Supported Gold Nanoparticles as Reusable Catalysts for Oxidation Reactions of Industrial Significance.

The efficient single-pot oxidative functionalisation of alkanes and alcohols under mild conditions was catalysed by Au nanoparticles supported on Al₂O₃, Fe₂O₃, ZnO and TiO₂. The obtained materials were tested for cyclohexane oxidation under mild conditions (60 °C, atmospheric pressure) using an environmentally friendly oxidant (H₂O₂). The materials were also tested in the oxidation of benzyl alcohol and methylbenzyl alcohol in the presence of tert-butylhydroperoxide as the oxidant under microwave irradiation. With regard to cyclohexane oxidation, all materials were highly selective towards the formation of cyclohexanol and cyclohexanone. No traces of byproducts were detected under the optimised conditions. Au on Fe₂O₃ led to the best results (13.5 % yield). This system showed an interesting almost exclusive formation of cyclohexanol at 4 h reaction time. Catalyst recycling was tested in up to five cycles, and the catalyst maintained almost the original level of activity after three cycles with no significant leaching. With regard to oxidation of benzyl alcohol and methylbenzyl alcohol, all materials were highly selective towards the formation of benzaldehyde or acetophenone, respectively. No traces of byproducts were detected. Addition of Au increased alcohol conversion from 5 (TiO₂) to 91 % (Au/TiO₂). The recycling of Au/TiO₂ was tested in up to 10 cycles, and the catalytic activity remained high in the first four cycles. [ABSTRACT FROM AUTHOR]