Molecular and dissociative adsorption of CO and SO on the surface of Ir(111)

This study investigates the molecular and dissociative adsorption of CO and SO molecules on the perfect and a defective Ir(111) surface. It is aimed at providing a broad spectrum of adsorption sites in terms of coordination of Ir atoms and investigating the role of surface defects on the adsorption of small molecules on the surface Ir(111). First-principles density functional theory (DFT) simulation with the generalized gradient approximation as it is implemented in Vienna ab initio simulation package has been employed for this study. Preferred adsorption sites, adsorption energies, and surface electronic structures of CO and SO molecules on the perfect and defective Ir(111) surfaces were calculated to obtain a systematic understanding on the nature of adsorption and dissociative interactions. The DFT calculation reveals the possible molecular adsorption of CO on both perfect and defective Ir(111) surface by the end-on manner (CO bond perpendicular to the surface); the later surface is found to be energetically more favorable. However, no dissociative adsorption was obtained. For SO molecule, on the other hand, both molecular and dissociative adsorption was observed. The defective surface is now less favorable in terms of adsorption energy, but yields stronger activation of SO. The nudged elastic band method investigation also reveals that the Pt single-atom catalysis significantly reduces (up to 80% reduction) the energy barrier of the dissociative adsorption of SO. The electronic structure calculation reveals that all the adsorptions investigated in this study involve hybridization of different electronic states.