Adsorption of CO and CN− on transition metal surfaces: a comparative study of the bonding mechanism

A comparative study of the chemisorption of the isoelectronic species CO and CN− on Rh, Ni, Pd and Pt(1 1 1) surfaces has been performed using the cluster model approach and the density functional theory. The CO bond is weakened whereas the CN− one is strengthened upon chemisorption in agreement with experimental evidence based on shifts to lower or higher frequencies, respectively, with respect the vibrational frequency of the free adsorbate. The details of the chemisorption bond have been studied using different techniques including a topological analysis of the electron localization function and the projection orbitals method. Finally, a correlation between the substrate–adsorbate charge transfer and the frequency shift has been found.