NH_3 adsorption and decomposition on lr(110):A combined temperature programmed desorption and high resolution fast x-ray photoelectron spectroscopy study

摘要

The adsorption and decomposition of NH3 on Ir(ll0) has been studied in the temperature range from 80 K to 700 K.By using high-energy resolution x-ray photoelectron spectroscopy it is possible to distinguish chemically different surface species.At low temperature a NH_3 multilayer,which desorbs at approx 110 K,was observed.The second layer of NH_3 molecules desorbs around 140 K,in a separate desorption peak.Chemisorbed NH_3 desorbs in steps from the surface and several desorption peaks are observed between 200 and 400 K.A part of the NH_(3ad) decomposes into NH_(ad) between 225 and 300 K.NH_(ad) decomposes into N_(ad) between 400 K and 500 K and the hydrogen released in this process immediately desorbs.N2 desorption takes place between 500 and 700 K via N_(ad) combination.The steady state decomposition reaction of NH_3 starts at 500 K.The maximum reaction rate is observed between 540 K and 610 K.A model is presented to explain the occurrence of a maximum in the reaction rate.Hydrogenation of N_(ad) below 400 K results in NH_(ad).No NH_(2ad) or NH_(3ad)/NH_3 were observed.The hydrogenation of NH_(ad) only takes place above 400 K.On the basis of the experimental findings an energy scheme is presented to account for the observations.