Effect of the preparation method of supported Au nanoparticles in the liquid phase oxidation of glycerol

Catalytically-active gold nanoparticles that are stable in aqueous solution have been prepared by sodium borohydride reduction of the respective metal salts in the presence of the stabilising polymer PVA (polyvinylalcohol). By controlling the ratio of the polymer to the metal, nanoparticles with different particle size and size distribution were synthesised. By varying the concentration of the gold and PVA/Au wt/wt ratio, well-defined nanoparticles with mean diameters from 3 to 5 nm could be fabricated. In general increasing the concentration of Au precursor, bigger particles size were obtained. Furthermore decreasing the amount of PVA, bigger particles were obtained, with the exception of the catalysts synthesized in presence of a large amount of PVA (PVA/Au = 2) wt/wt. Probably, in presence of an excess of protective agent, the immobilization of the Au nanoparticles onto the support is more difficult, leading to partial aggregation and coalescence of Au. In addition, the studies on the effect of heat pre-treatment revealed a higher resistance to aggregation of Au nanoparticles supported on titania than on activated carbon. A selected series of the synthesised supported materials were studied in the liquid phase oxidation of glycerol with the purpose of correlating catalytic activity and selectivity with particle size and metal choice. We demonstrated that by both particles size and amount of protective agent strongly influence the activity and selectivity.