Redox catalytic property of still-growing and final palladium particles: Acomparative study

The redox catalytic property of still-growing and final particles of pallad ium has been investigated using methylene blue (MB) and fluorescein (F) as redox probes. Reductions of MB by N2H4 and of F by NaBH4 were observed to b e catalyzed by both the still-growing and the final Pd particles. In most c ases the catalytic rate increases exponentially with the increase in cataly st precursor ion concentration, that is, [Pd-II] and [N2H4/NaBH4]. However, with the increase in [dye], the rate decreases in most cases, and this eff ect is more prominent for still-growing particles than final particles. The study shows that particle size has a significant role in influencing the c atalytic property of the metal. Still-growing particles are smaller in size and render more catalytic activity provided they are sufficiently stable a nd their surface is not poisoned by the chemisorption of reactants or any o ther foreign ions/molecules. Palladized charcoal has been observed to be a much weaker catalyst than the two studied here because of its larger partic le size and carbon-covered surface. An ion-exchange mechanism is proposed t o explain the catalytic rate. The dye and the reducing agent are in equilib rium between the catalyst surface and bulk water. Thus, the rate of dye red uction depends on the surface concentration of dye and reducing agent.