The effects of carbon, oxygen, sulfur and potassium adlayers on CO and H 2 adsorption on Fe(100)

Abstract

The adsorption and desorption of CO and hydrogen was studied on clean Fe(100) and Fe(100) with adiayers of carbon, oxygen, sulfur, and potassium using X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption. Hydrogen was found to be dissociatively adsorbed on Fe(100) with a binding energy of 86 kJ/mole. CO absorption was found to be complex, involving several molecular binding states as well as dissociated CO. The activation energy for dissociation of CO on Fe(100) was estimated to be 105 kJ/mole. Sulfur, oxygen, and carbon adlayers all reduced the binding energies for CO and hydrogen and inhibited CO dissociation. Potassium was observed to enhance the CO and hydrogen binding strengths and increase the amount of CO dissociation relative to the clean surface. These results have been compared to LCAO calculations for CO adsorption on an Fe(100) surface with adiayers. The model calculations showed that adiayers of carbon, oxygen, and sulfur reduced the CO binding energy on Fe(100) by bonding with the same Fe(3d) orbitals as the CO(2π ∗) orbitals would. Potassium was found to enhance the CO binding energy on Fe(100) due to interactions between the K(4s) orbital and the CO(2π ∗) orbitals.