(268d) Exceptions to the d-Band Model of Chemisorption On Metal Surfaces: The Dominant Role of Repulsion Between Adsorbate States and Metal d-States

Developing predictive models of chemisorption on metal surfaces is critical for the understanding of surface chemical reactions. It has been shown that the d-band model of chemisorption, developed by Hammer and Nørskov, can predict the trends in chemisorption energies of various adsorbates on metal surfaces. The model correlates the central moment of the d-band projected on surface atoms (d-band center referenced to the Fermi level) with the surface reactivity. It has been used successfully to design novel metal surfaces for various catalytic reactions. In general, for a given adsorption geometry adsorbates bind to the surface of transition or noble metals more strongly if the d-band center of the surface atom is higher in energies.

In this presentation, we show that there is a family of adsorbate-substrate systems that does not follow the trends in adsorption energies predicted by the d-band model. A physically transparent model is used to analyze this phenomenon. We found that these adsorbate-substrate pairs are characterized by the repulsive interaction of the substrate d-band with the renormalized adsorbate states. The exceptions to the d-band model are mainly associated with the adsorbates having almost completely filled valence shell, and the substrates with nearly fully occupied d-band, i.e., OH, F or Cl adsorption on metals and alloys characterized by d9 or d10 substrate surface atoms.