Density functional studies of molecular chemisorption on TiO2 (110)

The molecular adsorption of CO and H2O on TiO2 (110) surface is studied within the density functional theory by using cluster models terminated with pseudo-hydrogen saturators. Structural properties of the clean surface, adsorption energies and adsorbate vibrations are computed in good agreement both with experiment and with periodic slab calculations. Results are shown to converge rapidly with cluster size: a small Ti7O9 cluster is able to represent adequately the surface Lewis acid site. This is tin indication that local effects are predominant in determining chemisorption on TiO2. Only the HOH scissoring mode is poorly reproduced, suggesting that molecularly adsorbed H2O is involved in weak bonds with other adsorbed species.