The adsorption and dissociation of ROH molecules on TiO2(110)

First-principles calculations based on density-functional theory and the pseudopotential method are used to investigate the energetics of adsorption of the series of molecules H2O, CH3OH, H2O2 and HCO2H on the TiO2(110) surface. The aim of the work is to elucidate the factors that determine whether the adsorption is molecular or dissociative, including the acidity of the molecule, the geometry and electrostatic properties of the surface, and the interaction between adsorbed species. It is shown that the theoretical methods reproduce experimental values of the gas-phase heterolytic and homolytic dissociation energies to reasonable accuracy (within similar to 20 kJ mol(-1) for all four molecules). We find that the adsorption energy for the most favourable molecular mode of adsorption is extremely close to that for dissociative adsorption in the cases of H2O, CH3OH and H2O2. For HCO2H, dissociative adsorption is favoured by a substantial margin, provided the dissociated geometry preserves the equivalence of the two oxygens in the formate ion. It is also shown that the geometry of the TiO2(110) surface plays a crucial role in determining the conformations of the most stable geometries, and that hydrogen bonding between adsorbed species is also important. (C) 1998 Elsevier Science B.V. All rights reserved.