Surface behaviour of NCO species on Rh(111) and polycrystalline Rh surfaces

Abstract

The adsorption and surface dissociation of HNCO on Rh surfaces has been investigated by Auger electron, electron energy loss and thermal desorption spectroscopy.Following the adsorption of HNCO on clean Rh(ll1) and Rh foil at 100 K three adsorbed states can be distinguished by thermal desorption measurements:(i) physisorbed HNCO desorbing at 130 K, (ii) chemisorbed HNCO desorbing at 200 K, and (iii) dissociatively adsorbed HNCO decomposing to various products at higher temperatures. These products are: H, ( Tp = 280 K), CO ( Tp = 450-480 K), N, (Tr = 670 and 790 K) and very small amount of NH, (L$ = 415 K). No desorption of N, was observed from Rh foil up to 900 K. This ws attrrbuted to the boron contamination, which segregated to the surface at higher temperature, and formed a oery stable surface species wrth N. The adsorption of HNCO at 100 K produced a very intense loss at 10.4 eV and a less intense one at 13.5 eV in the electron energy loss spectra in the electronic range. From the behaviour of these losses at higher temperature it was inferred that the dissociation of adsorbed NC0 species to adsorbed N and CO begins to an appreciable extent above 150 K, and that the dissociation is complete at 360-380 K.