Oxygen chemisorption,surface oxidation,and the oxidation of carbon monoxide on cobalt (0001)

Oxygen chemisorbs on clean Co(0001) at 300 K with an initial sticking probability of ~0.3. The chemisorbed overlayer (which is very reactive towards CO) readily undergoes conversion to cobalt oxide, even at room temperature. This transformation is accelerated at higher temperatures, and the oxygen uptake rate falls as CoO growth proceeds. At a certain point, however, the uptake rate rises sharply, and this behaviour is ascribed to nucleation and growth ofCo₃O₄. This interpretation is consistent with the available Δφ, Auger, LEED, and reactivity data. Thus Δφ changes sign as lattice penetration by the ad sorbed oxygen takes place, and this is accompanied by a shift and broadening of the O(KLL) Auger signal. LEED indicates the epitaxial growth firstly of CoO(111) and then, at higher oxygen exposures, of Co₃O₄(111). At 300 K CO rapidly reduces the Co₃O₄ surface back to CoO, and the oxidation/reduction behaviour by O₂/CO appears to be completely reversible. Steady-state measurements yield a value of 19 ± 7 kJ mol^?1 for the activation energy to CO₂ production from CO + O₂. Earlier photoelectron spectroscopic studies by other authors are considered in the light of these results.