ADSORPTION AND REACTIVITY OF CO2 ON THE K/CU(110) INTERFACE AND THE EFFECT OF PHOTON IRRADIATION

Adsorption and reactions of CO2 on Cu(110) with preadsorbed potassium were studied with synchrotron radiation spectroscopy (SRS), X-ray photoelectron spectroscopy (XPS), thermally programmed desorption spectroscopy (TPD) and workfunction measurements. The amount of K was varied between 0.1 ML and several monolayers, and the CO2 exposures were in the 0.1-10 1, range. Although CO2 does not react with a clean Cu(110) surface, several reaction channels open in the presence of the alkali metal depending on the coverage. Different CO2 states and dissociated states can be assigned on the basis of energy positions and peak intensities of C(1s) and O(1s) core lines. Both physisorbed CO2 and a chemisorbed anion, CO2-, were observed at 110 K. The effects of heating were followed with SRS. The chemisorbed CO2- anions react according to 2 CO2- --> CO32- + CO(a) with CO desorbing at 200 K. Carbonate is formed at all K coverages. The presence of CO2 on the surface stabilizes the alkali metal as demonstrated by the use of selected state thermal desorption. Decomposition of the carbonate occurs in the temperature range 450-550 K due to the reaction CO3 --> CO2 + O. A comparison is made with published data on CO2 adsorption on alkali-modified transition metal surfaces with the conclusion that the adsorption characteristics and reactions are similar. It is demonstrated that a photon-induced reaction takes place, involving conversion of a physisorbed CO2 state to a negatively charged, chemisorbed state. The cross section was determined to be 10(7) barn.