Gold nanostructured materials for the selective liquid phase catalytic oxidation

Au(0) sols were obtained in aqueous solutions by reduction of NaAuCl4 with NaBH4 in the presence of protective agents [the long chain compound poly(oxyethylene(23)lauryl ether (C12E23), the polymer poly{bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea} (PEG), the poly quaternary salt obtained by reaction of a polyethyleneglycole with the bisphenol A diglycidyl ether (PEU), and a polysaccharide (dextrin)]. The sols, characterized by TEM microscopy and UV-Vis spectroscopy, consisted of nanoparticles of different size (2.6-6.9 nm) depending on the used stabilizing agent. The colloidal solutions were immobilized on activated carbon. The carbon-supported gold catalysts were used in a model reaction for the selective liquid phase oxidation of ethylene glycol to glycolate (pO(2) = 300 kPa, T = 343 K, r.t. = 1 h, [EG] = 0.5 M, EG/Au = 1000, EG/NaOH = 1, EG = ethylene glycol). A comparison of the catalytic activity underlines the importance of the stabilizing agent in both the steps of sol formation and support impregnation.