Preparation of supported gold nanoparticles by a modified incipient wetness impregnation method.

In this work, we show that if the mere procedure of impregnation of oxide supports with chloroauric acid, which is well-known to lead to large gold particles, is followed by a step of washing with ammonia, small gold particles (3-4 nm) can be obtained after a treatment of calcination at 300 degrees C on any type of oxide supports (alumina, titania, silica). Moreover, gold leaching is very limited during the washing step, and a large range of gold loadings (0.7-3.5 wt %) can be achieved. Elemental analysis, Raman spectroscopy, and temperature programmed desorption under argon show that this ammonia posttreatment results in the removal of chloride ligands from the coordination sphere of Au(III) precursor and their replacement by ammine ligands, leading to an ammino-hydroxo or an ammino-hydroxo-aquo gold complex and not to gold hydroxide. The Au/TiO(2) catalysts prepared with this modified procedure of impregnation are almost as active as those prepared by deposition-precipitation with urea in the CO oxidation reaction performed at room temperature.