| Studies of the water-gas shift (WGS) reaction, H{dollar}sb2{dollar}O + CO {dollar}to{dollar} CO{dollar}sb2{dollar} + H{dollar}sb2{dollar}, and its elementary steps over a low index face of copper (Cu(110)) and over cesium-promoted copper (Cs/Cu(110)) are presented. The experiments were performed on an apparatus that could interface medium pressure kinetic measurements with ultra-high vacuum surface analysis.; From the study of the gross kinetics of the WGS and of elementary steps on clean Cu(110), a mechanism was deduced. In this 'surface redox' mechanism, H{dollar}sb2{dollar}O is first dissociated completely to adsorbed hydrogen and adsorbed oxygen, and then the adsorbed oxygen is titrated by CO. The rate-determining step on clean Cu(110) was determined to be the initial dissociation of water to adsorbed hydrogen and adsorbed hydroxyl, OH{dollar}sb{lcub}rm a{rcub}{dollar}.; The addition of an alkali metal, Cs, to the Cu(110) surface increases the rate of the WGS reaction. The kinetics of the WGS reaction change, indicating a different rate determining step from clean Cu(110). In addition, a cesium-stabilized carbonate, Cs{dollar}cdot{dollar}CO{dollar}sb{lcub}rm 3,a{rcub}{dollar}, was discovered that does not form on the clean Cu(110) surface. From analysis of the elementary steps of WGS on Cs/Cu(110), this stable intermediate was determined to form from the CO{dollar}sb2{dollar} product and cesium-stabilized oxygen, Cs{dollar}cdot{dollar}O{dollar}sb{lcub}rm a{rcub}{dollar}. The rate of WGS on Cs-promoted Cu(110) is controlled by the competition for Cs{dollar}cdot{dollar}O{dollar}sb{lcub}rm a{rcub}{dollar} among CO, H{dollar}sb2{dollar}O, and CO{dollar}sb2{dollar}.; Among the elementary step reactions, the dissociative adsorption of hydrogen on Cu(110), H{dollar}sb2 to{dollar} 2H{dollar}sb{lcub}rm a{rcub}{dollar}, has been the most controversial. By indirect methods, the activation energy for this reaction was found to be 14.3 {dollar}pm{dollar} 1.4 kcal/mol. Dynamic modelling of the reaction conditions qualitatively showed that the translational energy of H{dollar}sb2{dollar} gas molecules was responsible for overcoming the activation barrier at {dollar}sim{dollar}600 K. |
