Palladium-Zinc catalysts on mesoporous titania prepared by colloid synthesis. I. size control synthesis of PdZn nanoclusters by a polyol method

摘要

Monodispersed Pd and PdZn bimetallic colloidal particles have been prepared by an ethylene glycol reduction of ZnCl _2 and/or Pd(CH _3COO) _2 in the presence of polyvinylpyrrolidone (PVP). The optimization of synthesis procedure of colloidal PdZn bimetallic nanoparticles have been done with variation of molar ratio of metals, the molar ratio of protecting agent to the metal, precursors and NaOH concentration. The nanoparticles in the "as prepared" state and after purification from stabilizer were characterized by TEM, SAXS, XRD, EDS, and XPS permitting determination of their mean particle size, composition and electronic state. The particle size control required for structure sensitive reaction was achieved by varying PVP/Me molar ratio, precursors and NaOH concentrations. Bimetallic colloidal PdZn particles can be prepared within the range of 1.8-4.3 nm. The bulk composition of nanoparticles depends on concentrations of the precursors and NaOH. The reaction mechanism is shown to involve the oxidation of ethylene glycol to mainly glyoxal and glycolic acid, while the metal Pd salts are reduced to form catalysts for Zn ~(2+) ions reduction.