Abstract

[ChallengerII (狂風暴雨前的序曲)]

                                 Seminar
    Subject: Effect of Catalysis on the Stability of Metallic Nanoparticles:
Suzuki Reaction Catalyzed by PVP-Palladium Nanoparticles.
    Authors: Radha Narayanan and Mostafa A. El-Sayed*.
    Source: J. Am. Chem. Soc. 2003, 125, 8340-8347.
    Speaker: B89203014 化學四 王大明
    Date: 10 / 28 / 2003
    Abstract: The small size of nanoparticles makes them attractive in
catalysis due to their large surface-to-volume ratio. However, being small
raises questions about their stability in the harsh chemical environment in
which these nanoparticles find themselves during their catalytic function.
In this paper, the author studied the Suzuki reaction between phenylboronic
acid and iodobenzene catalyzed by PVP-Pd nanoparticles to investigate the
effect of catalysis, recycling, and the different individual chemicals on the
stability and catalytic activity of the nanoparticles during this harsh
reaction. Refluxing the nanoparticles for 12 h during the Suzuki catalytic
reaction increases the average size and the width of the nanoparticles. After
the second cycle of the reaction, the average size decreases due to the larger
nanoparticles aggregating and precipitating out of solution. Biphenyl product
results in poisoning the active sites and giving rise to a low product yield.
Excess PVP stabilizer seems to stabilize the nanoparticle surface and size but
also decrease the catalytic efficiency of the nanoparticles due to capping of
the nanoparticle surface. Phenylboronic acid leads to the stability of the size
distribution as it binds to the particle surface through the O- of the OH group
and acts as a stabilizer. Iodobenzene is found to have no effect and thus
probably does not bind strongly to the surface during the catalytic process.
These two results might have an implication on the catalytic mechanism of this
reaction
     References:
     (1) Teranishi, T.; Miyake, M. Chem. Mater. 1998, 10, 594-600
     (2) Li, Y.; Hong, X. M.; Collard, D. M.; El-Sayed, M. A. Org. Lett. 2000,
 2, 2385.
     (3) Li, Y.; Boone, E.; El-Sayed, M. A. Langmuir 2002, 18, 4921.
     (4) Howard, A.; Mitchell, C. E. J.; Egdell, R. G. Surf. Sci. 2002, 515,
L504.
     (5). Roucox, A:, Sculz, J.; Patin, H. Chem. Rev. 2002, 102, 3757.

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