New Au(0) sols as precursors for heterogeneous liquid-phase oxidation catalysts

New Au(0) sols were obtained by reducing antic compounds (AuCl3, NaAuC4, and HAuCl4)with reducing compounds (H2C2O4, SnCl2, and NaBH4) in the presence of protective agents [polyvinylalcohol, PVA, and poly(diallyldimethylammonium chloride), PDDA] in aqueous solutions. The sols, characterized by TEM microscopy and UV-visible spectroscopy, consisted of nanoparticles of different sizes depending on the preparation method. The colloidal solutions were immobilized on activated carbon and titania. The obtained heterogeneous catalysts were tested in 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 using the correct sol with respect to the support. (C) 2002 Elsevier Science (USA).