The adsorption of CO at high pressures (up to 120 Torr) on a hydrocarb
on-precovered Mo(100) surface is studied by reflection-absorption infr
ared spectroscopy (RAIRS). It is shown that CO adsorbs reversibly on t
he Mo(100) surface even in the presence of a thick (similar to C-8) ca
rbonaceous layer and forms a saturation coverage of about 20% of that
on clean Mo(100). Although CO is used as a probe molecule, this result
confirms that, under high pressure, the reactants still can adsorb on
the catalyst in spite of the presence of a thick carbonaceous layer f
ormed under the reaction conditions.