The materials were synthesized mechanochemically via ball milling according to previously published procedures. The synthesis details are available in the Electronic Supplementary Information (ESI). Metal-containing compounds in powder were milled in the presence of γ-AlOOH (bohemite), leading to the formation of metal NPs supported on HSA-α-Al 2 O 3 with a relative amount of metal with respect to support, in weight, of ca. 1%, noted 1 wt%. The synthesized materials were subjected to a thermal activation procedure consisting of a reduction step with H 2 and an annealing step.