Magnesium surface enrichment of CoFeO magnetic nanoparticles immobilized with gold: reusable catalysts for green oxidation of benzyl alcohol.

Gold nanoparticles have shown excellent activity for selective oxidation of alcohols; such catalytic systems are highly dependent on the initial activation of the substrates, which must occur on the catalyst surface in heterogeneous catalysts. In many cases, an extra base addition is required, although the basicity of the support may also be of significant importance. Here, we explored the intrinsic basicity of magnesium-based enrichments on CoFeO magnetic nanoparticles for the oxidation of benzyl alcohol using molecular oxygen as oxidant. The MgO and Mg(OH) enrichments enabled gold impregnation, which was not possible on the bare CoFeO nanoparticles. The Au/MgO/CoFeO and Au/Mg(OH)/CoFeO catalysts reached 42% and 18% conversion, respectively without base promotion, in 2.5 hour and 2 bar of O. When the catalysts were tested with sub-stoichiometric amounts of base, they became more active (>70% of conversion) and stable in successive recycling experiments without metal leaching, under the same reaction conditions. We also showed the oxide phases of the enrichments performed using Rietveld refinements and how the Mg(OH) phase interferes with the activity of MgO-based materials.