The Partial Hydrogenation of Benzene to Cyclohexene by Nanoscale Ruthenium Catalysts in Imidazolium Ionic Liquids

摘要

The controlled decomposition of an Ru~0 organometallic precursor dispersed in l-/7-butyl-3-meth-ylimidazolium hexafluorophosphate (BMI(centre dot)PF_6),tetrafluoroborate (BMI-BF_4)or trifluoromethane sulfonate (BMI(centre dot)CF_3SO_3)ionic liquids with H_2 represents a simple and efficient method for the generation of Ru~0 nanoparticles.TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approx=57 nm that contain dispersed Ru~0 nanoparticles with diameters of 2.6+-0.4nm.These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogena-tion of alkenes and benzene under mild reaction conditions (4 atm,75 deg C).The ternary diagram (benzene/cyclo-hexene/BMI(centre dot)PF_6)indicated a maximum of 1 % Cyclohexene concentration in BMI(centre dot)PF_6,which is attained with 4% benzene in the ionic phase.This solubility difference in the ionic liquid can be used for the extraction of cyclo-hexene during benzene hydrogenation by Ru catalysts suspended in BMI(centre dot)PF_6.Selectivities of up to 39% in cyclo-hexene can be attained at very low benzene conversion.Although the maximum yield of 2% in Cyclohexene is too low for technical applications,it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles.