THE ADSORPTION AND DISSOCIATION OF ROH MOLECULES ON TIO2(110)

First-principles calculations based on density-functional theory and t he pseudopotential method are used to investigate the energetics of ad sorption 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 tha t determine whether the adsorption is molecular or dissociative, inclu ding the acidity of the molecule, the geometry and electrostatic prope rties of the surface, and the interaction between adsorbed species. It is shown that the theoretical methods reproduce experimental values o f the gas-phase heterolytic and homolytic dissociation energies to rea sonable accuracy (within similar to 20 kJ mol(-1) for all four molecul es). We find that the adsorption energy for the most favourable molecu lar mode of adsorption is extremely close to that for dissociative ads orption in the cases of H2O, CH3OH and H2O2. For HCO2H, dissociative a dsorption is favoured by a substantial margin, provided the dissociate d geometry preserves the equivalence of the two oxygens in the formate ion. It is also shown that the geometry of the TiO2(110) surface play s a crucial role in determining the conformations of the most stable g eometries, and that hydrogen bonding between adsorbed species is also important. (C) 1998 Elsevier Science B.V. All rights reserved.