By application of reactive thermal desorption spectroscopy and the sur
face titration technique we found strong evidence for a direct reactio
n of CO with molecularly adsorbed oxygen on a Ag(110) surface forming
CO2 as the product. The reaction takes place between 100 and 130 K, cl
early below the dissociation temperature of the oxygen molecule, and f
ollows the Langmuir-Hinshelwood scheme.