Recyclable nanocellulose-confined palladium nanoparticles with enhanced room-temperature catalytic activity and chemoselectivity

纳米纤维素限域钯纳米颗粒的室温催化活性及化学选择性

We describe the synthesis of even-dispersed palladium nanoparticles(Pd NPs)confined within a cellulose nanofiber(CNF)matrix for developing a high-performance and recyclable catalyst.The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam.Ultrafine Pd NPs(∼6 nm)with high-loading(9.6 wt%)were in situ grown on these mesoporous nanosheets,and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants.Consequently,the CNF-confined Pd NPs(CNF-Pd)exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate constant of 8.8×10^−3 s^−1 and turnover frequency of 2640 h The CNF Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity.Moreover,chemoselective reduction of 3 nitrostyrene was achieved with high yield(80%–98%)of 3-aminostyrene in alcohol/water cosolvent.Overall,this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts.

本文利用水合低共熔溶剂结合超声法制备了羧基化纤维素纳米纤丝(CNF),并利用其表面的羧基官能团为反应活性位点原位合成了具有均匀分散性和高负载量(9.6 wt%)的CNF-Pd复合催化剂.研究结果表明:CNF-Pd具有显著的限域特性,包括在CNF表面羧基官能团上原位固定生长Pd纳米颗粒的化学限域和CNF冷冻干燥过程中自组装形成的空间结构限域.CNF-Pd在4-硝基苯酚加氢模型反应中表现出优异的室温催化活性,其最高速率常数为8.8×10^-3s^-1,最高催化活性的转化频率为2640 h^-1.CNF-Pd催化剂在水性介质中显示出良好的化学稳定性和可回收性,至少重复使用6个循环不会失活.此外,CNF-Pd催化剂还可实现3-硝基苯乙烯在醇/水共溶剂中向3-氨基苯乙烯的化学选择性加氢,且具有80%–98%的高选择性产率.综合上述结果,CNF在构建具有高室温催化活性及可回收利用的金属纳米颗粒催化剂方面具有广泛应用潜力和发展空间.