Homogeneous alloy nanoparticles as excellent catalysts. Spherical polyelectrolyte brushes can be used to generate Au-Pt alloy nanoparticles (see figure) that exhibit properties widely differing from the properties of the respective bulk alloys. The alloy nanoparticles are shown to be homogeneous solid solutions. Moreover, they are effective catalysts for the selective oxidation of alcohols to aldehydes and ketones.