Palladium and platinum nanocatalysts protected by amphiphilic block copolymers

Abstract

Several palladium and platinum colloids stabilized by polystrene-b-poly(methacrylic acid) (PS-b-PMAA) and polystyrene-b-poly(ethylene oxide) (PS-b-PEO) in a polar medium were prepared by in situ reductions from various precursors. Micelle formation of these diblock copolymers, as well as the particle sizes, morphologies, and size distributions of the metal nanoparticles were investigated by transmission electron microscopy. The catalytic activities of the colloidal metal nanoparticles were qualitatively determined by the hydrogenation of cyclohexane as a model reaction. The activities thus observed for these polymer-metal systems were found to depend significantly on precursor type and preparation conditions. These differences could be due to several factors, such as (i) partial embedding of the nanocatalysts within the hydrophobic micelle cores, (ii) influences of the side products of the reducing agent, or of the metal precursor counterions, or (iii) changes in the block copolymer micelle diameters or morphologies.