Adsorption of Methanol on TiO₂(110):  A First-Principles Investigation

We have performed first-principles static and dynamic calculations based on density functional theory and the pseudopotential method to investigate the adsorption and deprotonation of methanol on the stoichiometric (110) surface of TiO 2 . Static calculations, employing full relaxation of adsorbate and substrate atom positions, are performed. In the high-coverage limit (θ = 1), we find that there are several structures of approximately equal stability. In two of these, the methanol molecule is dissociated, resulting from scission of the O−H or C−O bonds. In the third, methanol is molecularly adsorbed. Other structures of approximately equivalent energy contain 1:1 mixtures of these conformations. At lower coverage (θ = 1 / 2 ), we find that the two dissociative modes of adsorption found at θ = 1 are favored over molecular adsorption by 19 kJ/mol (O−H scission) and 7 kJ/mol (C−O scission). The adsorption energy of the most stable θ = 1 / 2 conformation changes by approximately ±5% as the coverage is reduced to θ = 1 / 3 and θ = 1 / 4 . Intermolecular attractions and repulsions are found to play a crucial role in determining the stability of different conformations at different coverages. Conversion of the metastable θ = 1 / 2 molecularly adsorbed complex via O−H scission to a dissociated complex is predicted to be barrierless. First-principles molecular dynamics calculations on this system in which the methanol molecule approaches the surface predict spontaneous dissociation by rupture of the O−H bond and also that C−O bond breaking is likely to be an activated process. Further dynamical simulations indicate that the probability of finding conformations other than that obtained after O−H bond rupture is small.