The adsorption and dissociation of ROH molecules on TiO 2(110)

Abstract

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 H 2O, CH 3OH, H 2O 2 and HCO 2H on the TiO 2(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 ∼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 H 2O, CH 3OH and H 2O 2. For HCO 2H, 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 TiO 2(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.