Activation and Reactions of CO2 on a K-Promoted Au(111) Surface

The adsorption of potassium and CO2 and their interaction on a Au(111) surface have been studied using high-resolution electron energy loss spectroscopy, thermal desorption spectroscopy, work function measurements, and Auger electron spectroscopy. Potassium adsorbs in cationic form on Au(111) at low coverage, depolarizing to a neutral metallic state at high coverage. CO2 adsorbs only weakly on clean Au(111), desorbing with a T-p similar to 124 K. Its binding energy is greatly enhanced by the presence of potassium and led to the formation of a CO2- anion radical characterized by losses at 957, 1360, and 1620 cm(-1). An enhancement of a weakly held, unperturbed CO2 also occurred on a K-dosed Surface, which was attributed to the formation of an unstable cluster compound (CO2)(n)center dot CO2-. The surface concentration and the reactivity of the CO2- radical sensitively depend on the K coverage and on the state of potassium. At low K coverages, CO2- dissociated into CO(a) and O-(a)(-). At higher coverages, it disproportionated into stable CO3(a)- and CO(a)-; they decomposed and released only above 500 K. CO formed on a K-dosed surface gave vibration losses at 1940-1700 cm(-1) and was also stabilized by potassium.