Alternative methods for the preparation of gold nanoparticles supported on TiO2

The best current way to prepare Au/TiO2 catalysts is the method of deposition-precipitation with NaOH (DP NaOH) developed by Haruta and co-workers. With this method, it is possible to obtain small gold metal particles (2-3 nm), but the corresponding gold loading remains rather low (similar to3 wt %). The main goal of this work is to investigate other methods of preparation of Au/TiO2 catalysts to obtain small gold metal particles (2-3 nm) and a higher Au loading. It is shown that anion adsorption with AuCl4- (AA) does not produce Au loading higher than 1.5 wt % and the average particle size is not very small (similar to4 nm), Cation adsorption with Au(en)(2)(3+) (CA) leads to small particles (2 nm) when the solution/support contact time is moderate (I h), but the Au loading does not exceed 2 wt %. The most promising method of preparation appears to be deposition-precipitation with urea (DP urea). Indeed, samples with gold particles as small as those obtained with DP NaOH (similar to2 nm) can be prepared, and all gold in solution is deposited on TiO2 in contrast to DP NaOH. The DP urea samples reported in this paper can reach a Au loading as high as 8 wt % using a TiO2 support with a surface area of 45 m(2) g(-1). The possible mechanisms of deposition of gold on the TiO2 support by the different methods of preparation are discussed.