Chloride-free and water-soluble Au complex for preparation of supported small nanoparticles by impregnation method

•Small Au nanoparticles (<3nm) were prepared on various supports by impregnation.•Chloride-free Au complex prevents Au atoms from aggregating.•Decomposition temperature of the Au complex is lower than that of HAuCl4.•The Au/SiO2 hydrogenates vinyl group of 1-nitro-4-vinylbenzene selectively.•The Au/SiO2 can be applied for adsorption of unpalatable aroma in drink.