Colorless alkaline solution of chloride-free gold acetate for impregnation: An innovative method for preparing highly active Au nanoparticles catalyst

Abstract

An easy and versatile method for the preparation of gold nanoparticles catalyst from aqueous alkaline solution of chloride-free gold acetate has been developed. Au nanoparticles can be deposited on various supports only by impregnating them with the stocked solution of it and by the following calcination. Although the solubility of gold acetate is considerably low in water, we have successfully dissolved it completely by refluxing the brown colloidal dispersion of gold acetate with a pH adjusted to 10–11 at the boiling temperature. The resultant solution was transparent without any color, which should contain anionic Au(III) species like Au(OH)4−. Metal oxide powder such as Al2O3, CeO2, TiO2, SiO2 as well as silicates such as saponite clay, and Y-type zeolites was impregnated with the solution and then calcined at 623K. After washing and drying, the deposition of Au nanoparticles (<6nm) was confirmed by TEM, XRD and EXAFS on any supports regardless of their widely different isoelectric point. For gas phase CO oxidation, the Au/CeO2 prepared by this method was more active than those prepared according to conventional deposition–precipitation or impregnation methods by using HAuCl4 as a source of gold. The smallest mean particle size of Au (2.3±0.8nm) was obtained on saponite clay, which was highly active for glucose oxidation performed in aqueous phase at 333K.