Kinetic Studies on Nanocatalysis by Iridium Nanoclusters in Some Oxidation Reactions

Abstract

The use of a catalyst is a common way to minimize energy use and less material waste formation by lowering the energy of activation for a reaction. With catalysts reactions can be more efficient and selective. This provides an enormous energy savings while reducing the risks of explosion or other high temperature hazards. The field of nanocatalysis has undergone an explosive growth during the past decades, both in homogeneous and heterogeneous catalysis. Since nanoparticles have a large surface-to-volume ratio compared to bulk materials, they are attractive to use as catalysts. With the improved developments in nano-chemistry, it is now possible to prepare soluble analogues of heterogeneous catalysts, materials that might have properties intermediate between those of the bulk metal and single metal-particle (homogeneous) catalysts. Noble metal nanoparticles with high specific catalytic activity are ubiquitous in modern synthetic organic chemistry during the recent decades. However how to reduce their dosage is one of the most exiting challenges due to the limited reserves of noble metals. In this study colloidal dispersion of iridium nanoparticles have been synthesized by wet reduction method using different polymers as protecting agent after the reduction of precursor salt by alcohol. The particle size has been effectively controlled in the range of 10 nm by the variation of solvent, reductant, temperature and polymer concentration. The synthesized iridium nanoparticles were characterized by UV-vis, XRD, FT-IR, TEM etc technique. The catalytic activity of colloidal iridium nanoparticles was evaluated in some oxidation reactions like amino acids- hexacyanoferrate (III) redox system in alkaline medium. These nanoparticles show a better catalytic activity than an equal amount of iridium precursor. Easy recovery of the catalyst from the reaction mixture shows another positive significance. Superior catalytic activities of nanoparticle-based catalytic systems than the corresponding bulk materials and recycling of metal nano particles are helpful in reducing the raw material costs and engineering a greener process via limiting the amount of waste chemicals for disposal.