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| - Effect of Coadsorbed Oxygen on the Chemistry of Ammonia over Ni(110)Single-Crystal Surfaces
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| - The surface chemistry of ammonia coadsorbed with atomic oxygen on Ni(110) single-crystal surfaces wasstudied by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Atintermediate oxygen coverages, direct ammonia adsorption on nickel sites is suppressed, but a new high-temperature reaction regime is generated. Desorption of ammonia from rehydrogenation of NHx surfacefragments (identified by XPS) takes place around 400 K, concurrently with the production of water andmolecular hydrogen. Experiments with deuterium labeling indicated extensive isotope scrambling and hydrogentransfer from nitrogen- to oxygen-containing surface intermediates. The optimum yields seen for this 400 Kstate at intermediate oxygen coverages strongly suggest the direct interaction of the adsorbed ammonia withoxygen atoms at the end of the −Ni−O− rows that form upon reconstruction of the surface. Hydrogen transferbetween ammonia and oxygen appears to take place directly via hydrogen bonding, and to be reversible butbiased toward water formation. An equilibrium is reached between the produced water and the reacting surfaceoxygen and hydrogen.
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