Selective lactose oxidation in aqueous-phase over Ag-Au bimetallic nanoparticles supported on Al2O3 under mild reaction conditions

•A bimetallic Au-Ag phase on Al2O3 can be obtained by precipitation-deposition at controlled pH.•Lactose oxidation rate and nanostructure of Au-Ag/Al2O3 strongly depend on the Au/(Au + Ag) ratio.•When Au/(Ag + Au) ≥ 0.5, Ag incorporates to the Au nanocrystallites surface by migration-diffusion mechanism.•When Au/(Au + Ag) < 0.5, bimetallic nanoparticles are covered by an Ag layer and are non-actives.•The optimum catalytic performance in aqueous-phase lactose oxidation was reached with Au/(Au + Ag) = 0.9.