Thermoregulated Phase-Transfer Property Of Rhodium Nanoparticle Catalyst And Its Applications

Soluble transition-metal nanoparticles in catalysis have drawn much attention due to their high efficiency and selectivity. However, very similar to traditional homogeneous catalysts, one of the main disadvantages of soluble nanoparticle catalysts is the problem of separation the catalyst from the products. In this paper, rhodium nanoparticles stabilized by thermoregulated ligand Ph2P(CH2CH2O)nCH3(n= 16)(L) were prepared by hydrogenation reduction. The rhodium nanoparticle catalyst stabilized by thermoregulated ligand L exhibited the thermoregulated phase-transfer property in the aqueous/1-butanol biphasic system, That is to say, the rhodium nanoparticle catalyst was in the lower water phase at room temperature, afterwards, when the temperature heated to 60℃, the rhodium nanoparticle catalyst transferred from the water phase into the upper 1-butanol phase, after cooling to room temperature, the rhodium nanoparticle catalyst could go back to the lower water phase from the upper 1-butanol phase.The thermoregulated phase-transfer property of rhodium nanoparticle catalyst stabilized by thermoregulated ligand L in the aqueous/1-butanol biphasic system and its catalytic effect on the hydrogenation, hydroformylation and hydroaminomethylation of higher olefins were investigated.The thermoregulated phase-transfer rhodium nanoparticle catalyst was used to catalyze hydrogenation of olefins. The catalytic activity and recycling efficiency of the catalyst were studied in detail. For the hydrogenation of cyclohexene catalyzed by the thermoregulated phase-transfer rhodium nanoparticle catalyst in the aqueous/1-butanol biphasic system, under the conditions of P/Rh= 2(molar ratio), S/Rh= 1000(molar ratio), T=60℃, PH2= 1 MPa and t= 1 h, the conversion of cyclohexene reached up to 100%and the TOF was 1000 h-1. Catalytic activity remained unchanged within six successive runs. The average leaching of rhodium to the product phase was 0.2 wt.%.We extended the application of the thermoregulated phase-transfer rhodium nanoparticle catalyst to the hydroformylation of higher olefins. Under the conditions of T= 70℃, P/Rh= 13(molar ratio), S/Rh=1000(molar ratio), P= 5 MPa(CO/H2= 1:1), t= 6 h, the conversion of 1-octene and yield of aldehyde were 98% and 96%, respectively. The catalyst could be easily separated from product by phase separation and used for three times without evident loss in activity.Rhodium nanoparticle catalyst was used to catalyze hydroaminomethylation of higher olefins for the first time. For the hydroaminomethylation of 1-octene, under the conditions of T = 120℃, S/Rh= 1000(molar ratio), P/Rh= 2(molar ratio), P= 6 MPa (CO/H2=1:1), t= 4 h, the conversion of 1-octene and the selectivity for amine were up to 99% and 97%, respectively. Moreover, the catalyst could be recycled at least three runs.In summary, the methodology of TRPTC of nanoparticle catalysis system is simple to realize and the catalyst is easy to separate from the product and recycle. Therefore, it opens up a new avenue for recovery and recycling of soluble transition-metal nanoparticle catalyst.