Dendrimer derived titania-supported Au nanoparticles as potential catalysts in styrene oxidation

Titania-supported Au nanoparticles were prepared from Au dendrimer encapsulated nanoparticle (DEN) precursors. The Au-DENs were synthesised using generation 4 amine terminated poly(amido amine) (G4-PAMAM-NH₂) dendrimer templates, and were prepared for immobilisation onto titania supports via either the sol-gel method or via wet impregnation (the average particle sizes were 2.3 ± 0.4 and 1.9 ± 0.4 nm for the respective methods). The dendrimer template was removed by calcination at 500 °C, resulting in the immobilisation of Au nanoparticles onto titania. The wet impregnation and sol-gel methods led to an increase in the average particle size of 7.6 ± 2.2 and 7.1 ± 2.0 nm respectively, following the calcination. The catalyst prepared via the wet impregnation method was found to have higher metal loading (1.8 wt%) than the one prepared using the sol-gel method (1.3 wt%). The catalytic activity of these supported Au nanoparticles was evaluated in the oxidation of styrene by tert-butyl hydroperoxide. Both catalysts produced benzaldehyde and styrene oxide as major products although benzalydehyde was favoured. The catalyst prepared via the sol-gel method catalysed the highest styrene conversion at 41 % and the highest conversion for the catalyst prepared using the wet impregnation method was 25 %.