PEG-stabilized Rhodium Nanoparticles For Hydroformylation Of Olefins

Rhodium nanoparticles were prepared by the hydrogen reduction of RhCl3·3H2O in PEG 4000(polyethylene glycol, Mw= 4000), which played a role of solvent and stabilizer. TEM analysis showed that the diameter of Rh nanoparticles was 1.7±0.3 nm. XRD pattern indicated that the prepared nanoparticles were zero-valent metal. The Rh nanoparticle catalysts, used in thermoregulated PEG 4000/toluene/n-heptane biphase system, could dissolve in the PEG phase but insoluble in the organic phase at room temperature. At the reaction temperature (higher than the miscibility temperature of the system), the whole system became homogeneous and Rh nanoparticles could be well dispersed in the system to catalyze the reaction. After reaction, two phases formed again on cooling to room temperature. The upper organic phase containing the product could be easily separated from the PEG phase by simple phase separation, then the PEG phase containing Rh nanoparticle catalysts could be reused directly for the next reaction run.The Rh nanoparticles were applied to catalyze the hydroformylation of 1-octene in thermoregulated PEG 4000/toluene/n-heptane biphase system. The effects of reaction temperature, time, intial gas pressure and the molar ratio of substrate to Rh were investigated in detail. Under the optimized reaction conditions:T= 120℃, t=3 h, P= 6.0 MPa (CO/H2= 1),1-octene/Rh= 1000 (molar ratio), the conversion of 1-octene and the yield of aldehydes reached to 100%and 99%, respectively. The TOF was 330 h-1. The catalysts being recycled 20 times showed no evident loss in activity.In addition, the Rh nanoparticles were used to catalyze the hydroformylation of cyclohexene in thermoregulated PEG 4000/toluene/n-heptane biphase system. Under the optimized reaction conditions:T= 120℃, t= 5 h, P= 6.0 MPa (CO/H2= 1), cyclohexene/Rh = 1000 (molar ratio), both the conversion of cyclohexene and the yield of aldehyde were 98%. The TOF was 200 h-1. The Rh nanoparticle catalysts could be recycled 20 times without evident loss in activity.