Shape- and Size-Selective Preparation of Hectorite-Supported Ruthenium Nanoparticles for the Catalytic Hydrogenation of Benzene

Abstract

The cationic organometallic aqua complexes formed by hydrolysis of [(C 6 H 6 ) 2 RuCl 2 ] 2 in water, mainly [(C 6 H 6 2? , intercalate into white sodium hectorite, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in water with molecular hydrogen (50 bar, 100°C) to give a dark suspension containing a black hectorite in which large hexagonally shaped ruthenium nanoparticles (20-50 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. If the reduction with molecular hydrogen (50 bar, 100°C) is carried out in various alcohols, spherical ruthenium nanoparticles of smaller size (3-38 nm depending on the alcohol) are obtained. In alcohols other than methanol, the reduction also works without H 2 under reflux conditions, the alcohol itself being the reducing agent; the ruthenium nanoparticles obtained in this case are spherical and small (2-9 nm) but tend to aggregate to form clusters of nanoparticles. Whereas the ruthenium nanoparticles prepared by reduction of the yellow hectorite in refluxing alcohols without hydrogen pressure are almost inactive, the nanoparticles formed by hydrogen reduction catalyze the hydrogenation of benzene to give cyclohexane under mild conditions (50°C) with turnover frequencies up to 6500 catalytic cycles per hour, the best solvent being ethanol.Dedicated to Professor C. N. R. Rao, pioneer of nanocluster chemistry, on the occasion of his 75th birthday.

Highly selective low-temperature hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol catalysed by hectorite-supported ruthenium nanoparticles

“…Rutheniumsupported hectorite obtained by ion exchange has been reported by Shimazu et al using [7] for the intercalation. These materials show high catalytic activity for the hydrogenation of olefins [5] and of aromatic compounds [8,9]. The hydrogenation of furfuryl alcohol (FA) to give tetrahydrofurfuryl alcohol (THFA) is of great importance [10][11][12][13], but little information is available in this regard.…”

Selective N-cycle hydrogenation of quinolines with sodium borohydride in aqueous media catalyzed by hectorite-supported ruthenium nanoparticles

“…The reduction of transition metal salts by sodium borohydride is a common method for the preparation of metallic nanoparticles that allows a certain control of the morphology, important for activity and selectivity for catalytic applications [38]. The reaction medium (organic solvents or water) is also decisive for the morphology of the nanoparticles [29,39,40]. Figure 2 shows the TEM images of nanoRu′@hectorite obtained under different conditions: The ruthenium nanoparticles formed by sodium borohydride reduction of the precatalyst in pure water without a substrate being present is depicted in Figure 2a, while Figure 2b shows the in situ generated ruthenium nanoparticles obtained during a catalytic run in aqueous solution from the precatalyst and sodium borohydride in the presence of quinoline as the substrate.…”

“…In our previous work, we developed a heterogeneous catalyst by intercalation of cationic benzene ruthenium complexes into hectorite, followed by reduction with molecular hydrogen to give a black solid containing metallic ruthenium nanoparticles intercalated in hectorite (nanoRu@hectorite) [27][28][29]. This material was found to catalyze the hydrogenation of quinoline with switchable selectivity, the reaction in water at 60 °C and 30 bar H 2 giving THQ, conversion and selectivity being at 99% [30].…”

Ruthenium Nanoparticles Intercalated in Montmorillonite (nano-Ru@MMT) Is Highly Efficient Catalyst for the Selective Hydrogenation of 2-Furaldehyde in Benign Aqueous Medium

“…Nanoparticles with controllable chemical and physical properties can conveniently be obtained by employing suitable organometallic precursors [24]. We have previously shown that the selectivity during catalytic hydrogenation reactions can be conveniently controlled with nano ruthenium, which was obtained from arene ruthenium complexes devoid of interfering chloride ions [21,[25][26][27][28][29][30][31]. In this work, dicationic aqua complex [Me(C6H4)Pr i )Ru(H2O)3] 2+ was used as a precursor to avoid the presence of contaminants on the surface of nanoparticles.…”