氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢（英文）

发布时间：2018-04-12 20:25

本文选题：氮掺杂介孔碳材料 + 多功能载体　；参考：《催化学报》2017年07期

【摘要】：氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m~2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPaH_2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO_2,Pt/TiO_2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO_2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO_2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.
[Abstract]:Nitrogen-doped ordered mesoporous carbon materials not only have the advantages of high specific surface area, large pore volume and uniform and adjustable pore size, but also can regulate the physical and chemical properties of materials and the charge density of coordination metals.It is a kind of excellent catalyst support.In this paper, a soft template (block copolymer F127 as template, m-aminophenol as carbon source and nitrogen precursor) and a specific surface area of 417mg / g, as well as regular pore size distribution mesoporous carbon materials were prepared.The results show that the prepared material has three dimensional cubic phase structure.Using the carbon material as the carrier, the traditional impregnated hydrogen reduction strategy was used to load the platinum nanoparticles.It is found that the nitrogen-doped carrier can effectively control the size of metal nanoparticles and realize the effective loading of ultra-small Pt nanoparticles (1.0 卤0.5 nm), and the nanoparticles are uniformly distributed in the pores of mesoporous carbon materials.In contrast, under the same loading method, it is difficult to control the size of nanoparticles by using nitrogen-free mesoporous carbon materials as the carrier, and the accumulation of particles outside the channels will occur.The results show that the weak interaction between nitrogen atoms and metals in the skeleton has a stable effect on the nanoparticles.It has certain guiding significance for the preparation of ultrasmall metal nanoparticles catalyst.In addition, the size of nanoparticles will greatly affect the exposure of the catalyst active center, and then affect the activity of the catalyst.Therefore, the hydrogenation of nitrobenzene compounds was used to evaluate the catalytic performance of the catalyst.The nitrogen-doped mesoporous carbon supported catalysts exhibited excellent catalytic performance at room temperature and 1 MPaH_2.After 0.5 h reaction, p-chloronitrobenzene could be transformed completely, and the selectivity was as high as 99wt%.In contrast, the conversion and selectivity of the commercial Pt/C catalyst were 89% and 90%, respectively.The comparison of other traditional catalysts, such as PT / SiO2 / PtP / TiO2, also shows that nitrogen-doped mesoporous carbon supported catalysts have better catalytic performance.Under the same reaction conditions, only 46% conversion and 93% selectivity can be obtained for Pt- SiO2 catalyst, while Pt/TiO_2 catalyst can achieve complete conversion, but the selectivity is only 91%.It can be seen that nitrogen-doped supported catalysts can greatly improve the activity and selectivity of the reaction, and can effectively inhibit the phenomenon of dechlorination.The high catalytic performance may be related to the mesoporous structure of the catalyst, the nitrogen functionalized support and the stability of the ultrasmall Pt nanoparticles.Because of the limiting effect of nitrogen atom and mesoporous channel, the catalyst supported by nitrogen doped with mesoporous carbon also has good catalytic stability. After 10 cycles, the catalytic activity and selectivity are almost unchanged.The results showed that the size of catalyst metal particles changed little after recycling, which further indicated the stability of nitrogen-doped mesoporous carbon support on metal nanoparticles.
【作者单位】：山西大学分子科学研究所;山西大学化学化工学院;
【基金】：supported by the National Natural Science Foundation of China(201573136,U1510105) the Scientific Research Start-up Funds of Shanxi University(RSC723)~~
【分类号】：O643.36

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