Redox Catalytic Property of Still-Growing and Final Palladium Particles: A Comparative Study

The redox catalytic property of still-growing and final particles of palladium has been investigated using methylene blue (MB) and fluorescein (F) as redox probes. Reductions of MB by N 2 H 4 and of F by NaBH 4 were observed to be catalyzed by both the still-growing and the final Pd particles. In most cases the catalytic rate increases exponentially with the increase in catalyst precursor ion concentration, that is, [Pd II ] and [N 2 H 4 /NaBH 4 ]. However, with the increase in [dye], the rate decreases in most cases, and this effect is more prominent for still-growing particles than final particles. The study shows that particle size has a significant role in influencing the catalytic property of the metal. Still-growing particles are smaller in size and render more catalytic activity provided they are sufficiently stable and their surface is not poisoned by the chemisorption of reactants or any other foreign ions/molecules. Palladized charcoal has been observed to be a much weaker catalyst than the two studied here because of its larger particle size and carbon-covered surface. An ion-exchange mechanism is proposed to explain the catalytic rate. The dye and the reducing agent are in equilibrium between the catalyst surface and bulk water. Thus, the rate of dye reduction depends on the surface concentration of dye and reducing agent.