The bonding of CO to metal surfaces

Abstract

The atom and symmetry specific properties of x-ray emission spectroscopy have been applied to the investigation of CO adsorbed on Ni(100) and Cu(100) surfaces. In comparison to ab initio electronic structure calculations, obtained in density functional theory, we develop a consistent electronic structure model of CO adsorption on transition and noble metals and extend to a conceptual model of the surface chemical bond. A strong CO–substrate interaction is found, characterized by significant hybridization of the initial CO orbitals and the metal bands. In the π system an allylic configuration is found as the result of orbital mixing between the CO 1π, 2π* and the metal dπ-band which is manifested experimentally in the observation of an oxygen lone-pair state. In the σ system experimental evidence of equally strong orbital mixing has been found. Energetically, the adsorbate–substrate complex is stabilized by the π-interaction but is destabilized by the σ-interaction. Furthermore, the internal C–O bond carried by the π-interaction is weakened upon adsorption, which is opposite for the internal C–O σ bond that is strengthened. The equilibrium properties of CO adsorbed on these metals are found to be the direct result of the balance between the σ- and π-interactions; both in terms of the total energy and the local bond properties.

Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction

“…[42][43][44] Both depend on the d-band position, however, the σ-repulsion is also sensitive to the occupancy of the Cu sp-band. Thus an electron acceptor which withdraws charge from the sp-band can reduce the repulsion as shown by Xin et al for the case 2O-CO/Ru(0001).…”

CO adsorption on metal surfaces: A hybrid functional study with plane-wave basis set

“…The 1π states are found at ∼ −7 eV (dotted line), and a small peak of 2π * symmetry at the position of the 1π orbital is visible and related to the 1π − 2π * hybridization. 66 Above −6 eV, a non-bonding and antibonding 1π−derived band develops (d π band) 66 The down-shift of the d band and simultaneous up-shift of the 2π * levels suggest a reduced 2π * −d interaction: according to second order perturbation theory, the larger energy distance between the unperturbed energy levels weakens the interaction. Inspection of the calculated DOS confirms this conjecture for HSE03: i) the d π peaks are much weaker, ii) hybridization between 2π * and 1π molecular orbitals decreases corresponding to a decrease of the bonding interaction between the CO π−states and the metal d states according to Föhlisch.…”

The screening effects of the screened exchange hybrid functional in surface systems: A case study on the CO/Pt(111) problem

“…47 Upon CO adsorption, there is significant mixing of the adsorbate 1π and 2π orbitals (the latter accounts for back-donation) with the metal d band, generating three new hybrid π orbitals in an allylic configuration. 48,49 Thus a band is formed by an antibonding 1π and a bonding 2π admixture to the metal d band, leading to a cancellation of orbital amplitude at the carbon and an increase at the oxygen. From the DOS, we also see that the 5σ state lies at lower bonding energy for the fcc site adsorption than that for the atop adsorption as calculated by each functional, respectively.…”