Adsorption of carbonate species on silver. I. Nature of the surface bond

Abstract

The adsorption of carbon trioxide, carbonate and bicarbonate is investigated on the 111, 110 and 100 surfaces of silver from a quantum mechanical point of view. Several aspects of the metal/ion bonding such as the adsorbate binding energy, charge transfer to/from the metal and the relaxation of the adsorbates upon adsorption are investigated. On the hollow site of Ag(110) bicoordinated carbonate has a binding energy of 226.9 kcal/mol. The highest binding energies for carbonate are obtained on Ag(110) while on Ag(111) and Ag(100) comparable binding energies are observed. The bicarbonate ion has a binding energy of 74.0 kcal/mol bicoordinated on the hollow site of Ag(100). The binding energy of bicoordinated CO 3 is 117 kcal/mol on Ag(100). There is a charge transfer towards the metal of 0.5 electrons in the case of carbonate and 0.25 electrons for bicarbonate. On the other hand, CO 3 adsorption leads to a charge transfer of 1.5 electrons from the metal to the adsorbate. Adsorbed carbonate and carbon trioxide have the same formal charge of −1.5 electrons and the same geometry, which is very close to that of carbonate compounds. For all adsorbates, the geometry distortion upon adsorption follows the same trend: the carbon-coordinated oxygen bond length increases while the bond length between the carbon atom and the non-coordinated oxygen atom decreases. The changes in bond lengths induced by the adsorption process are between 4 to 8%.