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 phot oelectron spectroscopy (XPS), thermally programmed desorption spectros copy (TPD) and workfunction measurements. The amount of K was varied b etween 0.1 ML and several monolayers, and the CO2 exposures were in th e 0.1-10 1, range. Although CO2 does not react with a clean Cu(110) su rface, several reaction channels open in the presence of the alkali me tal depending on the coverage. Different CO2 states and dissociated st ates can be assigned on the basis of energy positions and peak intensi ties of C(1s) and O(1s) core lines. Both physisorbed CO2 and a chemiso rbed anion, CO2-, were observed at 110 K. The effects of heating were followed with SRS. The chemisorbed CO2- anions react according to 2 CO 2- --> CO32- + CO(a) with CO desorbing at 200 K. Carbonate is formed a t all K coverages. The presence of CO2 on the surface stabilizes the a lkali metal as demonstrated by the use of selected state thermal desor ption. Decomposition of the carbonate occurs in the temperature range 450-550 K due to the reaction CO3 --> CO2 + O. A comparison is made wi th published data on CO2 adsorption on alkali-modified transition meta l surfaces with the conclusion that the adsorption characteristics and reactions are similar. It is demonstrated that a photon-induced react ion takes place, involving conversion of a physisorbed CO2 state to a negatively charged, chemisorbed state. The cross section was determine d to be 10(7) barn.