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Laboratorio de Filmes Finos e Fabricação de Nanoestruturas (L3FNano), Institute of Physics, UFRGS Avenida Bento Gonçalves, 9500 Porto Alegre 91501-970 RS, Brazil
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Phys. Chem. Chem. Phys., 2010,12, 6826-6833
08 Dec 2009,
10 Mar 2010
First published online
07 May 2010
Hydrogenreduction of cationic or neutral Ir(I) compounds, namely [Ir(COD)2]BF4 and [Ir(COD)Cl]2respectively. in the ionic liquid (IL) 1-alkyl-3-methylimidazolium tetrafluoroborate affords either irregularly sized spherical (from 1.9 ± 0.4 to 3.6 ± 0.9 nm) or worm-like metal nanoparticles, depending on the nature of the imidazolium alkyl group and the type of iridium precursor. The ionic Ir(I) precursor tends to be dissolved and concentrated on the IL polar domains (populated by the imidazoliumnucleus and tetrafluoroborate anions) while the neutral precursor dissolves preferentially in the non-polar region of the IL (populated mainly by N-alkyl side chains). The size, or volume, of the nano-region where the Ir(I) precursor is dissolved and reduced, determines the size and, probably, the shape of the formed nanoparticles. The HR-TEM image shows that the Ir(0) with worm-like shape are polycrystalline and formed from aggregation individual “spherical” nanoparticles of around 1.9 nm. The catalytic activity of Ir(0) NPs on the hydrogenation of cyclohexene (0.01 mol L−1 of Ir atoms in IL, 75 °C, 8 bar of H2, 500 rpm stirring, 1/1000 Ir(0)/cyclohexene ratio) is always greater in C1C10I·BF4 than C1C4I·BF4, regardless of the nature of Ir(I) precursor. Moreover, the cyclohexene hydrogenations performed with Ir(0) nanocatalysts made from ionic Ir(I) precursor are approximately twice faster than those NPs obtained from the neutral Ir(I) precursor, in the same IL.
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