Solvent-free oxidation of 1-phenylethanol catalysed by gold nanoparticles supported on carbon powder materials

Gold (1 wt.%) was loaded on several carbon materials, namely, polymer based carbon xerogel, activated carbon, microdiamonds, nanodiamonds, graphite and silicon carbide by double impregnation and sol immobilisation. The obtained catalysts were characterised by N₂ adsorption at -196 ºC, high-resolution transmission electron microscopy, high-angle annular dark-field imaging (Z-contrast), temperature programmed desorption, atomic absorption spectroscopy and X-ray photoelectron spectroscopy. The obtained materials were tested on the microwave-assisted solvent-free oxidation of 1-phenylethanol by tert-butyl hydroperoxide (TBHP) to produce acetophenone. The results showed that the catalytic activity was influenced by several factors, namely, the nature of the support, reaction time and temperature, amount of catalyst, presence of additives, among others. The best values for acetophenone yield (99.9%) were obtained with Au deposited on microdiamonds by the colloidal method. Catalyst recyclability was tested up to six consecutive cycles at the optimized conditions for each catalyst, and it was found that Au on microdiamonds, prepared by the colloidal method, also maintained higher activity after several reaction cycles as compared to the other carbon supports.