Colloidal submicron-palladium particles stabilized with acetate

Palladium spherical particles 0.23 μm in diameter were synthesized by reducing palladium acetate with hydrazine in the presence of surfactant, with an aim of exhibiting both easy separation by filtration and easy dispersion for a catalyst. The particles in the suspension were sedimented slowly but not aggregated. The suspension showed voltammetric redox waves. The anodic wave was ascribed to the oxidation of Pd to Pd2+, whereas the cathodic one was to the reduction of the palladium acetate moiety to Pd. The current ratio of the anodic peak to the cathodic one 4:1, was close to the ratios by the partial chemical oxidation with permanganate and by the thermogravimetry, suggesting the composition of 80% palladium metal and 20% palladium acetate in the molar ratio. Heating the palladium particles at 300 °C yielded palladium metal. The decomposition proceeded to the first-order reaction with the activation energy of 40 kJ mol−1. The particle catalyzed the reduction of methylene blue with hydrazine. The reaction rate was of the first-order with respect to methylene blue. The rate constant was proportional to the geometrical surface area of the palladium particle, suggesting a surface catalysis.