Abstract
The interaction of CO with a Ni(111) surface alloyed with different amounts of iron is studied with ellipsometry and AES. For surfaces with an iron mole fraction of X Fe≤0.26 CO adsorbs only molecularly. The isosteric heat of adsorption is 106±5 kJ/mol and is independent of the CO coverage and X Fe. On surfaces with X Fe≥0.39 both dissociatively and molecularly adsorbed CO are observed. The carbon and oxygen coverages after CO dissociation are equal and increase with X Fe. On these surfaces with dissociatively adsorbed CO further reversible adsorption of molecular CO takes place. Small amounts of carbon and oxygen do not affect the isosteric heat of adsorption at low CO coverage. Because no dissociation of CO proceeds on surfaces with X Fe≤0.26, whereas on surfaces with X Fe≥0.39 it does, the dissociation requires an ensemble of iron atoms that has a minimum size of at least two atoms. CO does not cause segregation of iron to the surface.
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