Abstract
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 °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%).
Highlights
Introduction1,6-Hexanediol (HDO) is an emerging building-block chemical, which may be generated from biomass and transform to adipic acid (AA)
The synthesized Au colloidal nanoparticles with PVA and PVP as the chosen stabilizers and different stabilizer/Au weight ratio were analyzed by UV–visible spectroscopy
The influence and the amount of stabilizer was investigated in the presence of preformed supported Au colloidal nanoparticles, using activated carbon as the preferred choice of support, for the selective aqueous phase oxidation of 1,6-hexanediol to adipic acid in the absence and presence of base (NaOH)
Summary
1,6-Hexanediol (HDO) is an emerging building-block chemical, which may be generated from biomass and transform to adipic acid (AA). AA is one of the key aliphatic dicarboxylic acids widely used in chemical industries as a starting material in the polyamide (nylon-6,6) synthesis. It is generally used for the production of aliphatic esters, lubricants, and many other applications [1,2]. AA used in chemical industry is generally produced in a two-step oxidation process. The first step is carried out using air as oxidant and the second using an Catalysts 2022, 12, 196 excess of excess
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