Adsorption of CO 2 on clean and potassium-covered Pd(100) surfaces

Abstract

The adsorption of CO 2 on the clean and potassium-predosed Pd(100) surface is studied using Auger electron, electron energy loss (in the electronic range), and thermal desorption spectroscopies. Adsorption of CO 2 on a clean Pd(100) surface is weak and nondissociative. However, the preadsorbed potassium dramatically affected the adsorption behavior of CO 2 on Pd(100) and it caused significant changes in the electron energy loss spectrum of adsorbed CO 2. It increased (i) the amount of weakly adsorbed CO 2, (ii) the rate of CO 2 adsorption, and (iii) the binding energy of CO 2, and (iv) it induced the formation of new adsorption states and lowered the activation barrier for dissociation. The lowest potassium coverage where the dissociation of CO 2 was detected was θ K = 0.21. The peak temperatures for CO desorption were 624 and 693 K, which are significantly higher than those measured for the clean Pd(100) surface. The adsorption of CO 2 on potassiumdosed Pd leads to a work function increase of 2.20 eV at nearly monolayer of potassium. This indicates a substantial charge transfer from the potassium-dosed metal to an empty CO 2 πr ∗ orbital; as a result the bonding and the structure of adsorbed CO 2 are basically changed. In the interpretation of the data a direct interaction between preadsorbed K and CO 2 leading to the formation of carbonate and CO is also considered.