Mechanistic pathways for oxygen removal on Pt-doped Co(111) in the Fischer-Tropsch reaction

Abstract

Water is a significant by-product in the cobalt-based Fischer-Tropsch synthesis as the dissociation of CO on metallic cobalt must eventually lead to the formation of water. Hence, the removal of oxygen in the form of water, could potentially limit the intrinsic activity on a cobalt-based catalyst. In this study, potential mechanisms for the removal of strongly bound surface oxygen by hydrogenation to water on fcc Co(111) and Pt doped fcc Co(111) surfaces are investigated using density functional theory and micro-kinetic modelling to probe the effect that of platinum promotion. We show that the formation of water proceeds primarily via disproportionation of adsorbed OH, 2 OH ↔ H2O + O, rather than the hydrogenation of surface hydoroxyl species, OH + H ↔ H2O, on both surfaces. Doping cobalt with platinum increases the rate of oxygen removal in the form of water by four orders of magnitude, by reducing the barrier of the hydrogenation of surface oxygen, O + H ↔ OH, by 0.48 eV.