Structure-function relationships in dendrimer-encapsulated metal nanoparticles

The synthesis, characterization and structure-function relationships of mono- and bimetallic dendrimerencapsulated nanoparticles (DENs) are described. Control over the factors influencing the structure of bimetallic DENs has been attained for PdAu and AuAg systems. The bimetallic DENs are characterized by UV-vis, HRTEM, and single-particle energy dispersive x-ray spectroscopy (EDS). In addition, we use catalysis and selective extraction to chemically probe the surface structure. The fabrication of TiO2-supported Pd, Au and PdAu nanocomposites from DEN precursors is shown to be a viable route for the synthesis of catalytically active, reasonably monodisperse heterogeneous catalysts. Using the dendrimer-templating synthesis, tight control over the size of 1- 2 nm Pd DEN catalysts has led to the observation of a particle-size effect for the hydrogenation of allyl alcohol. We have proposed that for particles with diameters between 1.5? 1.9 nm the reaction occurs preferentially on the exposed face atoms.