Effects of morphology on surface hydroxyl concentration:: a DFT comparison of anatase-TiO2 and γ-alumina catalytic supports

A comparative investigation of surface hydroxylation states for anatase-TiO2 and gamma-alumina is crucial for a better understanding of how these materials behave as catalytic supports under working conditions. Our approach combines density functional simulations and thermodynamic analysis, to determine the types of hydroxyls existing on the (100), (101), (001), and (110) surfaces of anatase-TiO2, as a function of temperature and water pressure. The vibrational analysis of surface OH groups allows for the assignment of experimental infrared bands as a function of the surface orientation. A consistent and quantitative comparison with recent DFT simulations on gamma-alumina highlights the different acidic-basic properties of the two supports. Finally, we suggest directions for increasing the density of basic and exchangeable hydroxyls which is governed by morphology effects. (C) 2003 Elsevier Inc. All rights reserved.