Adsorption of the formyl species on transition metal surfaces

The density functional theory (DFT) and the cluster approach were used to get information concerning the adsorption of the formyl species on transition metal surfaces. At first, the adsorption of HCO on four different sites of the Cu (111) surface was studied. An initial eta(1)-HCO-C conformation was considered in all cases. After optimisation, results obtained pointed towards a preferred eta(1)-HCO-C adsorption conformation with the carbon atom located between a bridge and a hcp hollow site. The calculated adsorption energy is approximately 140 kJ mol(-1). The internal geometrical parameters of the adsorbed species lie in between the calculated bond lengths and angles of the gas phase HCO and HCO- species. Adsorption of the formyl species on the Au (111) and Pt (111) surfaces was also studied. Starting from the optimised internal geometry of the adsorbed HCO species, a small adsorption energy on the gold surface, approximate to 52 kJ mol(-1), and a large adsorption energy on the platinum surface, approximate to 252 kJ mol(-1) were calculated. The distance from the carbon atom to the metallic surface is 1.9 Angstrom on copper, 2.2 Angstrom on gold and 1.5 Angstrom on platinum. Small C-surface distances led to large C-O bond lengths. The short carbon to surface distance in HCO adsorption on platinum when compared with copper and gold may be responsible for the distinct methanol oxidation on this surface. Calculated vibrational frequencies are in good agreement with previous theoretical and experimental data. The bonding to the surface has a mainly ionic character on copper and a more covalent one on platinum. (C) 2000 Elsevier Science S.A. All rights reserved.