Abstract
Experiments have found that the catalytic activity of Au increases sharply for supported nanoparticles smaller than 5 nm, while Pt exhibits 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.
