Effect of the Colloidal Preparation Method for Supported Preformed Colloidal Au Nanoparticles for the Liquid Phase Oxidation of 1,6-Hexanediol to Adipic Acid

Supported on activated carbon gold colloidal nanoparticles have been prepared in the presence of the stabilizing polymer PVA and PVP (polyvinylalcohol, polyvinylpyrrolidone). The effect of the polymer to the Au weight ratio was investigated, for synthesizing gold nanoparticles with different particle size and particle size distribution. By varying the polymer/Au wt/wt ratio, gold nanoparticles with mean diameters from 3 to 8 nm were synthesized. The synthesized Au catalysts were studied in the liquid phase oxidation of 1,6-hexanediol (HDO) to adipic acid under base and base-free conditions. A range of experimental parameters were varied for the optimization of reaction conditions and the most promising Au catalysts were further evaluated in terms of catalytic performance. We demonstrated that the influence of choice of polymer, tuning the polymer to Au weight ratio, HDO to Au molar ratio, and use of basic conditions have an important influence in terms of catalytic activity and selectivity to adipic acid. The highest yield to adipic acid was obtained using Au-PVA catalysts (40% at 110 degrees C under base free conditions), however, at low HDO to Au molar ratio and lower carbon balance (70-80%). On the contrary, at higher HDO to Au molar ratio, and under basic conditions, the yield was in the range of 18-20% with a significant improvement in terms of carbon balance (88-100%).