Small platinum particles of colloidal size (5̃0 - 60 Å) are readily obtained by reducing K2PtCl4, entrapped in polymerized vesicles, by means of UV irradiation. These particles can be used in catalytic hydrogenation either directly in the vesicle (ethylene hydrogenation) or indirectly by depositing them on silica gel (cyclohexene hydrogenation). The activity of vesicle-entrapped platinum increases with decreasing particle size. The utilization of this catalyst is limited to reactants which can diffuse through the polymerized wall of the vesicle. This disadvantage is eliminated by destroying the vesicles prior to the deposition of the platinum particles on silica gel. In this case the catalytic activities are similar to those of other catalysts prepared by classical methods.
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