Reactions on alkali-modified low-index stepped copper surfaces

Interest in CO, CO2 and H adsorption on alkali-promoted Cu surfaces stems f rom the promoting role of alkali metals in heterogeneous catalysis. Adsorpt ion 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 s trong consequences for the adsorption and reactive properties of the Cu sur faces. Another important factor for the reaction yields is the corrugation of the surface. The influence of these two parameters, the alkali metal cov erage and the corrugation, on the dissociation of CO and the reactions betw een low-molecular gases like H, CO and CO2 has been investigated on a serie s of low-index and stepped Cu surfaces. Particularly the synthesis of forma te HCOO- from coadsorption of H and CO2 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 de monstrated in this report that CO dissociates on the potassium-modified ste pped 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 --> CO2 + C and reaction with oxygen. Adsorption o f atomic hydrogen in the presence of K gives rise to two H-Is-induced state s in the valence band. The influence of temperature on the binding energies and the population of these states have been studied. Formate is synthesiz ed when the alkali/Cu surface, precovered with hydrogen, is exposed to CO2. (C) 2001 Elsevier Science Ltd. All rights reserved.