Transition metal nanoparticles protected by amphiphilic block copolymers as tailored catalyst systems

Abstract

Several stable palladium, platinum, silver, and gold colloids were prepared by reducing the corresponding metal precursors in the presence of protective amphiphilic block copolymers. Some palladium and platinum precursors with different hydrophobicities, namely palladium chloride PdCl₂, palladium acetate Pd(CH₃COO)₂, hexachloroplatinic acid H₂PtCl₆, and platinum acetylacetonate Pt(CH₃COCH = C(O-)CH₃)₂, have been used in order to investigate differences in their catalytic activity. The polymers investigated for their ability to stabilize such transition metal colloids were polystyrene-b-poly(ethylene oxide) and polystyrene-b-poly (methacrylic acid). The metal particle sizes and morphologies were determined by transmission electron microscopy and found to be in the nanometer range. The catalytic activity of the palladium and platinum colloids was tested by the hydrogenation of cyclohexene as a model reaction. The protected palladium and platinum nanoparticles were found to be catalytically active, and final conversions up to 100% cyclohexane could be obtained. Depending on the choice of polymer block types and lengths, the precursor type, and the reduction method, different nanoparticle morphologies and catalytic activities could be obtained. These novel catalytically active metal-polymer systems are thus promising candidates for the development of tailored catalyst systems.