Preparation of Noble-Metal Colloids in Block Copolymer Micelles and Their Catalytic Properties in Hydrogenation

Monometallic and bimetallic colloids were prepared in micelles of the block copolymer polystyrene- b -poly-4-vinylpyridine in toluene and analyzed by electron microscopy and various techniques of X-ray analysis. These metal colloids were studied in hydrogenation of cyclohexene, 1,3-cyclooctadiene, and 1,3-cyclohexadiene. A strong influence of the synthetic pathway to the colloids and the type of reducing agent on the catalytic activity of the colloids was found. The lowest activity was observed for N 2 H 4 ·H 2 O reduction which is related to a morphology where only a small number of noble-metal colloids is embedded in the micelle core. The highest activity was obtained for the super-hydride reduction where the data suggest the existence of many metal clusters per micelle. The bimetallic Au/Pd colloids with metal ratios 1/5, 1/4, and 1/3 show the highest activity in hydrogenation of cyclohexene to cyclohexane. The Pd monometallic and Au/Pd bimetallic colloids are also rather selective catalysts (both in the homogeneous and a heterogeneous modification), as shown by the hydrogenation of 1,3-cyclooctadiene and 1,3-cyclohexadiene to the corresponding cycloalkenes.