Investigating active site of gold nanoparticle Au55(PPh3)12Cl6 in selective oxidation.

We present an ab initio investigation of structural, electronic, catalytic, and selective properties of the ligand-covered gold nanoparticle Au55(PPh3)12Cl6 and associated model clusters. The catalytic activity of the Au55(PPh3)12Cl6 nanoparticle in the presence of O2 stems from a combined effect of triphenylphosphine ligands and surface structure of the "magic-number" quasi-icosahedral Au55 core, which entails numerous ligand-encompassed triangle Au6 faces as the active sites. Under the Eley-Rideal mechanism, the "triangle-socket" active site not only can accommodate one pre-adsorbed O2 (which is subsequently activated to the superoxo species) with one styrene molecule at a time but also can provide spatial confinement which favors the formation of an oxametallacycle intermediate that leads to unique selectivity in styrene oxidation.