A simple and reproducible method for the synthesis of silica-supported rhodium nanoparticles and their investigation in the hydrogenation of aromatic compounds

Colloidal suspensions of rhodium nanoparticles have been easily prepared in aqueous solution by chemical reduction of the precursor RhCl3 center dot 3H(2)O in the presence of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (HEA16Cl) and further used to immobilize rhodium nanoparticles on silica by simple impregnation. The obtained silica-supported rhodium nanoparticles have been investigated by adapted characterization methods such as transmission electron microscopy and X-ray photoelectron spectroscopy. A particle size increase from 2.4 to 5 nm after the silica immobilization step and total elimination of the surfactant has been observed. This heterogeneous catalyst displayed good activities for the hydrogenation of mono-, dialkylsubstituted and/or functionalized aromatic derivatives in water under atmospheric hydrogen pressure and at room temperature. In all cases, the catalyst could be recovered several times after a simple decantation or filtration and reused without any significant loss in catalytic activity. This supported catalyst has also been tested under higher hydrogen pressure giving rise to TOFs reaching 6430 h(-1) at 30 bar and in terms of catalytic lifetime 30 000 TTO in 8.5 h for pure anisole hydrogenation at 40 bar.