| AVS 54th International Symposium | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Reactions on Metal Surfaces |
| Presenter: | J.L. Gong, University of Texas at Austin |
| Authors: | J.L. Gong, University of Texas at Austin R.A. Ojifinni, University of Texas at Austin J.M. White, University of Texas at Austin C.B. Mullins, University of Texas at Austin |
| Correspondent: | Click to Email |
The reactivity of atomic oxygen on Au(111) has been investigated by employing molecular beam scattering and temperature programmed desorption (TPD) techniques under ultrahigh vacuum (UHV) conditions.We demonstrate that ammonia does not dissociate on the clean Au(111) surface but adsorbed O atoms, Oad, facilitate NH3,ad decomposition. The selectivity of the catalytic oxidation of ammonia to N2 or to NO on Au(111) is tunable by the amount of atomic oxygen precovering the surface. Both N2 and NO are likely formed via simple recombination reactions (Nad + Nad and Nad + Oad). At low oxygen coverages (θO < 0.5 ML) (1 ML of oxygen is defined as 1.387 x 1015 atoms/cm2 and refers to a single atomic layer of close-packed gold), adsorbed ammonia is stripped to NHx ad which decomposes to form gaseous N2. At high Oad coverages, NO is formed in a surface reaction between Nad and Oad, but most surface N species involved recombine to form N2 which desorbs with a peak at ~ 460 K. Higher yields of N2 can be obtained if the O2/NH3 mix is kept NH3 rich. We also present results of low-temperature CO oxidation and the role of moisture on an atomic oxygen covered Au(111) surface. The effect of atomic oxygen precoverage on CO oxidation was examined at sample temperatures as low as 77 K. Prompt CO2 production was observed when the CO beam impinges on the sample followed by a rapid decay of CO2 production in all cases. At oxygen precoverages above 0.5 ML, the initial CO2 production decreases with increasing oxygen precoverage primarily due to the decrease in CO uptake. CO oxidation at 77 K goes through a precursor mediated reaction mechanism, where CO is in a precursor or trapped state and oxygen atoms are in a chemisorbed state. The role of adsorbed water was studied by using isotopically labeled water [H218O] to distinguish the oxygen species from that used in oxygen atom exposures [16O]. Evidence is presented that shows activated water or OH groups formed from water can directly participate in oxidizing CO on an atomic oxygen covered Au(111) surface.