CO oxidation on the IB group metals [Cu(111), Ag(111), and Au(111)] and corresponding metal oxides [Cu2O(100), Ag2O(100), and Au2O(100)] has been studied by means of density functional theory calculations with the aim to shed light on the reaction mechanism and catalytic activity of metals and metal oxides. The calculated results show that 1) the molecular oxygen mechanism is favored on Ag(111) and Au(111), but the atomic oxygen mechanism is favored on Cu(111); 2) the metal-terminated metal oxide shows very low activity for CO oxidation; 3) the lattice oxygen can react either with gas phase CO or the absorbed CO molecule on oxygen-terminated metal oxides; and 4) the reaction barrier for CO oxidation follows the order of M2O(100)–O
