Synthesis, characterization, and highly efficient catalytic reactivity of suspended palladium nanoparticles

The catalytic activities of suspended nano-sized palladium catalysts toward various olefin hydrogenation reactions are reported. The Pd nanoparticles were prepared by a laser ablation method followed by careful characterization. Two types of Pd nanoparticle systems were fabricated and subjected to a series of catalytic activity measurements: (i) Pd nanoparticles stabilized by tetraoctylammonium bromide (TC(8)ABr) ionic micelles with an average diameter of 2.4 +/- 0.5 nm and (ii) bare-Pd nanoparticles with an average size of 12.7 +/- 5.7 nm in diameter. The catalytic activities of both TC(8)ABr-Pd and bare-Pd nanoparticles were examined by measuring their turnover numbers (TON) in several target olefin hydrogenation reactions, such as the transformations of styrene to ethylbenezene, 2-methyl-2-butene to 2-methylbutane, 1-octene to n-octane, trans-stilbene to bibenzyl, and cyclohexene to cyclohexane. Data are compared to the hydrogenation results using a commercially available Pd/C catalyst system under similar reaction conditions. An exclusive selectivity of the catalytic styrene hydrogenation reaction on the C=C bond, rather than on the aromatic ring, was found among three systems, giving ethylbenzene as the only product. The catalyst stability was found to be on the order of TC(8)ABr-Pd > bare-Pd > 10% Pd/C. (C) 2000 Academic Press.