Impurity effects in the adsorption and dissociation of CO 2 on Rh

Abstract

The adsorption and dissociation of CO2 on Rh(111) and Rh foil surfaces have been studied in UHV using Auger electron, electron energy loss (in the electronic range) and thermal desorption spectroscopy. CO2 adsorbs weakly with a low sticking probability on clean Rh samples at 110 K. The adsorption is accompanied by the appearance of a loss feature at 14 eV. The adsorption of CO2 took place in two stages, with Tp = 244–233 K (α) and 170 K (β). Adsorption of 180 L CO2 at 3 × 10−7 Torr on clean Rh(111) at 300 K produced no observable changes in the LEEd, Auger electron, EEL or TD spectra and there was no indication of the dissociation of CO2 either. Similar results were obtained for a clean Rh foil. However, boron impurity segregated on the surface of Rh exerted a dramatic influence on the adsorptive properties of this surface and caused the dissociation of CO2 at 270–300 K. This was exhibited by the appearance of an intense loss in the EEL spectrum due to chemisorbed CO, by the buildup of surface oxygen and by the thermal desorption of CO at higher temperatures.