Supported gold nanoparticles for sustainable catalytic applications

The objectives of the present work are to investigate the influence of stabilizers in colloidal methods (sol-immobilization method) for the synthesis of preformed Au colloidal nanoparticles and the immobilization of the synthesized Au colloidal nanoparticles on supports, like activated carbon. By varying the nature of stabilizer (PVP, PEG, and PVA) and the weight ratio of stabilizer to metal, a number of Au based catalysts were prepared and the catalytic performance of the synthesized catalysts was tested for a range of model reactions. To determine the morphology of the unsupported and supported metal nanoparticles, several characterization techniques were used (UV-Vis, XRD, TEM, and XPS) to determine the mean particle and crystallite size of Au, the particle size distribution, the oxidation state of the Au, and the surface coverage of Au onto the support. From TEM analysis, it can be shown that in the absence of the polymer that acts as stabilizing agent gives worst dispersion of the Au nanoparticles on the support, affects thermal stability of the supported Au nanoparticles, enhance the agglomeration of the Au nanoparticles for reactions at high reaction temperature and decrease the number of active sites. However, from XPS analysis it was observed that at high polymer:Au weight ratio (more than 1.2) may increase the coverage of the gold nanoparticles on the surface, causing a decrease in the value of Au available on the catalyst surface. A series of catalysts were synthesized and the catalytic performance was investigated for each reaction: Glucose oxidation to glucaric acid, HMF oxidation to 2,5-furandicarboxylic acid, oxidation of 1,6 Hexanediol to Adipic acid, furfural oxidative condensation and oxidative esterification, 4-Nitrophenol reduction to 4-aminophenol. The optimum polymer:Au weight ratio in terms of catalytic performance for each reaction is not the same and an explanation could be attributed to the different reaction conditions used.