Reactions on alkali-modified low-index stepped copper surfaces

Abstract

Interest in CO, CO 2 and H adsorption on alkali-promoted Cu surfaces stems from the promoting role of alkali metals in heterogeneous catalysis. Adsorption of an alkali metal on a Cu surface causes a substantial decrease in the work function. The change in the electronic structure of the surface has strong consequences for the adsorption and reactive properties of the Cu surfaces. Another important factor for the reaction yields is the corrugation of the surface. The influence of these two parameters, the alkali metal coverage and the corrugation, on the dissociation of CO and the reactions between low-molecular gases like H, CO and CO 2 has been investigated on a series of low-index and stepped Cu surfaces. Particularly the synthesis of formate HCOO − from coadsorption of H and CO 2 has been studied. The experimental evidence for these findings is synchrotron radiation based measurements of valence band energy distributions, and work function measurements. It is demonstrated in this report that CO dissociates on the potassium-modified stepped surface, Cu(1 1 2), at 125 K. The dissociation process is conditioned by the presence of steps and the alkali metal coverage. Carbonate is formed via the process CO + CO →CO 2 + C and reaction with oxygen. Adsorption of atomic hydrogen in the presence of K gives rise to two H-1s-induced states in the valence band. The influence of temperature on the binding energies and the population of these states have been studied. Formate is synthesized when the alkali/Cu surface, precovered with hydrogen, is exposed to CO 2.