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      Selective catalytic ammonia oxidation to nitrogen by atomic oxygen species on Ag (111)

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      Author
      Karatok, M.
      Vovk, E. I.
      Koc, A. V.
      Ozensoy, E.
      Date
      2017
      Source Title
      Journal of Physical Chemistry C
      Print ISSN
      1932-7447
      Publisher
      American Chemical Society
      Volume
      121
      Issue
      41
      Pages
      22985 - 22994
      Language
      English
      Type
      Article
      Item Usage Stats
      125
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      130
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      Abstract
      Ammonia-selective catalytic oxidation was studied on the planar Ag(111) single-crystal model catalyst surface under ultra-high-vacuum (UHV) conditions. A variety of oxygen species were prepared via ozone decomposition on pristine Ag(111). Surface coverages of oxygen species were quantified by temperature-programmed desorption (TPD) and X-ray photoemission spectroscopy techniques. Exposure of ozone on Ag(111) at 140 K led to a surface atomic oxygen (Oa) overlayer. Low-energy electron diffraction experiments revealed that annealing of this atomic oxygen-covered Ag(111) surface at 473 K in UHV resulted in the formation of ordered oxide surfaces (Oox) with p(5×1) or c(4×8) surface structures. Ammonia interactions with O/Ag(111) surfaces monitored by temperature-programmed reaction spectroscopy indicated that disordered surface atomic oxygen selectively catalyzed N-H bond cleavage, yielding mostly N2 along with minor amounts of NO and N2O. Higher coverage O/Ag(111) surfaces, whose structure was tentatively assigned to a bulklike amorphous silver oxide (Obulk), showed high selectivity toward N2O formation (rather than N2) due to its augmented oxygen density. In contrast, ordered surface oxide overlayers on Ag(111) (where the order was achieved by annealing the oxygen adlayer to 473 K) showed only very limited reactivity toward ammonia. The nature of the adsorbed NH3 species on a clean Ag(111) surface and its desorption characteristics were also investigated via infrared reflection absorption spectroscopy and TPD techniques. Current findings demonstrate that the Ag(111) surface can selectively oxidize NH3 to N2 under well-defined experimental conditions without generating significant quantities of environmentally toxic species such as NO2, NO, or N2O.
      Keywords
      Absorption spectroscopy
      Ammonia
      Atoms
      Catalytic oxidation
      Crystal atomic structure
      Desorption
      Electrons
      Oxidation
      Oxygen
      Ozone
      Photoelectron spectroscopy
      Silver compounds
      Silver oxides
      Single crystals
      Temperature programmed desorption
      Ultrahigh vacuum
      Desorption characteristics
      Disordered surfaces
      Experimental conditions
      Infrared reflection absorption spectroscopy
      Ozone decomposition
      Selective catalytic oxidation
      Temperature-programmed reaction spectroscopies
      X ray photoemission spectroscopy
      Silver
      Permalink
      http://hdl.handle.net/11693/37294
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/acs.jpcc.7b08291
      Collections
      • Department of Chemistry 594
      • Institute of Materials Science and Nanotechnology (UNAM) 1775
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