表面润湿性可控的碳纳米管负载钯催化剂及其在1,8-二硝基萘选择性加氢中的催化性能

Carbon nanotubes supported palladium catalyst with wettability controllable surface and its catalytic performance in selective hydrogenation of 1,8-dinitronaphthalene

首先通过原子转移自由基聚合技术(atom transfer radical polymerization,ATRP)在碳纳米管(CNT)表面接枝聚N-异丙基丙烯酰胺(PNIPAM),成功制备出表面润湿性可控的复合载体(CNT-PNIPAM),并以其为载体制备Pd催化剂(Pd/CNT-PNIPAM)。采用红外光谱仪(FTIR)、热重仪(TGA)、有机元素分析仪(OEA)、差示量热仪(DSC)、X射线衍射仪(XRD)、透射电镜(TEM)和N2吸附等手段对材料进行表征。制备的催化剂用于1,8-二硝基萘(1,8-DNN)选择性加氢反应,并研究表面化学对催化性能的影响。结果表明,CNT-PNIPAM的最低临界溶液温度(LCST)为37℃左右。利用温敏效应,CNT-PNIPAM在25℃(LCST)下表面润湿性发生转换。PNIPAM接枝引起催化剂表面化学性质的变化,进而使其对底物的吸附性能发生改变。Pd/CNT-PNIPAM上Pd颗粒的高度分散及其对1,8-DNN优良的吸附性能不仅使催化活性得以提高(反应速率常数k=2.1h-1),而且对1,8-DAN的选择性也更高(完全反应时1,8-DAN选择性达98%)。

PNIPAM was successfully grafted on carbon nanotubes(CNT) by Atom Transfer Radical Polymerization(ATRP). The synthesized composite CNT-PNIPAM with wettability controllable surface was then used as support to prepare Pd catalyst(Pd/CNT-PNIPAM). The composite and its supported Pd catalyst were characterized by FTIR, TGA, OEA, DSC, XPS, XRD, TEM and N2 adsorption. Further, the as-prepared catalysts were applied for selective hydrogenation of 1,8-dinitronaphthalene(1,8-DNN) and the effect of surface chemistry on the catalytic performance was studied. The results showed that CNTPNIPAM had a lower critical solution temperature(LCST) about 37℃. It exhibited hydrophilic surface at room temperature that was helpful for the Pd dispersion. The Pd nanoparticles deposited had a small particle size of 3.6 nm±0.8 nm. When the temperature ascended to 120℃(>LCST), the surface wettability of Pd/CNT-PNIPAM transformed from hydrophilicity to hydrophobicity. The changes in the surface chemical properties after PNIPAM grafting further caused the changes in its adsorption performance to the substrates. Highly dispersed Pd nanoparticles on Pd/CNT-PNIPAM and its excellent adsorption performance to 1,8-DNN resulted in the enhanced catalytic activity(reaction rate constant k=2.1 h-1) and selectivity to 1,8-DAN(98% 1,8-DAN selectivity at nearly complete reaction).