Journal of Molecular Catalysis A: Chemical 298 (2009) 69–73 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata Ruthenium nanoparticles prepared from ruthenium dioxide precursor: Highly active catalyst for hydrogenation of arenes under mild conditions Liane M. Rossi a,∗ , Giovanna Machado b,c a Institute of Chemistry, Universidade de São Paulo – USP, Av. Prof. Lineu Prestes 748, São Paulo 05508-000, SP, Brazil b Institute of Chemistry, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸alves 9500, Porto Alegre 91501-970, RS, Brazil c Chemical Engineering Department, Universidade de Caxias do Sul, Rua Francisco Getúlio Vargas 1130, Caxias do Sul 95070-560, RS, Brazil article info Article history: Received 6 May 2008 Received in revised form 28 September 2008 Accepted 6 October 2008 Available online 14 October 2008 Keywords: Nanoparticle Ruthenium Hydrogenation Benzene Ionic liquid abstract The hydrogenation of benzene and benzene derivatives was studied using Ru(0) nanoparticles prepared by a very simple method based on the in situ reduction of the commercially available precursor ruthenium dioxide under mild conditions (75 ◦ C and hydrogen pressure 4atm) in imidazolium ionic liquids. Total turnovers (TTO) of 2700mol/mol Ru were obtained for the conversion of benzene to cyclohexane under solventless conditions and TTO of 1200 mol/mol Ru were observed under ionic liquid biphasic conditions. When corrected for exposed ruthenium atoms, TTO values of 7940 (solventless) and 3530 (biphasic) were calculated for benzene hydrogenation. These reaction rates are higher than those observed for Ru nanoparticles prepared from decomposition of an organometallic precursor in similar conditions. The presence of the partially hydrogenated product cyclohexene was also detected at low conversion rates. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Hydrogenation of benzene conventionally occurs under dras- tic temperature and pressure conditions over metal-supported heterogeneous catalysts, such as Rh/Al 2 O 3 or Raney nickel [1]. Recently, soluble transition metal nanoparticles stabilized in ionic liquids, polyoxoanions, quaternary ammonium salts or soluble polymers, have shown enhanced lifetime and activity in benzene hydrogenation under mild reaction conditions [2–15]. Ionic liq- uids are outstanding solvents for the synthesis and stabilization of metal nanoparticles of 2–3 nm particle size and allow easy product recovery and catalyst recycling. The catalyst-containing ionic liquid forms a biphasic reaction mixture with both sub- strate and hydrogenated products that can be easily separated by simple decantation. Hydrogenation of olefins and arenes cat- alyzed by metal nanoparticles soluble in ionic liquids has received increasing attention [3,6,11,13,15–19]. Rhodium(0), iridium(0), plat- inum(0) and ruthenium(0) nanoparticles of 2–3 nm diameter with narrow size distribution have been synthesized in 1-n-butyl-3- methylimidazolium ionic liquids by reduction with molecular hydrogen of metal complexes [6,16] or controlled decomposition of organometallic compounds [3,13] under mild reaction condi- ∗ Corresponding author. Tel.: +55 11 30912181; fax: +55 11 38155579. E-mail address: lrossi@iq.usp.br (L.M. Rossi). tions (75 ◦ C and hydrogen pressure 4atm). It is worth to mention the results of benzene hydrogenation by iridium(0) nanoparticles stabilized by ionic liquid with total turnover (TTO) of 3509 in sol- ventless mild reaction conditions (corrected for exposed atoms) [6]. The hydrogenation of benzene by rhodium(0) nanoparticles stabilized by ionic liquid under forcing conditions of 40 bar of hydrogen attained the unprecedent TTO of 20,000. However, the turnover frequency (TOF) of benzene hydrogenation by those cat- alytic systems was not higher than 250 h -1 , which necessitates long reaction times. Stabilized aqueous colloidal suspensions of metal- lic nanoparticles have also been reported as reusable catalyst for arene hydrogenation in biphasic conditions (water/hydrocarbons) [10,12,20]. More elegant is the use of ionic liquids to modulate product selectivity based on different substrates, reaction intermediates and products solubilities in the ionic liquid phase. Although the selective hydrogenation of benzene to cyclohexene seems to be a property characteristic of heterogeneous catalysts, the partially hydrogenated product cyclohexene was observed during the hydro- genation of benzene by Ru nanoparticles stabilized in ionic liquids [3]. We have previously prepared ruthenium(0) nanoparticles by reduction of the corresponding commercially available ruthenium dioxide in 1-n-butyl-3-methylimidazolium ionic liquids at 75 ◦ C and 4 atm hydrogen pressure. The resulting ruthenium(0) nanopar- ticles, characterized by XRD, TEM and XPS, are a highly active and 1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2008.10.007