(760d) Selective Oxidation Chemistry on Gold

The reactivity of atomic oxygen on Au(111) has been investigated employing molecular beam scattering and temperature programmed desorption (TPD) techniques under ultrahigh vacuum (UHV) conditions. We demonstrate that adsorbed O atoms (O_ad) facilitate NH_3,ad decomposition even though ammonia does not dissociate on the clean Au(111) surface. The selectivity of the catalytic oxidation of ammonia to N₂ or to NO on Au(111) is tunable by the amount of atomic oxygen pre-covering the surface. Both N₂ and NO are formed via simple recombination reactions (N_ad + N_ad and N_ad + O_ad). At low oxygen coverages (Θ_O < 0.5 ML), adsorbed ammonia is stripped to NH_x,ad which decomposes to form gaseous N₂.

We also present experimental and density functional theory (DFT) calculation results of formation and decomposition of the carbonate anion (CO₃ = CO₂ + O_ad) on atomic oxygen pre-covered Au(111). A reaction probability on the order of 10^-4 and an apparent activation energy of -0.15 eV are estimated for this reaction. The small values of reaction probability are likely part of the reason why an earlier study on Au(111) reported undetectable surface carbonate formation. Additionally, we have investigated partial oxidation of propanol on atomic oxygen covered Au(111). At reaction temperatures below 300 K, 1-propanol is oxidized to propaldehyde with 100% selectivity while acetone is the only products of 2-propanol partial oxidation. A small amount of CO₂ is formed at higher surface temperatures (i.e., above 300 K).