OXYGEN INDUCED ADSORPTION AND REACTION OF H-2, H2O, CO AND CO2 ON SINGLE-CRYSTAL AG(110)
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The adsorption and reaction of H2, H2O, CO, and CO2 were examined on clean and oxygen-dosed Ag(110) surfaces. Limited adsorption with no reaction of these species was observed at surface temperatures down to 160 K on the clean surface. Although no adsorption of H2 was observed on the oxygen-dosed surface, the adsorption and reaction of the remaining species were strongly affected by the presence of oxygen. The sticking probability and desorption rate measurements for oxygen were in reasonable agreement with the results of other workers. For sequential exposure of the surface to 16O2 and 18O2, random isotopic mixing of the O2 desorbed from the surface was observed, indicating appreciable mobility within the adlayer. At 160 K ten H2O molecules could be adsorbed for each oxygen atom initially present on the surface; experiments with isotopically labelled oxygen revealed that complete isotopic mixing of oxygen between adsorbed H2O and the surface had occurred suggesting the formation of adsorbed OH groups. During the adsorption of CO on the oxygen-dosed Ag(110) surface, CO was rapidly oxidized via a chemisorbed state to CO2. The negative apparent activation energy for this process is shown to be the difference between the activation energies for the reaction step and for the desorption of CO from the surface. In the presence of surface oxygen CO2 was adsorbed to form a surface carbonate species which decomposed at 485 K to yield CO2 and O(a). 1980.
