Role of the nanoscale in catalytic CO oxidation by supported Au and Pt nanostructures

Experiments have found that the catalytic activity of Au increases sharply for supported nanoparticles smaller than 5 nm, while Pt exhibits the opposite behavior. Several authors, seeking to explain the nanoscale Au activity, reached conflicting conclusions, attributing it to different nanoscale features or to a particular bilayer structure that is independent of size. Here, we report an extensive theoretical study of a large ensemble of TiO₂-supported Au and Pt nanoparticles and show that several nanoscale features collectively result in the observed contrasting behavior. Low coordination is accompanied by bond weakening in Au and strengthening in Pt, while perimeter sites are active only for Au. Though there are orbital-occupancy differences for catalytically active and inactive configurations, there is insignificant variation in physical-charge transfer. Finally, we report atomically resolved Z-contrast images that confirm bond weakening in catalytically active TiO₂-supported Au nanoparticles.