Gold nanoparticles deposited on Amberlyst-15: Metal–acid bifunctional catalyst for cellobiose conversion to gluconic acid

•Au solid-acid catalysts were prepared by alkaline impregnation of gold acetate.•Au nanoparticles (<8nm) were deposited on amorphous SiO2–Al2O3 and Amberlyst-15.•Acidic form of the catalyst was obtained by the proton exchange after Au deposition.•Acidic Au/Amberlyst-15 was efficient for metal–acid bifunctional catalysis.•The catalyst afforded the direct conversion of cellobiose to gluconic acid at 373K.