Sequential carbon oxygen bond cleavage in chemisorption of CO2 on Fe(100)

Abstract

Adsorption and dissociation of CO2 on Fe(100) was studied using temperature programmed desorption, x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy-loss spectra (HREELS), and low-energy electron diffraction. CO2 adsorbs on Fe(100) at 110 K to form two distinct adsorbed species: a physisorbed, molecular CO2 species and chemisorbed, bent anionic CO−2 species. These two species were characterized by HREELS losses at 2258 cm−1 for the asymmetric mode of the molecular CO2 state and at 1634 and 1232 cm−1 for asymmetric and symmetric modes of anionic CO2− state. Two features in O(1s) XPS spectrum for CO2 were observed at 534.9 and 531.1 eV binding energy and were assigned to the physisorbed and chemisorbed species, respectively. UPS data also indicate that a fraction of the adsorbed CO2 molecules at 110 K are in a bent CO−2 configuration. The molecular CO2 was found to desorb at 162 K where as the anionic form remains on the surface to dissociate. The dissociation upon heating is shown to proceed through two sequential carbon–oxygen bond breaking events. Strongly chemisorbed CO is produced as an intermediate in the dissociation process.