Preparation and reactivation of Au/TiO2 catalysts

In the preparation of Au/TiO2 (P-25) catalysts by the method commonly but inaccurately known as deposition-precipitation (DP), the uptake of anionic complexes in solution onto the support is maximal close to the pH of the isoelectric point (similar to 6); below this pH, complexes are adsorbed electrostatically, but at higher pH values, especially at pH 8-9, the neutral Au(OH)(3)center dot H2O is reversibly adsorbed on the negatively charged surface. The specific activity (per gram of gold) peaks however at pH 8-9, because here the adsorbed complex is largely chlorine-free. The reversibility of the adsorption equilibrium is proved by alteration of the pH during the course of a single preparation through analysis of samples removed at intermediate points. This observation enables poorly dispersed precursors or sintered gold particles to be re-dispersed, and high activity restored. (C) 2007 Elsevier B.V. All rights reserved.