Aerobic oxidation of alcohols on Au nanocatalyst: Insight to the roles of the Ni-Al layered double hydroxides support

Abstract

Au nanoparticles (NPs) supported on Ni-Al layered double hydroxides (LDHs) were shown to be efficient heterogeneous catalysts for the highly selective oxidation of alcohols to the corresponding aldehydes or ketones under base-free or even solvent-free conditions with O2 as the sole oxidant. The Au NPs can be uniformly distributed on Ni-Al LDHs support, which is beneficial to the catalytic activity. In addition, the weak Brønsted basic property of the support enables the aerobic oxidation of alcohols under base-free conditions. More importantly, unlike Al2O3, which is inert, Ni-Al-LDHs are redox-actively involved in prompting the electron transfer to O2 via the Au nanocatalyst because of the presence of Ni II. Both of the basic and the redox properties of Ni-Al-LDHs can be tuned by adjusting the ratio of Ni:Al to achieve the best synergistic effects between Au NPs and the supports. The activity of the obtained Au catalysts was found to be structurally associated with the arrangements of NiO6 and AlO6 octahedra in the surface hydroxide layers which were different from the bulk Ni:Al ratio. Gold-support synergy: Au nanoparticles supported on Ni-Al layered double hydroxides exhibit high chemoselectivity, recyclability, and reproducibility for the liquid-phase aerobic oxidation of alcohols under base-free or even solvent-free conditions. The synergistic effect between the nanoparticles and the layered double hydroxide support dominates the unique catalytic activity, which is also correlated to the complete ordering of cations in the surface layers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.