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（英文）

发布时间：2018-04-10 19:28

本文选题：甘油 + 氧化　；参考：《催化学报》2017年03期

【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,N_2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CN_x,NG-MWCNTs具有更高的比表面积(173 m~2/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.
[Abstract]:Biodiesel is considered to be a promising renewable energy source because of its advantages such as wide source of raw materials, renewable, good safety performance, environment-friendly and alternative to petrochemical diesel. It is gradually becoming a hot spot in the international new energy development.As the main by-product of biodiesel production, glycerol multiphase oxidation is an important branch of biodiesel industry chain.At present, the catalysts used in the catalytic oxidation system are supported monometallic Au-Pd and Pt) and bimetallic Au-PdNa-Au-Pt and Pt-Bi-based catalysts.The catalyst has higher catalytic activity and selectivity for glycerol oxidation under alkaline conditions, and the catalyst has high stability and is not easy to be deactivated by oxygen poisoning under higher oxygen pressure.However, due to the presence of alkali in the reaction process, some of the products in the reaction system can be converted to each other, thus masking the product selectivity nature of the catalyst, increasing the difficulty of product analysis, separation and study of the mechanism of catalyst action.However, PD and Pt catalysts are not restricted by the reaction conditions of acid and alkali, so the catalytic oxidation of glycerol can be realized without alkali promoter.Compared with au and PD based catalysts, Pt-based catalysts can achieve one-step oxidation of glycerol in acidic or neutral reaction conditions, and have higher catalytic activity and stability, and higher yield of oxidation products.Metal catalysts supported on carbon materials have been widely used in liquid-phase oxidation of glycerol.The results show that the activity of the catalyst is related to the pore size distribution of carbon, and the activity of the catalyst decreases with the increase of the micropore ratio of the carbon carrier.In addition, the surface group of the carrier has an important effect on the metal activity.For example, the electron absorption of oxygen-containing groups on the surface of the carrier can reduce the electron fluidity (electron density and electrical conductivity) on the surface of the carrier, thus hindering the adsorption and regeneration of OH ~ (2 +) in the oxidation of glycerol, resulting in the decrease of the reaction activity.Therefore, the development of carbon carriers with small proportion of micropores and rich negative groups has become one of the problems that need to be solved in the process of glycerol oxidation.In this paper, a mixture of pyrolytic carbon nanotubes (MWCNTs) and melamine was prepared by direct growth on the surface of carbon nanotubes (CNTs) to obtain azagraphene NG-MWCNTsO. The composites were characterized by SEMN2 adsorption TEM and XRD.The experimental results show that CNXM-MWCNTs have a higher specific surface area (173mt / g) and larger average pore size than those obtained from MWCNTs and direct pyrolysis of melamine.In addition, NG-MWCNTs are very suitable for the support of Pt catalyst. The average particle size of Pt can be as small as 1.4 卤0.4 nm.The prepared Pt/NG-MWCNTs catalyst has high catalytic activity and glyceric acid selectivity in the selective oxidation of glycerol (glycerol conversion and glyceric acid selectivity are 64.4% and 81.0%, respectively).The heterogeneous catalytic activity is not only related to the highly dispersed Pt on the surface of the support,It is also related to the electron donating effect of N atom on Pt.
【作者单位】：浙江大学化学系生物质化工教育部重点实验室;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;
【基金】：financially supported by the National Natural Science Foundation of China(21473155,21273198,21073159) Natural Science Foundation of Zhejiang Province(L12B03001) the foundation from State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology(GCTKF2014009)~~
【分类号】：O643.36

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