Synthesis of highly dispersed gold nanoparticles on Al₂O₃, SiO₂, and TiO₂ for the solvent-free oxidation of benzyl alcohol under low metal loadings

We reported the organic template-free synthesis of gold (Au) nanoparticles (NPs) supported on TiO₂, SiO₂, and Al₂O₃ displaying uniform Au sizes and high dispersions over the supports. The Au-based catalysts were prepared by a deposition–precipitation method using urea as the precipitating agent. In the next step, the solvent-free oxidation of benzyl alcohol was investigated as model reaction using only 0.08–0.05 mol% of Au loadings and oxygen (O₂) as the oxidant. Very high catalytic performances (TOF up to 443,624 h⁻¹) could be achieved. Specifically, we investigated their catalytic activities, selectivity, and stabilities as well as the role of metal–support interactions over the performances. The conversion of the substrate was found to be associated with the nature of the employed support as the Au NPs presented similar sizes in all materials. A sub-stoichiometric amount of base was sufficient for the catalyst activation and the observation of the catalysts profile over the time enable insights on their recyclability performances. We believe this reported method represents a facile approach for the synthesis of uniform Au-supported catalysts displaying high performances.