1 research outputs found
Selective Catalytic Ammonia Oxidation to Nitrogen by Atomic Oxygen Species on Ag(111)
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 (O<sub>a</sub>) 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 (O<sub>ox</sub>) 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 N<sub>2</sub> along with
minor amounts of NO and N<sub>2</sub>O. Higher coverage O/Ag(111)
surfaces, whose structure was tentatively assigned to a bulklike amorphous
silver oxide (O<sub>bulk</sub>), showed high selectivity toward N<sub>2</sub>O formation (rather than N<sub>2</sub>) 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 NH<sub>3</sub> 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 NH<sub>3</sub> to N<sub>2</sub> under well-defined experimental conditions
without generating significant quantities of environmentally toxic
species such as NO<sub>2</sub>, NO, or N<sub>2</sub>O