A Comparative Study of the CO Chemisorption on Ti2O3(10-12) and V2O3(10-12) Non-Polar Surfaces

Density functional molecular cluster calculations have been used to investigate the coordination of CO to Lewis acid sites (Lsa) available on Ti2O3(10-12) and V2O3(10-12) non-polar surfaces. The electronic structure of the clean substrates, the adsorbate geometry and chemisorption enthalpies are computed and discussed. Properties of the clean surfaces are well described by the chosen cluster models. Moreover, the Lsa–CO bonding is found to be very similar to that holding for transition metal carbonyls: i.e., a two-way electron flow implying a σ donation from the CO 5σ HOMO into empty Lsa AOs, assisted by a π backdonation from Lsa occupied orbitals into the CO 2π LUMO. Both the electronic and molecular structure of the adsorbate are significantly perturbed upon chemisorption and, consistently with experimental data, the C–O bond results strongly weakened. The chemisorption enthalpy of CO on V2O3(10-12) (∼−30 kcal/mol) is about twice that computed for CO on Ti2O3(10-12) (∼−16 kcal/mol).