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Platinum, palladium and rhodium nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) can be synthesized by ethanolic reduction of the corresponding metal halide salts and when immobilized in an ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]), are very effective olefin hydrogenation catalysts which are capable of being recycled by a simple decantation procedure without loss of activity. [ABSTRACT FROM AUTHOR]

This article focuses on the stabilization of rhodium nanoparticles by ionic copolymers in ionic liquids. Metallic nanoparticles are kinetically unstable with respect to agglomeration to the bulk metal and must therefore be stabilized by additives, examples include quarternary ammonium salts, soluble polymers, and polyoxoanions. Combining different stabilizing effects in nanoparticles, may produce stable and active nanoparticles. For example, rhodium nanoparticles co-stabilized with polyoxoanions and tetrabutylammonium cations can give total turnovers (TTO) up to 193,000 for olefin hydrogenation and a TTO of 2600 for arene hydrogenation. Recently, nanoparticles stabilized by an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, have been reported, and a TTO of 3509 in 32 h for arene hydrogenation by iridium has been achieved. More recent studies have shown that imidazolium ILs may oxidatively add to coordinatively unsaturated low valent metal centers, implying that the ILs might stabilize metal nanoparticles not only electrostatically but also by coordination involving the cations.