Iridium@graphene composite nanomaterials synthesized in ionic liquid as re-usable catalysts for solvent-free hydrogenation of benzene and cyclohexene

• Easy iridium nanoparticle synthesis and deposition on graphene in ionic liquids (ILs).
• Rapid synthesis by microwave or electron-beam irradiation of Ir-carbonyl in ILs.
• Ir-nanoparticles on graphene as stable, re-usable hydrogenation catalyst.
• Synthesis and catalytic use of stable 2–5 nm Ir-nanoparticles on graphene.
• Hydrogenation catalysis under solvent-free conditions with easy catalyst recycling.

Synthesis of stable hybrid iridium@graphene nanomaterials in the ionic liquid (IL) 1-butyl-3-methyl-imidazolium tetrafluoroborate ([BMIm][BF4] through microwave irradiation (MWI) or electron-beam (e-beam) irradiation (IBA Rhodotron accelerator) induced decomposition of Ir4(CO)12 in the presence of graphene provides an easy method for the generation of small iridium nanoparticles with size distributions of 1.0 ± 0.4 and 2.7 ± 0.7 nm by MWI reactions with 90 and 60 min decomposition time, respectively, and of 3.6 ± 1.0 nm for e-beam irradiation synthesis. Graphene was derived by thermal reduction of graphite oxide (TRGO). Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) showed the formation of Ir nanoparticles which are evenly distributed on the TRGO sheets. Ir@TRGO proved to be a highly active (∼10 000 mol cyclohexane x(mol Ir)−1x h−1 for benzene hydrogenation) and selective heterogeneous catalyst for the industrially relevant hydrogenation of benzene or cyclohexene to cyclohexane under mild conditions (100 °C, 10 bar H2) with quantitative conversion. The catalyst could be re-used over 10 consecutive hydrogenation reactions with similar activities. A brief correlation between activity and particle size points to an optimal diameter or surface regime for the catalytic activity with iridium particles of 3.6 ± 1.0 nm on TRGO giving here the highest activity in benzene hydrogenation.

Figure optionsDownload as PowerPoint slide