excitation. Both the deposition of Pd and Au to form PdAu bimetallic NPs was also accomplished under UV-light irradiation. These bimetallic NPs showed an improvement in the catalytic efficiency of H2O2 formation. Based on pH-induced assembly-dispersion properties of Ag NPs stabilized with 3-mercaptopropionic acid (3-MPA), the deposition of Ag NPs on Al2O3 support was successfully attained by electrostatic attraction while keeping their inherent dispersion state. In the second topic, new multifunctional nanocomposites exhibiting magnetic properties and catalytic activities are presented. Magnetic NPs were encapsulated with silica layer containing isolated and tetrahedrally-coordinated Ti-oxide species, which offered simple and efficient catalyst systems for the selective liquid-phase oxidations. The FecorePtshell NPs stabilized by oleic acid and oleylamine was drastically improved by the formation of an inclusion complex with gamma-cyclodextrin (gamma-CD), which showed an enhanced catalytic activity in water rather than in organic solvents. Similarly, the FecorePtshell NPs were subsequently treated with 2,2'-bis(diphenylphosphino)-1,1'-binaphthene (BINAP) as chiral modifiers, which were shown to catalyze the asymmetric Suzuki-Miyaura coupling reaction. Hollow gamma-Fe2O3 nanoshperes with diameter of 400-500 nm have been synthesized by a simple templating method combined with subsequent thermal treatments and calcinations. It exhibited higher catalytic activity than its bulk counterparts and also showed a satisfactory selectivity compared to the nano-gamma-Fe2O3. The synthetic strategies described here are simple and general for practical catalyst design; thus allowing a strong protocol for creating various nanostructured catalysts.