Catalysis of colloidal transition metal nanoparticles in aqueous medium

Different transition metal nanoparticles were prepared by using different stabilizers. Pt nanoparticles stabilized by polyacrylate and Au nanoparticles stabilized by citrate were used as catalysts in the electron-transfer reaction between thiosulfate and hexacyanoferrate(III) ions, from which initial rates and activation energies were determined. The catalytic activity and stability of Pt nanoparticles were compared with those of Au nanoparticles.; Pd nanoparticles stabilized by linear polymer, block copolymer, and dendrimers were used as catalysts in the C-C bond formation reactions such as Suzuki and Heck reactions in aqueous solution.; Pd nanoparticles stabilized by PVP were found to be efficient catalysts for some Suzuki coupling reactions between arylboronic acids and aryl halides in colloidal aqueous solution. The linear dependence of initial rate on the concentration of Pd catalyst suggests that the catalysis occur on the nanoparticle surface.; Pd nanoparticles prepared by the reduction of metal salts in the presence of three different stabilizers—dendrimers, block copolymer, and PVP—were used as catalysts in the Suzuki reactions in aqueous solution. The aim of this study is to investigate the effects of these stabilizers on the nanoparticle catalytic activity and stability and to determine how theses two properties change as different stabilizers are used. It was found that the nanoparticle stability was controlled by the type of stabilizer, reactant, and base used in the reaction system. Generally these two properties are anticorrelated, that is, the most stable is the least catalytically active.; A series of PVP-Pd nanoparticles with varying particle size were prepared by using the stepwise growth reaction. The particle size effect on the catalytic Suzuki reaction between phenylboronic acid and iodobenzene was investigated by using HPLC. The increase in catalytic activity with decreasing particle size suggests that the low coordination number vertex and edge atoms on the particle surface are active centers for the catalysis.; The initial rates of Pd-nanoparticle-catalyzed reaction of phenylboronic acid and iodobenzene were measured over a range of reactant and base concentrations. The kinetic data suggests that the catalytic mechanism include fast oxidative addition, rate-determining transmetalation, and fast reductive elimination. The activation energy was determined to be 103 ± 7 kJ/mol.