催化学报 ›› 2017, Vol. 38 ›› Issue (3): 537-544.DOI: 10.1016/S1872-2067(17)62761-X

• 论文 • 上一篇    下一篇

氮杂石墨烯碳纳米管复合材料负载Pt催化剂在甘油选择性氧化中的应用

张梦媛a, 孙妍妍a, 石娟娟a, 宁文生b, 侯昭胤a   

  1. a 浙江大学化学系生物质化工教育部重点实验室, 浙江杭州 310028;
    b 浙江工业大学绿色化学合成技术省部共建国家重点实验室培育基地, 浙江杭州 310012
  • 收稿日期:2016-10-19 修回日期:2016-12-08 出版日期:2017-03-18 发布日期:2017-03-22
  • 通讯作者: Zhaoyin Hou
  • 基金资助:

    国家自然科学基金(21473155,21273198,21073159);浙江省自然科学基金(L12B03001);浙江工业大学绿色化学合成技术国家重点实验室基金(GCTKF2014009).

Selective glycerol oxidation using platinum nanoparticles supported on multi-walled carbon nanotubes and nitrogen-doped graphene hybrid

Mengyuan Zhanga, Yanyan Suna, Juanjuan Shia, Wensheng Ningb, Zhaoyin Houa   

  1. a Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Department of Chemistry, Zhejiang University, Hangzhou 310028, Zhejiang, China;
    b State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology, Hangzhou 310032, Zhejiang, China
  • Received:2016-10-19 Revised:2016-12-08 Online:2017-03-18 Published:2017-03-22
  • Supported by:

    This work was financially supported by the National Natural Science Foundation of China (21473155, 21273198, 21073159), Natural Science Foundation of Zhejiang Province (L12B03001), and the foundation from State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology (GCTKF2014009).

摘要:

生物柴油因原材料来源广、可再生、安全性能好、环境友好及可替代石化柴油等优势被认为是一种极有发展前景的可再生能源,正逐步成为当今国际新能源开发的热点.作为生物柴油生产过程的主要副产物,甘油多相氧化制备具有高附加值的氧化产物是生物柴油产业链上的重要分支.目前,应用于该催化氧化体系的催化剂主要为负载型单金属(Au,Pd和Pt)和双金属(Au-Pd,Au-Pt和Pt-Bi)催化剂.其中,Au催化剂在碱性条件下对甘油氧化反应有较高的催化活性和甘油酸选择性,并且该催化剂稳定性高,不易在较高氧气压力的反应条件下因氧中毒而失活.但是,由于反应过程中碱的存在,反应体系中部分产物间可相互转化,从而掩盖催化剂的产物选择性本质,增大了产物分析、分离和催化剂作用机理研究的难度.而Pd和Pt催化剂不受酸、碱反应条件的限制,能够在无碱助剂作用下实现甘油催化氧化.与Au基和Pd基催化剂相比,Pt基催化剂可实现在酸性或中性反应条件下甘油选择性氧化产物的一步生成,同时具有较高的催化活性及稳定性,且氧化产物收率较高.
一直以来,以碳材料为载体负载的金属催化剂被广泛应用于甘油液相氧化反应.研究表明,催化剂活性与碳的孔径分布有关,随着碳载体微孔比例的增加,催化剂活性下降.此外,载体表面基团对金属活性有着重要影响.例如,载体表面含氧基团的吸电子作用可降低载体表面电子的流动性(电子密度和导电性),从而阻碍甘油氧化反应过程中OH-的吸附和再生,导致反应活性降低.因此,开发微孔比例小、富含负电性基团的碳载体成为甘油氧化过程中急需解决的问题之一.
本文通过热解碳纳米管(MWCNTs)和三聚氰胺的混合物,在碳纳米管表面直接生长得到氮杂石墨烯(NG-MWCNTs),并采用SEM,N2吸附,TEM和XRD对所得复合材料进行了表征.实验发现,相比于单纯的MWCNTs和直接热解三聚氰胺所得的产物CNx,NG-MWCNTs具有更高的比表面积(173 m2/g)和更大的平均孔径.此外,NG-MWCNTs非常适合作为Pt催化剂的载体,Pt平均粒径可小至1.4±0.4 nm.所制备的Pt/NG-MWCNTs催化剂在甘油选择性氧化反应中具有很高的催化活性和甘油酸选择性(甘油转化率和甘油酸选择性分别可达64.4%和81.0%),且具有可重复使用性能.Pt/NG-MWCNTs催化剂优异的催化活性不仅与载体表面高分散的Pt有关,而且与N原子对Pt的给电子作用有关.

关键词: 甘油, 氧化, 铂, 碳纳米管, 石墨烯

Abstract:

Selective oxidation of glycerol is a hot topic. Increased biodiesel production has led to glycerol oxidation over Au- and Pt-based catalysts being widely studied. However, Pt catalysts suffer from deactivation because of weak metal-support interactions. In this study, multi-walled carbon nanotube (MWCNTs)-pillared nitrogen-doped graphene (NG) was prepared by direct pyrolysis of melamine on MWCNTs, and the synthesized NG-MWCNT composite was used as the support for Pt. Characterization results showed that the surface area (173 m2/g) and pore volume of the NG-MWCNT composite were greater than those of bare MWCNTs and the separated melamine pyrolysis product (CNx). Pt (1.4 ± 0.4 nm) dispersion on the NG-MWCNTs was favorable and the Pt/NG-MWCNT catalyst was highly active and selective in the oxidation of glycerol to glyceric acid (GLYA) in base-free aqueous solution. For example, the conversion of glycerol reached 64.4% with a GLYA selectivity of 81.0%, whereas the conversions of glycerol over Pt/MWCNTs and Pt/CNx were 29.0% and 31.6%, respectively. The unique catalytic activity of the Pt/NG-MWCNTs is attributed to well-dispersed Pt clusters on the NG-MWCNTs and the electron-donating effect of the nitrogen dopant in the NG-MWCNTs.

Key words: Glycerol, Oxidation, Pt, Carbon nanotube, Graphene