Adsorption and decomposition of HNCO on Cu(111) surface studied by Auger electron, electron energy loss and thermal desorption spectroscopy

Abstract

No detectable adsorbed species were observed after exposure of HNCO to a clean Cu(ll1) surface at 300 K. The presence of adsorbed oxygen, however, exerted a dramatic influence on the adsorptive properties of this surface and caused the dissociative adsorption of HNCO with concomitant release of water. The adsorption of HNCO at 300 K produced two new strong losses at 10.4 and 13.5 eV in electron energy loss spectra, which were not observed during the adsorption of either CO or atomic N. These loses can be attributed to surface NC0 on Cu( 111). The surface isocyanate was stable up to 400 K. The decomposition in the adsorbed phase began with the evolution of COz. The desorption of nitrogen started at 700 K. Above 800 K, the formation of CzNz was observed. The characteristics of the CO, formation and the ratios of the products sensitively depended on the amount of preadsorbed oxygen. No HNCO was desorbed as such, and neither NC0 nor (NCO)? were detected during the desorption. From the comparison of adsorption and desorption behaviours of HNCO, N, CO and CO2 on copper surfaces it was concluded that NC0 exists as such on a Cu(ll1) surface at 300 K. The interaction of HNCO with oxygen covered Cu(ll1) surface and the reactions of surface NC0 with adsorbed oxygen are discussed in detail.