An ONIOM and DFT Study of Water and Ammonia Adsorption on Anatase TiO2 (001) Cluster

Density functional theory (DFT) calculations at ONIOM DFT B3LYP/6-31G**-MD/UFF level are employed to study molecular and dissociative water and ammonia adsorption on anatase TiO2 (001) surface represented by partially relaxed Ti20O35 ONIOM cluster. DFT calculations indicate that water molecule is dissociated on anatase TiO2 (001) surface by a nonactivated process with an exothermic relative energy difference of 58.12 kcal/mol. Dissociation of ammonia molecule on the same surface is energetically more favorable than molecular adsorption of ammonia (-37.17 kcal/mol vs. -23.28 kcal/mol). The vibration frequency values also are computed for the optimized geometries of adsorbed water and ammonia molecules on anatase TiO2 (001) surface. The computed adsorption energy and vibration frequency values are comparable with the values reported in the literature. Finally, several thermodynamical properties (Delta H degrees, Delta S degrees, and Delta G degrees) are calculated for temperatures corresponding to the experimental studies. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 2149-2159, 2011