Solvent-free oxidation of toluene to benzaldehyde using electron-rich Au clusters confined in Silicalite-1

Abstract

The selective oxidation of the primary CH bonds in hydrocarbons to corresponding high-valued oxygenates is highly desired but challenging to realize. The difficulty arises from the high homolytic bond dissociation enthalpy of the CH bond, the relatively high reactivity of oxygenated intermediates, and the diversity of resultant products. Herein, we reported the in situ confinement of Au clusters in Silicalite-1 for the selective solvent-free oxidation of toluene to benzaldehyde. The doping of an alkali metal (K or Na) resulted in the formation of electron-rich Au species, which readily facilitate the activation of oxygen, In turn, toluene is activated by the produced reactive oxygen species in a single step, as confirmed through density functional theory (DFT) calculations. At optimal alkali metal doping, the selectivity to benzaldehyde could reach > 90 %, with the toluene conversion being 19.8 %. Remarkably, the total turnover number (TTN) of Au@Silicalite-1–0.2 K was found to be 29,658, which is one or two orders of magnitudes higher than the previously reported values. These findings are expected to inspire the design of highly efficient catalysts for the activation of fundamental feedstock with CH bonds.