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

This paper reports on the single-pot efficient oxidative functionalization of alkanes and alcohols, under mild conditions, catalysed by Au nanoparticles supported on Al2O3, Fe2O3, ZnO and TiO2. The obtained materials were tested for cyclohexane oxidation under mild conditions (60oC, 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 t-butyl hydroperoxide as oxidant, under microwave irradiation. Concerning cyclohexane oxidation, all materials were highly selective towards the formation of cyclohexanol and cyclohexanone. No traces of by-products were detected under optimized 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 up to 5 cycles, and the catalyst maintained almost the original level of activity after 3 cycles with no significant leaching. Concerning the oxidation of benzyl alcohol or methylbenzyl alcohol, all materials were highly selective towards the formation of benzaldehyde or acetophenone, respectively. No traces of by-products were detected. Addition of Au increased the alcohol conversion from 5% ( TiO2) to 91% (Au/TiO2), the latter being the best result obtained in this work. Recycling of Au/TiO2 was tested up to 10 cycles and catalytic activity remained at high level in the first 4 cycles.