| In recent years,soluble transition metal nanocatalysts have attracted the attention of researchers due to their superior catalytic performance.However,separation and recycle of the expensive catalyst is still a difficult problem.Based on the previous study of our group,in this paper,the Pd nanocatalyst was successfully prepared by the reduction of Na2PdCl4·xH2O with hydrogen using thermoregulated ligand Ph2P?CH2CH2O?22CH3?L?as the stabilizer,and the average diameter of newly prepared Pd nanocatalyst was 3.0±0.3 nm.The thermoregulated phase-transfer of Pd nanocatalyst in water/1-pentanol biphasic system was realized,and the phase transfer temperature was 51?.The thermoregulated phase-transfer Pd nanocatalyst was applied to the selective hydrogenation of 1,5-cyclooctadiene?1,5-COD?at atmospheric hydrogen pressure,and the reaction conditions were systematically investigated.Under the optimized conditions?1 bar H2,L/Pd=16?molar ratio?,T=80?,t=60 min,1,5-COD/Pd=1500?molar ratio??,the conversion of 1,5-COD and the selectivity to cyclooctene?COE?was>99%and 95%,respectively.The turnover frequency?TOF?of 1411 h-11 is the highest value ever reported among Pd nanocatalysts for this reaction at atmospheric hydrogen pressure.In the recycling experiments,the Pd nanocatalyst can be simply separated from products and directly reused three times without any further treatment,only a slight decrease of conversion and selectivity were observed in the third cycle.The average leaching of Pd in 1-pentanol was 0.72%?wt.%?,and the particle size of Pd nanocatalyst after two cycles was slightly increased?4.2±0.5 nm?compared with the newly prepared Pd nanocatalyst?3.0±0.3 nm?.What's more,the turnover number?TON?of the reaction was 4077,which is the highest value ever reported among Pd nanocatalysts for this reaction at atmospheric hydrogen pressure.Mercury poisoning experiments indicated that the Pd nanocatalyst might be heterogeneous in this process. |
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