Carbon-supported spherical palladium nanoparticles as potential recyclable catalysts for the Suzuki reaction

Carbon-supported PVP-Pd nanoparticles prepared by adsorption of colloidal PVP-Pd nanoparticles onto activated carbon are used as catalysts for the Suzuki reaction between phenylboronic acid and iodobenzene to form biphenyl. These carbon-supported nanoparticles result in a lower biphenyl yield during the first cycle than the colloidal Pd nanoparticles that we studied previously. The carbon-supported Pd nanoparticles retain 69% of its activity upon recycling (second cycle), which is almost double the recycling potential observed in colloidal Pd nanoparticles (37% retention of activity). In addition, the carbon-supported Pd nanoparticles retain 73 +/- 3% of their catalytic activity during the second through fifth cycles of the Suzuki reaction, while the catalytic activity of the colloidal Pd nanoparticles greatly decreases during that time frame. The carbon support that the palladium nanoparticles are adsorbed onto helps to preserve its catalytic activity for longer time periods. The effect of catalysis and recycling on the nanoparticle size is also investigated. The average size of the carbon-supported palladium nanoparticles is 1.9 +/- 0.1 nm initially, 2.6 +/- 0.1 nm after the first cycle, and 3.1 +/- 0.1 nm after the second cycle. The continued growth of the supported nanoparticles suggests that the carbon support protects the palladium nanoparticles during the harsh Suzuki reaction and prevents aggregation and precipitation unlike the colloidal palladium nanoparticles. In addition, a narrow size distribution during the growth process (Ostwald ripening) is observed for the carbon-supported nanoparticles. This could be due to the adsorption method for preparing carbon-supported Pd nanoparticles because excess unaggregated palladium atoms will not be adsorbed onto the carbon support. (c) 2005 Elsevier Inc. All rights reserved.