A quantum-mechanical study of CO adsorbed on TiO2:: A comparison of the Lewis acidity of the rutile (110) and the anatase (101) surfaces

The adsorption of carbon monoxide on the rutile (110) and the anatase (101) surfaces has been investigated by a periodic approach using hybrid-exchange density functional theory: the quantum-mechanical study on the CO adsorption on the anatase surface has been carried out for the first time. The full optimization of the systems has been performed by considering different surface coverages and periodicities. The adsorption energetics have been investigated, on the basis of a recently proposed model, in terms of interaction, distortion and binding energies and the lateral effects have been analyzed using a simple model of nearest and next-nearest neighboring molecules. The experimental adsorbed CO stretching frequencies have been compared with the computed ones obtained by considering the highest investigated periodicity. The Lewis acidity of the two surfaces is comparable and the rutile (110) acid site seems to be slightly more electrophilic than that of the anatase (101) one. (C) 2008 Elsevier B.V. All rights reserved.