Ligand-capped metal nanoparticles are considered as semi-heterogeneous catalysts that can be easily separated from products and other reaction medium. In addition, the high solubility of metal nanoparticles and the presence of ligands around the catalytic metal nanoparticle core can provide the higher catalytic efficiency and/or selectivity. Recently, our group discovered a synthetic method utilizing Bunte salts to generate catalytically active Pd nanoparticles capped with a low density of alkanethiolate ligands. This presentation focuses on the examination of various factors in the synthetic process of thiolate ligand-capped Pd nanoparticles (LcPdNP) that control the particle core size and the surface ligand density and their effects on the catalytic property of various LcPdNP catalysts. Factors which are manipulated include the molar equivalencies of sodium S-dodecylthiosulfate (capping ligand), tetra-n-octylammonium bromide (surfactant/phase transfer reagent), and sodium borohydride (reducing agent) and reaction temperature. In general, the results show that an increase in reaction temperature and a decrease in the concentration of tetra-n-octylammonium bromide result in a higher thiolate ligand density and smaller average particle size, while a decrease in the concentration of Bunte salts results in a lower surface ligand density and an increase in the average particle size. The amount of reducing agent, sodium borohydride, is also found to influence the size of Pd nanoparticles, producing particles with a smaller core with an increased borohydride concentration.  The catalysis studies show that the controlling the particle size and the surface ligand density of LcPdNP leads to the optimization of catalytic activity and selectivity for various organic transformations including the isomerization of allyl alcohols, tandem semi-hydrogenation and isomerization of propargyl alcohols, microwave-assisted isomerization of terminal alkenes, and hydrogenation of 4-nitrophenol. Water-soluble LcPdNP are also synthesized and their catalytic properties are studied for heterogeneous and two-phase catalysis reactions.

Regulating catalytic activity and selectivity of thiolate ligand-capped palladium nanoparticles

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.