Preparation of Colloidal Transition Metals in Polymers by Reduction with Alcohols or Ethers

Colloidal dispersions of rhodium, palladium, osmium, iridium, and platinum are prepared by refluxing the methanol-water solutions of rhodium(III) chloride, palladium(II) chloride, osmium(VIII) oxide, sodium chloroiridate, and chloroplatinic acid, respectively, in the presence of poly(vinyl alcohol) as a protective colloid. The preparations of colloidal dispersions of rhodium are successful in the presence of vinyl polymer with polar group such as poly(vinyl alcohol), polyvinylpyrrolidone, or poly(methyl vinyl ether). Polyethyleneimine, gelatin, polyethylene glycol), and dextran are ineffective as the protective colloid. Water-soluble primary alcohols such as methanol and ethanol, water-soluble secondary alcohols such as 2-propanol, and water-soluble diethers such as 1,4-dioxane are available as reductants for preparation of the colloidal dispersion of rhodium. The average diameters of metal particles in the colloidal dispersions of palladium, rhodium, platinum, iridium, and osmium in poly(vinyl alcohol) are determined by electron microscopy to be 53, 40, 27, 14, and < 10 Å, respectively. The particle size distribution in each colloidal dispersion is sharp within 50 Å wide. The particles in the colloidal dispersions of both iridium and osmium are highly dispersed with no aggregation, while in the colloidal dispersions of rhodium, palladium, and platinum, there exist aggregates of 5-15, 5-30, and 100-200 particles, respectively. Colloidal dispersions of rhodium, palladium, osmium, and platinum are effective as catalysts for hydrogenation of cyclohexene at 30.0°C under atmospheric hydrogen pressure.