Superoxide Formation on Isolated Cationic Gold Clusters

Gold nanoparticles are known to be highly versatile oxidation catalysts utilizing molecular oxygen as a feedstock, but the mechanism and species responsible for activating oxygen remain unclear. The reaction between unsupported cationic gold clusters and molecular oxygen has been investigated. The resulting complexes were characterized in the gas phase using IR spectroscopy. A strong red-shift in the observed v(O-O) stretching frequency indicates the formation of superoxo (O-2(-)) moieties. These moieties are seen to form spontaneously in systems, which upon electron transfer attain a closed shell within the spherical jellium model (Au-10(+) and Au-22(+)), whereas an oxygen induced self-promotion in the activation is observed for other systems (Au-4(+), Au-12(+), Au-21(+)).