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 anal yzed 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 syn thetic pathway to the colloids and the type of reducing agent on the c atalytic activity of the colloids was found. The lowest activity was o bserved for N2H4 . H2O reduction which is related to a morphology wher e only a small number of noble-metal colloids is embedded in the micel le core. The highest activity was obtained for the super-hydride reduc tion where the data suggest the existence of many metal clusters per m icelle. The bimetallic Au/Pd colloids with metal ratios 1/5, 1/4, and 1/3 show the highest activity in hydrogenation of cyclohexene to cyclo hexane. The Pd monometallic and Au/Pd bimetallic colloids are also rat her selective catalysts (both in the homogeneous and a heterogeneous m odification), as shown by the hydrogenation of 1,3-cyclooctadiene and 1,3-cyclohexadiene to the corresponding cycloalkenes.