A COMBINED IN-SITU PM-RAIRS AND KINETIC-STUDY OF SINGLE-CRYSTAL COBALT CATALYSTS UNDER SYNTHESIS GAS AT PRESSURES UP TO 300-MBAR

The coadsorption behavior of CO and hydrogen on Co(0001) during exposu re to mixtures of H-2 and CO at pressures up to 300 mbar and temperatu res between 298 and 490 K has been studied by in-situ polarization mod ulation reflection absorption infrared spectroscopy (PM-RAIRS). At 490 K it is shown that adsorbed CO molecules attached to cobalt atoms at step edges (''defect sites'') disappear. We explain this observation i n terms of hydrocarbon formation at defect sites, which blocks the ads orption of CO at these positions. To support this explanation, both ex -situ X-ray photoelectron spectroscopy measurements and kinetic measur ements have been performed. The kinetic measurements provide direct ev idence for a link between the number of defect sites at the surface an d the total Fischer-Tropsch activity.