CO adsorption site preference on platinum : charge Is the essence

The adsorption of CO on transition-metal surfaces is a key step incatalysis and a reference system for surface science and computational catalysis.Here, the change in CO site preference with coverage, from top to bridge andback to top, is analyzed using charge transfer and chemical bonding. The relativestability of top and bridge sites is related to the variation in the surface platinumcharge with CO coverage. Both the Pt−C σ* (Pauli repulsion) and the C−O π*(back-donation) occupancies increase with platinum charge; however,destabilizing Pauli repulsion dominates over stabilizing back-donation, andadsorption weakens with increasing surface charge. CO at the top sites is moresensitive to Pauli repulsion, leading to a change in site preference from top tobridge with increasing platinum charge and, consequently, with increasing COcoverage. The higher back-donation at the bridge sites eventually switches thesite preference back to top near monolayer coverage.The adsorption of CO on transition-metal surfaces is a key step incatalysis and a reference system for surface science and computational catalysis.Here, the change in CO site preference with coverage, from top to bridge andback to top, is analyzed using charge transfer and chemical bonding. The relativestability of top and bridge sites is related to the variation in the surface platinumcharge with CO coverage. Both the Pt−C σ* (Pauli repulsion) and the C−O π*(back-donation) occupancies increase with platinum charge; however,destabilizing Pauli repulsion dominates over stabilizing back-donation, andadsorption weakens with increasing surface charge. CO at the top sites is moresensitive to Pauli repulsion, leading to a change in site preference from top tobridge with increasing platinum charge and, consequently, with increasing COcoverage. The higher back-donation at the bridge sites eventually switches thesite preference back to top near monolayer coverage.A