A colloidal system based on an aqueous suspension of rhodium(0) nanoparticles proved to be an efficient catalyst for the hydrogenation of arene derivatives under biphasic conditions. The rhodium nanoparticles (2 ± 2.5 nm) were synthesized by the reduction of RhCl 3´3 H 2 O with sodium borohydride and were stabilized by highly watersoluble N-alkyl-N-(2-hydroxyethyl)ammonium salts (HEA-C n ). These surfactant molecules were characterized by measurements of the surface tension and the aqueous dispersions with rhodium were observed by transmission electron cryomicroscopy. The catalytic system is efficient under ultramild conditions, namely room temperature and 1 atm H 2 pressure. The aqueous phase which contains the protected rhodium(0) colloids can be reused without significant loss of activity. The microheterogeneous behavior of this catalytic system was confirmed on a mercury poisoning experiment.

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International audienceThe total oxidation of toluene was carried out in a series of catalytic systems composed of either palladium or gold, as active phase, with hydroxyapatite as supports. The influence of different parameters on the catalytic reactivity was investigated: the type of support, the active phase content, the preparation method, and the nature of the active phase. Hydroxyapatite supports, impregnated by the active phase, showed better reactivities than that of the classical alumina one. Moreover, low palladium content (0.25 wt%) is enough to get high toluene conversions at low temperatures. Two preparation methods were used to introduce the active phase on the support: the conventional wet impregnation and the nanoparticle deposition achieved by impregnation of a colloidal suspension of the noble metal using the surfactant HEA16Cl. Introducing palladium by either of these methods leads to similar catalytic efficiencies. In addition to this, palladium is much more active than gold, gold was not probably present under the form of highly dispersed nanoparticles. X-ray Photoelectron Spectroscopy (XPS) evidenced PdO presence on the surface of all our catalysts. Palladium impregnated on apatite by conventional method showed an improvement of catalytic reactivity after 13 h under reacting mixture, probably because of Pd(0) formation besides PdO. As a result and after a literature survey, our catalysts could be classified among the most reactive systems towards total oxidation of toluen

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