CHARGE SENSITIVITY ANALYSIS OF OXIDE CATALYSTS - TIO2 (110) AND (100)SURFACE MODEL CLUSTERS AND H2O ADSORPTION

Semiempirical charge sensitivity analysis (CSA) in the atoms-in-molecu les (AIM) resolution has been used to predict catalytic activity towar ds the water adsorption of realistic cluster representations of the Ti O2 (110) and (100) surfaces. The input hardness tensors have been gene rated on the basis of SINDO1 atomic charges of the symmetry-restricted optimized cluster geometries. The mechanism of the H2O adsorption and dissociation on the catalytically more active TiO2 (110) surface is r eexamined in terms of relevant AIM Fukui function data and related cha rge sensitivities of the eigenvectors of the hardness tensor. The chem isorption data for the molecular adsorption of H2O On the preferred fi ve-fold coordinated Ti site are used to predict the course of the char ge transfer included dissociation of the adsorbate, in which the H is released and combined with the lattice O2- to form another OH fragment . A small energy barrier of approximately 5 kcal/mol for this process is estimated from SINDO1 calculations. This corresponds to the transit ion structure of a tilted molecule and further supports the predicted course of the water dissociation. An effect is observed of the enhance d reactivity of a top Ti site due to the presence of the rutile second -layer atoms.