Charge sensitivity analysis of oxide catalysts: TiO 2 (110) and (100) surface model clusters and H 2O adsorption

Abstract

Semiempirical charge sensitivity analysis (CSA) in the atoms-in-molecules (AIM) resolution has been used to predict catalytic activity towards the water adsorption of realistic cluster representations of the TiO 2 (110) and (100) surfaces. The input hardness tensors have been generated on the basis of Sindo1 atomic charges of the symmetry-restricted optimized cluster geometries. The mechanism of the H 2O adsorption and dissociation on the catalytically more active TiO 2 (110) surface is reexamined in terms of relevant AIM Fukui function data and related charge sensitivities of the eigenvectors of the hardness tensor. The chemisorption data for the molecular adsorption of H 2O on the preferred five-fold coordinated Ti site are used to predict the course of the charge transfer included dissociation of the adsorbate, in which the H is released and combined with the lattice O 2− to form another OH fragment. A small energy barrier of ∼ 5 kcal/mol for this process is estimated from Sindo1 calculations. This corresponds to the transition structure of a tilted molecule and further supports the predicted course of the water dissociation. An effect is observed of the enhanced reactivity of a top Ti site due to the presence of the rutile second-layer atoms.