Density functional studies of molecular chemisorption on TiO2 (110)

The molecular adsorption of CO and H2O on TiO2 (110) surface is studied wit hin the density functional theory by using cluster models terminated with p seudo-hydrogen saturators. Structural properties of the clean surface, adso rption energies and adsorbate vibrations are computed in good agreement bot h with experiment and with periodic slab calculations. Results are shown to converge rapidly with cluster size: a small Ti7O9 cluster is able to repre sent adequately the surface Lewis acid site. This is tin indication that lo cal effects are predominant in determining chemisorption on TiO2. Only the HOH scissoring mode is poorly reproduced, suggesting that molecularly adsor bed H2O is involved in weak bonds with other adsorbed species. (C) 1999 Els evier Science B.V. All rights reserved.