Oxidation of CO by molecular oxygen on a Ag(1 1 0) surface studied by scanning tunneling microscopy

The oxidation of CO by O2 molecularly adsorbed on a Ag(1 1 0) surface was investigated by scanning tunneling microscopy in the temperature range between 60 and 110 K. At the lowest temperatures, CO remains weakly bound at Ag(1 1 0). Striped CO superstructures running along the [0 0 1] direction can be observed at intermediate coverages, indicating weak anisotropic interactions between the molecules. Upon exposing the oxygen precovered surface to CO at T≲90 K, O2 molecules either react off or (CO ⋯ O2)ad complexes evolve, signaling CO accumulation on the surface and attractive intermolecular interactions. At T≳90 K, adsorbed O2-molecules are highly mobile and CO molecules do not accumulate on the surface. Oxidation readily takes place upon CO exposure, whereby single oxygen atoms were identified as an intermediate product, which could be further titrated with CO molecules.