碳纳米纤维的酸处理及其负载Pd-Pt的催化萘加氢活性

采用浓硝酸和浓硫酸混和液(90、120、150 ℃)处理鱼骨类和平行类碳层排布的碳纳米纤维. 运用高分辨电镜、红外光谱和离子交换对碳纳米纤维的表面性质进行了表征，并考察了以两种碳纳米纤维为载体的Pd-Pt催化萘加氢活性. 结果表明，碳纳米纤维的碳层排布不同使混酸处理的鱼骨类表面生成的极性含氧基团的量明显高于平行类表面，以前者为载体得到Pd-Pt催化剂金属颗粒的分散程度明显高于后者，其负载的Pd-Pt催化萘加氢活性也较高.     

碳纳米纤维在浓硝酸-浓硫酸溶液中表面氧化对其负载的Pd-Pt催化剂颗粒分散状态的影响

摘要用混合的浓硝酸和浓硫酸在不同温度下氧化处理催化生长的碳纳米纤维. 利用X射线衍射、 N2物理吸附、 FTIR和离子交换研究了氧化处理对碳纳米纤维织构性质和表面含氧基团生成的影响. 采用等体积浸渍法制备碳纳米纤维负载Pd-Pt催化剂, 并利用高分辨电镜和脉冲H₂化学吸附对Pd-Pt金属颗粒的分散状况进行了研究. 结果表明, 经过氧化处理的碳纳米纤维表面生成了含氧基团, 生成量随着处理温度的升高而升高, 负载的Pd-Pt催化剂的分散程度也随着表面含氧基团浓度的增大而提高, 同时对后者的作用机理进行了讨论.     

柴油深度脱芳烃Pd-Pt/USY催化剂的EXAFS研究

为满足日趋严格的环保要求和适应汽车工业的快速发展,柴油深度脱芳烃已成为国内外普遍关注的课题．近年来的研究表明,Pd－Pt/USY催化剂具有较高的芳烃加氢活性和较强的耐硫中毒能力[’－     

高酸度和高水热稳定性MCM-41的合成及萘加氢催化性能

以十六烷基三甲基溴化铵为模板剂,以具有Y沸石次级结构单元的水凝胶为前驱体,在pH=10左右的条件下合成了与MCM-41相类似的介孔分子筛。同时利用各种表征手段对合成的样品进行了一系列的表征。结果表明，所合成的样品具有六方规整结构和较厚的孔壁，并具有较强酸强度和水热稳定性。同时，考察了其负载Pd-Pt活性组分后的萘加氢反应活性和抗硫性,并与常规法合成的具有相同硅铝比的MCM-41载体进行了比较。     

纳米碳纤维负载钯催化剂在Heck反应中的应用——载体相互作用的影响

使用多元醇还原法制备了均匀分散的钯纳米颗粒.将钯纳米颗粒负载于板式、鱼骨式和管式纳米碳纤维,得到稳定、可重复使用的非均相催化剂.实验结果表明,钯纳米胶粒同载体之间的电位差对钯在载体上的负载量、粒子大小以及Heck反应中钯的溶失量有很大的影响.在制备过程中,增加钯纳米胶粒同纳米碳纤维表面的电位差能够大大降低钯在Heck反应中的流失.催化剂的反应活性随钯粒子的增大而降低.     

Zr的添加对稀燃天然气汽车尾气净化催化剂Pd-Pt/Al2O3性能的影响

Pd-Pt双金属基甲烷氧化催化剂的催化活性、抗水热老化性和耐硫性在一个通有模拟稀燃天然气汽车尾气成分的固定床反应器中进行检测.研究发现Zr掺杂的Pd-Pt/Al₂O₃ (Pd-Pt/Zr_xAl_(1-x)O_(3+x)/2)提高了催化的催化活性、抗水热老化性和耐硫性.以共沉淀法制备Zr : Al的摩尔比分别为0 : 1、0.25 : 0.75、0.5 : 0.5、0.75 :0.25和1 : 0的材料为载体材料.双金属催化剂的活性组分分别为1.5% (w,质量分数)的Pd和0.3% (w)的Pt,活性组分Pd、Pt通过共浸渍的方法浸渍到以上载体材料上制备得到一系列整体式催化剂.分别采用低温N₂吸脱附、X射线衍射(XRD)、H₂程序升温还原(H₂-TPR)、O₂程序升温氧化(O₂-TPD)及X射线光电子能谱对制备的催化剂进行表征.结果显示Zr的加入使催化剂的载体材料结晶度提高,活性组分的分散度也得到了相应的提高.同时二价Pd物种与周围电子密度分别增加.相比于Pd-Pt/Al₂O₃和Pd-Pt/ZrO₂催化剂,在不同条件预处理后, Zr的添加对催化剂的性能有明显的提高,其中催化剂Pd-Pt/Zr_0.5Al_0.5O_1.75展现了最好的催化活性、抗水热老化性以及耐硫性.     

Influence of surface functionalization via chemical oxidation on the properties of carbon nanotubes

The surface of carbon nanotubes (CNTs) was functionalized in different chemical oxidants, hydrogen peroxide, mixed concentrated HNO(3)/H(2)SO(4) and acidic KMnO(4) solution. The influences on the properties of CNTs were systematically investigated, such as the structure, the kinds and the contents of the formed surface oxygen-containing functional groups, the pH(PZC) values and the surface hydrophilicity using XRD, HREM, FTIR and chemical titration. The results show that the kinds and the contents of the surface oxygen-containing groups are dependent on the functionalization methods. The formation of the oxygen-containing groups can decrease pH(PZC) values and improve surface hydrophilicity of CNTs. The dispersion of the supported Pd-Pt particles on the functionalized CNTs and their catalytic activity in the profile reaction of naphthalene hydrogenation to tetralin are both promoted due to the presence of these oxygen-containing groups.     

Ce改性碳纳米管负载过渡金属磷化物用于电化学水分解

氢能是未来替代化石燃料的理想选择,可以通过电解水的半反应之一析氢反应制得,但其缓慢的反应动力学将会耗费大量的电池电压。因此,通过开发催化剂来降低电解槽的电压是解决这一问题的关键途径。本文经过简便的静电纺丝及碳化工艺得到Ce改性的碳纤维作为载体(Ce-CNFs),接着通过水热法及高温磷化法负载活性组分得到Co_x-Mo_y-P@Ce-CNFs,分别对催化材料的析氢反应(HER)和析氧反应(OER)电催化活性进行了研究。结果表明,在1mol/L KOH电解液中,仅需要160mV和323mV的过电位就能达到10mA/cm²的电流密度。将Co_x-Mo_y-P@Ce-CNFs作为阴极和阳极材料组装为整体水电解槽,在电流密度为10mA/cm²时,电解槽的电池电压为1.65V,在电化学耐久性测试中能够稳定保持8h。     

Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50 nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50 m²/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4 nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the C=C bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.