【作者】 唐天地；

【导师】 李永丹；

【作者基本信息】 天津大学 ， 工业催化， 2005， 博士

【摘要】 催化裂解含碳气体生长的碳纳米纤维,其石墨结构受到生长催化剂的组成、制备方法以及生长条件的影响。本文以共沉淀法制备Ni-Cu/Al₂O₃、Co/Al₂O₃和以溶胶-凝胶-超临界干燥法制备Co/Al₂O₃（SG）催化剂,通过甲烷裂解制备了不同石墨结构的碳纳米纤维。在Ni-Cu/Al₂O₃和Co/Al₂O₃（SG）催化剂上生长的碳纳米纤维的碳层排布为鱼骨状,而在Co/Al₂O₃上生长的碳纳米纤维碳层排布呈平行状。对于以上生长的碳纳米纤维,利用高分辨电镜和红外光谱进行了研究。结果表明:碳纳米纤维的表面呈不十分规则的石墨结构,在Ni-Cu/Al₂O₃催化剂上生长的碳纳米纤维表面,局部区域呈暴露的石墨边缘,而其它两种催化剂上生长的碳纳米纤维表面则未观测到这种结构。三种碳纳米纤维表面均有大量的缺陷,在缺陷处不仅存在CH基团,而且由于甲烷和生长催化剂中存在氧,使得在碳纳米纤维的生长过程中形成微量含氧基团。用浓硫酸和浓硝酸的混合液,在有聚四氟衬里的高压釜中实现了对碳纳米纤维的可控氧化处理。采用TEM、XRD、N₂物理吸附、红外光谱和离子交换等手段研究了氧化处理对碳纳米纤维的织构性质和表面性质的影响。结果表明,在较高处理温度下造成碳纳米纤维均匀截断,使碳纳米纤维的织构性质发生了改变。对于在Ni-Cu/Al₂O₃催化剂上生长的碳纳米纤维,比表面、孔容和平均孔径均明显减小;而在另两种催化剂上生长的碳纳米纤维,比表面和孔容明显增加,但平均孔径没有发生变化。经过氧化处理的碳纳米纤维,表面引入了大量的含氧基团,如羧基、羧基酐、酚羟基、醌或酮类等。随着处理温度的提高,碳纳米纤维表面引入的含氧基团浓度也增大。不同石墨结构的碳纳米纤维表面对氧化剂的敏感性存在明显的差异,其中鱼骨类碳纳米纤维表面对氧化剂的敏感性明显高于平行类。新鲜的碳纳米纤维是疏水性的,经过氧化处理后变为亲水性,并且通过改变处理条件可以实现碳纳米纤维不同程度的亲水性。采用等体积浸渍法制备了碳纳米纤维负载的Pd、Pt和Pd-Pt双金属催化剂用于萘加氢活性和抗硫性研究。通过高分辨电镜、H₂脉冲化学吸附、TPR等表征手段对负载催化剂进行了表征。结果表明:碳纳米纤维表面引入的含氧基团的数量和性质强烈影响金属颗粒的分散度。随着处理温度的升高,引入的含氧基团浓度越高,金属颗粒在载体表面的分散就越好。碳纳米纤维负载的单金属Pd、Pt催化剂的萘加氢反应活性非常低,而负载的Pd-Pt双金属催化剂活性明显提高。碳纳米纤维负载Pd-Pt催化剂的活性随着载体处理温度的升高而提高。碳纳米纤维负载的Pd-Pt催化剂在萘加氢反应中显示较高的耐硫性,并且以平行类碳纳米更多还原

【Abstract】 The graphite structure of carbon nanofibers （CNFs） grown from catalyticdecomposition of carbonaceous gas depends on the catalyst, preparation method, anddepends also on the reaction conditions. In this thesis, the CNFs of different graphitestructures were prepared by methane decomposition on Ni-Cu/Al₂O₃ and Co/Al₂O₃catalysts prepared with coprecipitation, and a Co/Al₂O₃ （SG） catalyst prepared withsol-gel and a supercritical drying method. The CNFs grown on Ni-Cu/Al₂O₃ andCo/Al₂O₃ （SG） catalysts have a fishbone structure, while the CNFs grown onCo/Al₂O₃ catalyst have a parallel structure.The CNFs were investigated by a high resolution TEM and infrared spectroscopy（IR）. The result indicates that the surfaces of CNFs appears a degree of disorder ofgraphite structure. At the surface of CNFs grown on the Ni-Cu/Al₂O₃ catalyst, itappears graphite layered edges, but the same layered like edges cannot be seen on thesurfaces of the CNFs grown on the other two catalysts. It was recomfirmed by FTIRthat a large amount of defects on the surfaces of these three kinds of CNFs. Not onlyCH groups, but also some oxygen-containing groups are detected.A controllable oxidation treatment was realized using a mixture of concentratedsulfuric and nitric acid in an autoclave with teflon liner. TEM, XRD, N₂ physisorption,IR spectroscopy and ion exchange methods were adopted to investigate the influenceof oxidation treatment on the texture and surface properties of CNFs. The resultsindicate that a treating at high temperature induces a uniform cutting, which lead tothe change of texture properties of CNFs. As to the CNFs grown on Ni-Cu/Al₂O₃, thesurface area, pore volume and average pore diameter changed severely if treated at150 Co. For the CNFs grown on the other two cobalt catalysts, with the surface areaand pore volume increased obviously for sample treated at 180 Co, the average porediameter was almost not changed. Many kinds of oxygen-containing groups e. g.carboxyl, carboxylic anhydride, phenol, quinine or ketone etc. were induced on thesurface through oxidation treatment. The amount of oxygen containing groupsinduced increased with the treating temperature increased. The fresh CNFs arehydrophobic, whereas good wettability can be realized after oxidation treatment. Thecontrollable hydrophilicity is beneficial to the preparation of supported catalyst. It wasfound that the surface sensitivity of fishbone CNFs is higher than that of parallel type.The supported Pd, Pt and Pd-Pt catalysts were prepared by incipient wetnessimpregnation method and used for the naphthalene hydrogenation with the presenceof thiophene. The catalysts were characterized with high-resolution TEM, H₂chemisorption and temperature programed reduction etc. The results indicate that theamount and properties of oxygen-containing groups influence strongly the dispersionof metal particles. With the treating temperature increased, the concentration ofoxygen-containing groups increased, and the dispersion of metals on the surface ofCNFs was improved. The activity of supported Pd/CNFs and Pt /CNFs catalysts wasvery low, whereas the activity of Pd-Pt/CNFs catalysts were high. The activity of thePd-Pt/CNFs catalyst increased with the treating temperature increased. Furthermore,the supported Pd-Pt/CNFs catalyst showed an excellent sulfur resistance. The paralleltype of CNFs is better than that of fishbone type of CNFs for sulfur resistancecatalyst.更多还原