催化学报 ›› 2019, Vol. 40 ›› Issue (10): 1557-1565.DOI: 10.1016/S1872-2067(19)63416-9

• 论文 • 上一篇    下一篇

纤维素原位合成Fe-N-C催化加氢硝基苯到苯胺

王昊a, 刘小好a, 许光月a, 郭子薇a, 张颖a,b   

  1. a 中国科学技术大学化学与材料科学学院化学系, 安徽合肥 230026;
    b 中国科学院洁净能源创新研究院, 辽宁大连 116023
  • 收稿日期:2019-04-28 修回日期:2019-05-27 出版日期:2019-10-18 发布日期:2019-08-26
  • 通讯作者: 张颖
  • 基金资助:
    国家自然科学基金(51876200,21572213);中国科学院洁净能源创新研究院合作基金(DNL180301).

In situ synthesis of Fe-N-C catalysts from cellulose for hydrogenation of nitrobenzene to aniline

Hao Wanga, Xiaohao Liua, Guangyue Xua, Ziwei Guoa, Ying Zhanga,b   

  1. a Department of Chemistry, University of Science and Technology of China, Hefei 230026, Anhui, China;
    b Dalian National Laboratory for Clean Energy, Dalian 116023, Liaoning, China
  • Received:2019-04-28 Revised:2019-05-27 Online:2019-10-18 Published:2019-08-26
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (51876200, 21572213), and the DNL Cooperation Fund, CAS (DNL180301).

摘要: 贵金属被广泛用作各种反应的催化剂,然而它们高昂的价格和有限的来源引起了人们对于开发非贵金属催化剂的浓厚兴趣.因此,寻找一种丰富而有效的催化剂来代替贵金属已成为催化领域最重要的任务之一.铁是地球上最丰富、最廉价的过渡金属,同时铁基催化剂在合成氨,费托合成和选择性还原氮氧化物等方面表现出优异的活性.近年来,廉价高效的氮掺杂碳负载铁催化剂在各种典型的铂催化反应中表现出良好的催化性能,尤其在催化加氢反应中的应用引起了研究人员的关注.本文通过在氨气氛围下共热解纤维素和氯化铁制备了一系列氮掺杂碳负载铁催化剂,并通过元素分析、原子吸收光谱、透射电子显微镜、X射线衍射和X射线光电子能谱等表征方法,探索了催化剂的物理化学性质.同时以硝基苯加氢制备苯胺为模型反应,探究了催化剂制备条件和反应条件对于催化剂活性的影响.其中Fe-N-C-700(通过在氨气氛围下700℃共热解纤维素和氯化铁制备)表现出最佳活性,在5 MPa氢气和120℃的条件下反应12 h,硝基苯被完全转化,苯胺的收率可达98.0%,同时,该催化剂还显示出良好的可再循环性,5次运行后未见催化活性的显著降低.
BET和元素分析结果表明,在热解温度为700℃的条件下制备的催化剂具有最高的比表面积,并且随着热解温度的升高,催化剂中碳元素和铁元素的含量升高,而氢、氮、氧元素的含量都随之下降.根据TEM图像,当热解温度升至600℃时,在碳材料上可以观察到平均尺寸为5.1 nm的金属颗粒,分散性较好.进一步将温度升至700℃,观察到平均尺寸为9.1 nm的金属颗粒,并且碳材料的形态结构转变为卷曲的层状.在XRD分析中,600℃时催化剂的衍射峰归因于正交晶系的Fe2N,随着温度升至700℃,Fe2N相消失同时出现了Fe3C相.在HRTEM的图谱中,可以清晰地看到Fe3C相的(031)面的衍射条纹,并且在颗粒周围有约5.2 nm厚的石墨碳层包裹.XPS结果表明,当温度达到700℃时,形成石墨化的氮掺杂碳,提高了催化剂活性.结合催化剂表征结果和对比实验,催化剂中铁物种的转变和氮掺杂碳尤其是石墨化的氮掺杂碳的生成可能是影响催化剂活性的主要因素.根据动力学实验,当使用Fe-N-C-700催化剂时,硝基苯加氢反应表观活化能为31.53 kJ/mol(报道为91.5 kJ/mol),这表明Fe-N-C-700催化剂可以有效地降低反应活化能.

关键词: 共热解, 铁, 氮掺杂, 碳材料, 氢化反应

Abstract: Owing to Fe being the most abundant and least expensive transition metal on the earth, the utilization of Fe-based catalysts for catalytic hydrogenation has attracted worldwide attention. In this work, a series of N-doped C supported Fe catalysts (Fe-N-C) were prepared by co-pyrolysis of cellulose and ferric chloride under ammonia atmosphere. Characterization methods such as elemental analysis, atomic absorption spectroscopy, nitrogen adsorption-desorption isotherms, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out to explore the physicochemical properties of the catalysts. Using hydrogenation of nitrobenzene as a model reaction, the catalysts prepared at different pyrolysis temperatures displayed different activities. Fe-N-C-700 exhibited the best activity among these catalysts, with the yield of aniline being up to 98.0% under 5 MPa H2 at 120℃ after 12 h. Combined with the results of catalyst characterization and comparative tests, the transformation of Fe species and the generation of N-doped C, especially graphitized N-doped C, in the catalyst may be the main factors affecting the activity. A kinetic study was carried out and the apparent activation energy was obtained as 31.53 kJ/mol. The stability of the catalyst was also tested and no significant decrease in the activity was observed after 5 runs.

Key words: Co-pyrolysis, Iron, Nitrogen-doped, Carbon, Hydrogenation