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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.
Nitrogen-doped ordered mesoporous carbon materials not only have the advantages of high specific surface area, large pore volume and uniformly adjustable pore size, but also the abundant nitrogen atoms in the framework can also be used for the physicochemical properties of the material, the coordination metal charge density Etc., a kind of excellent catalyst carrier was prepared.In this paper, a high content of nitrogen (9.58 wt%) was prepared by using soft template (block copolymer F127 as a template), m-aminophenol as carbon source and nitrogen precursor, And the specific surface area (417 m ~ 2 / g), as well as the regular pore size distribution of the mesoporous carbon material.The results show that the prepared material has a three-dimensional cubic phase structure of the carbon material as a carrier, using conventional impregnated hydrogen reduction strategy load nano It was found that the nitrogen-doped carrier can effectively control the size of the metal nanoparticles, and the effective load (1.0 ± 0.5 nm) of the ultra-small Pt nanoparticles can be achieved, and the nanoparticles are uniformly distributed in the mesoporous carbon channels. In contrast, with the same loading method, the size of nanoparticle is more difficult to control (4.4 ± 1.7 nm) and the aggregation of extra-granular particles will occur due to the non-doped mesoporous carbon material. , Nitrogen in the skeleton The weak interaction with metal has a stabilizing effect on the nanoparticles, which is of guiding significance for the preparation of ultra-small size metal nanoparticles. In addition, the size of the nanoparticles will greatly affect the exposure of the active site of the catalyst, Therefore, we evaluated the catalytic performance of nitrobenzenes by hydrogenation.The nitrogen-doped mesoporous carbon supported catalysts exhibited excellent catalytic performance under room temperature and mild conditions of 1 MPaH 2. For 0.5 h, para-chloronitrobenzene was completely converted with a selectivity of up to 99%, compared with 89% and 90% for the commercial Pt / C catalyst, respectively.Other traditions Comparison of catalysts, such as Pt / SiO_2, Pt / TiO_2, also showed that the catalyst with more nitrogen-doped mesoporous carbon had more excellent catalytic performance.Under the same reaction conditions, the conversion of Pt / SiO_2 catalyst was only 46% And 93%, respectively, while the Pt / TiO 2 catalyst can achieve complete conversion, but the selectivity is only 91%. Thus, the nitrogen-doped supported catalyst can greatly improve the reactivity and selectivity, can effectively Dechlorination phenomenon occurs.The high catalytic performance may be related to the catalyst mesoporous structure, nitrogen functionalized support and the stability of ultra-small size Pt nanoparticles due to the limited role of nitrogen atoms and mesoporous channels, nitrogen-doped The mesoporous carbon supported catalysts also showed good catalytic stability with almost no reduction in the catalytic activity and selectivity after 10 cycles.The results showed that the size of the catalyst metal particles did not change much after the recycling and further showed that nitrogen doping The stabilizing effect of mesoporous carbon on metal nanoparticles.