The coadsorption behavior of CO and hydrogen on Co(0001)
during exposure to mixtures of H2 and CO at
pressures up to 300 mbar and temperatures between 298 and 490 K has
been studied by in-situ polarization
modulation 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
in terms of hydrocarbon formation at defect sites, which blocks the
adsorption of CO at these positions. To
support this explanation, both ex-situ X-ray
photoelectron spectroscopy measurements and kinetic
measurements
have been performed. The kinetic measurements provide direct
evidence for a link between the number of
defect sites at the surface and the total Fischer−Tropsch
activity.
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