CO interaction with Fe(100): Effects of carbon and oxygen adlayers on co adsorption isotherms

Abstract

The interaction of CO with clean Fe(100) at 300 K is shown to occur in two distinct stages. namely: (i) Dissociation of CO, leading to a carbon and oxygen coverage of approximately 0.25 monolayer respectively as indicated by AES and LEED, and (ii) reversible molecular CO adsorption which has been studied with ellipsometry. The isosteric heat of adsorption is dependent on the CO coverage and equals 100 ± 5 kJ mol at zero coverage. CO adsorption isotherms were recorded on a carbon covered Fe(100) surface and yielded a coverage independent isosteric heat of adsorption of 77 ± 4 kJ mol . No CO dissociation was observed on this surface. From CO adsorption isotherms studies on different adlayers, containing carbon and/or oxygen on Fe(100) at 300 K, it can be concluded that less CO is adsorbed when the surface contains more oxygen. A quantitative description of the CO isotherms can only be given by assuming the adsorbing surface to be heterogeneous.