Easy synthesis of iron doped ordered mesoporous carbon with tunable pore sizes

Precise control of the pore sizes for porous carbon materials is of importance to study the confinement effect of metal particles because the pore size in nanosize range will decide the physical and chemical properties of the metal nanoparticles.In this paper,we report a new approach for the synthesis of iron doped ordered mesoporous carbon materials with adjustable pore size using Fe-SBA-15 as hard template and boric acid as the pore expanding reagent.The pore size can be precisely adjusted by a step of 0.4 nm in the range of 3-6 nm.The carbonization temperature can be lowered to 773 K due to the catalytic role of the doped iron.The present approach is suitable for facile synthesis of metal imbedded porous carbon materials with tunable pore sizes.     

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

Mn和Zr助剂对介孔碳负载钴基催化剂费托合成反应性能的影响

采用浸渍法制备了Mn和Zr改性的介孔碳负载钴基催化剂,采用X射线衍射（XRD）、比表面积测定、H₂程序升温还原（H₂-TPR）、H₂/CO程序升温脱附（TPD）及X射线光电子能谱（XPS）等手段对催化剂的物化性质进行了表征,采用固定床反应器对其F-T反应性能进行了研究。结果表明,Mn或Zr助剂的添加均降低了CH₄的选择性。其中,Mn助剂的添加提高了C_2-4的选择性,提高了烯烷比,而Zr的添加提高了钴物种的分散度,增加了反应活性位点,显著提高了钴基催化剂的F-T反应活性和C₅₊选择性。     

Fischer-Tropsch synthesis over cobalt catalysts supported on modified SiO2 with mesoporous silica

SiO₂ was modified by hexagonal mesoporous silica to form a mixture with meso-/macroporous sizes and used as support of Co catalysts for Fischer-Tropsch synthesis in a slurry phase. A synergistic effect on the activity of Co catalyst was found. The catalytic properties are related to the state of surface Co and the character of support.     

有序介孔碳CMK-3负载金纳米微粒复合材料的制备和表征

分别采用等体积浸渍-甲醛还原、等体积浸渍-氢气还原及溶胶负载法在介孔碳CMK-3上负载金纳米微粒;利用透射电镜和粉末X射线衍射仪对比分析了采用3种方法得到的复合材料的微结构和相组成;并测定了采用溶胶负载法得到的不同金含量的复合材料的热稳定性.结果表明,所制备的金纳米微粒的尺寸因制备方法不同而呈现明显差异;负载于复合材料中的金纳米微粒具有很好的热稳定性.     

Self-assembling and size-selective synthesis of Ni and NiO nanoparticles embedded in ordered mesoporous carbon and polymer frameworks

We demonstrate the self-assembling and size-selective synthesis of uniform and highly dispersed Ni or NiO nanoparticles with diameters below 12 nm embedded in ordered mesoporous carbon or polymer frameworks. Self-assembly is induced by evaporation of the solvent from a mixture of metal-containing liquid crystalline (LC) mesophases of triblock copolymer and transition metal nitrate hydrate, and the carbon source is low-polymerized phenolic resol. Characterization by XRD, N(2) sorption isotherms, TEM, HRSEM, ICP-AES, TG, and XPS techniques has indicated an ordered 2D hexagonal mesostructure, high surface areas between 524 and 721 m(2) g(-1), uniform pore sizes of about 4.0 nm, large pore volumes ranging from 0.34 to 0.58 cm(3) g(-1), and metal contents ranging from 0.6 to 10.0 wt%. There is a high degree of dispersion, and a small size of nanoparticles throughout the whole framework, without aggregation outside of the pores due to the confinement effect of the mesoporous ordered matrix. The mesoporous solids show excellent adsorption properties for dyes and permit an easy magnetic separation procedure. This method is expected to be applicable to other mesoporous transition metal(oxide)-containing carbon catalysts.     

有序中孔炭的制备及电性能研究

采用微湿含浸法制备了一系列具有不同比表面积和孔径分布的超级电容器有序中孔炭材料,同时采用Al-SBA-15为模板剂制得具有六方排列的空心炭管CMK-5.所制得的有序中孔炭的BET比表面积随糠醇加入量的增加而减小.电化学性能测试结果表明,在1mA·cm-2的充放电电流密度下各中孔炭材料比电容的大小顺序与其BET比表面积的大小顺序相一致.在所有样品中AlSC-0.8由于具有最大的比表面积,因此其比电容最大,达87.8F·g-1.倍率性能测试结果表明,具有CMK-3结构的SC-2.0的倍率性能最好,在50mA·cm-2的放电电流密度下其放电比电容接近AlSC-0.8有序中孔炭的水平.     

还原温度对双介孔钴基催化剂费-托合成性能的影响

通过等体积浸渍法制备了双介孔钴基催化剂,采用XRD、BET、SEM、H₂-TPR等手段考察了催化剂的性质,并研究了还原温度对催化剂结构及费托合成催化性能的影响。结果表明,随着还原温度的提高,催化剂活性位增加,活性增加,但增加到一定程度后活性降低,而甲烷选择性随着还原温度的提高逐渐增加,这是反应过程中催化剂表面存在的钴氧化物,使得水煤气反应变得活跃,烃产物移向低碳烃。     

含氮前驱体对氮杂有序介孔炭材料及其氧还原电催化性能的影响

燃料电池中贵金属铂的大量使用是阻碍其发展的关键因素,亟需探索高效廉价的替代型电催化剂.在目前的替代型非贵金属催化剂研究中,氮杂炭材料是一类氧还原反应催化活性最好、成本最低廉的催化剂,被认为是最有可能取代Pt催化剂而获得实际应用的催化剂.氮杂有序介孔炭材料因具有极高的比表面积和规整的孔道结构,可实现活性位点的密集组装与反应物料的快速传输,受到研究者的广泛关注.本文分别以苯胺、吡咯和邻菲罗啉为含氮前驱体,介孔分子筛SBA-15为硬模板,采用纳米浇铸法成功制备了具有高比表面积的氮杂有序介孔炭材料,系统研究了不同含氮前驱体对氮杂有序介孔炭材料的影响.采用氮气吸附-脱附等温线、透射电子显微镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)等方法研究了氮杂有序介孔炭的组成与结构,采用循环伏安法(CV)以及线性扫描伏安法(LSV)等手段考察了其电化学行为与氧还原反应极化性能.氮气吸附-脱附等温线结果表明,采用三种不同含氮前驱体制备的氮杂炭材料都对应Ⅳ型吸脱附等温线以及H4型滞后环,表明所制备的氮杂炭材料具有介孔结构.由TEM可以清楚地观察到氮杂炭材料已经成功地反转了SBA-15模板的孔道结构.同时发现,含氮前驱体对氮杂炭材料的比表面积和孔结构产生较大影响:以吡咯和邻菲罗啉为前驱体制备的炭材料C-PY-900和C-Phen-900的比表面积较高,分别为765和746 m2/g,而以苯胺为前驱体制备的炭材料C-PA-900比表面积较小(569 m2/g);三种炭材料平均孔径大小顺序为C-Phen-900 (3.7 nm)＜ C-PY-900 (5.0 nm)＜ C-PA-900 (5.9 nm),这是由于不同含氮前驱体在高温焙烧过程中热分解行为不同所致.XRD结果发现,含氮前驱体对氮杂炭材料的晶型基本没有影响,均为无定形碳.XPS结果表明,采用苯胺、吡咯以及林菲啰啉为前驱体制备的氮杂炭材料中氮含量基本相同,分别为3.13 at％,3.32 at％和3.33 at％,说明在相同热解条件下材料中的氮含量基本不受前驱体的影响,但不同配位环境的氮含量以及氮活化碳原子的含量却有较大差异,其氮活化碳原子的相对含量分别为15.60％,19.87％和23.04％.电化学测试结果表明,三种氮杂介孔炭材料的氧还原反应电催化活性顺序为C-PA-900＜C-PY-900＜C-Phen-900,其H2O2产率低于30％,说明氧还原反应经历4电子转移路径.在碱性条件下,所制氮杂有序介孔炭材料C-PY-900和C-Phen-900表现出较商品Pt/C催化剂更加优异的氧还原反应电催化性能.综上可见,通过改变含氮前驱体的类型可以有效调变氮杂炭材料的比表面积、孔道结构以及N 1s与C 1s化学态,从而调控氧还原反应活性,本文不仅制备出高活性的非贵金属氧还原电催化剂,同时也为高活性炭基电催化剂的可控制备提供了思路.     

氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢

氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPa H2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO2,Pt/TiO2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.     

阿拉伯糖基有序介孔碳修饰电极检测盐酸奈福泮的研究

以阿拉伯糖为碳源,介孔硅(SBA-15)为模板剂,用硬模板法制备有序介孔碳材料,采用场发射扫描电镜(Scanning Electron Microscopy,SEM)、透射电子显微镜(Transmission Electron Microscope,TEM)、全自动比表面及孔隙度分析仪(Brunner Emmet Te...     

介孔炭的孔结构对其负载的Ru基氨合成催化剂性能的影响

采用模板法合成了介孔炭(MC),研究了其孔结构对其负载的Ru基氨合成催化剂Ba-Ru-K/MC性能的影响,采用N₂吸附脱附、扫描电镜和透射电镜等手段对介孔炭的孔结构进行了表征.研究发现,介孔炭载体的孔结构取决于模板剂的用量,当SiO₂/C质量比为1.0时,所制介孔炭比表面积最大.介孔炭负载的Ba-Ru-K催化剂活性与其介孔比表面积相关.在425℃,10MPa和10000h^-1条件下,合成氨的反应速率为139mmol/(g_cat·h).     

Catalytic synthesis of carbon nanotubes over ordered mesoporous matrices

Pyrolytic decomposition of acetylene over the surface of nickel-, cobalt- and iron-containing ordered mesoporous MCM-41 silicas has been studied. Catalytically active matrices have been prepared by chemisorption of volatile metal acetylacetonate complexes on the silica surface. Reduction of the supported metal-containing compounds was carried out in hydrogen or acetylene atmosphere. Acetylene is used not only as a source of carbon in synthesis of the nanostructures but also as a reagent capable of reducing metal ions in the surface chemical compounds. Formation of carbon nanotubes and nanofibers is shown to depend on the pyrolysis conditions.     

Particle size effects in Fischer-Tropsch synthesis by Co catalyst supported on carbon nanotubes

The effect of Co particle size on the Fischer-Tropsch synthesis (FTS) activity of carbon nanotube (CNT)-supported Co catalysts was investigated. Microemulsion (using water-to-surfactant molar ratios of 2 to12) and impregnation techniques were used to prepare catalysts with different Co particle sizes. Kinetic studies were performed to understand the effect of Co particle size on catalytic activity. Size-dependent kinetic parameters were developed using a thermodynamic method, to evaluate the structural sensitivity of the CNT-supported Co catalysts. The size-independent FTS reaction rate constant and size-independent adsorption parameter increased with increasing reac-tion temperature. The Polani parameter also depended on catalyst particle size, because of changes in the catalyst surface coverage.     

Detecting pore size distribution of activated carbon by low-field nuclear magnetic resonance

In this study, the transverse relaxation time (T₂) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T₂ and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution.     

Synthesis, characterization, and electrochemical properties of ordered mesoporous carbons containing nickel oxide nanoparticles using sucrose and nickel acetate in a silica template

New ordered mesoporous carbons containing nickel oxide nanoparticles have been successfully synthesized by carbonization of sucrose in the presence of nickel acetate inside SBA-15 mesoporous silica template. The obtained samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, and transmission electron microscopy (TEM). The NiO nanoparticles were embedded inside the mesoporous carbon framework due to the simultaneous pyrolysis of nickel acetate during carbonization. The electrochemical testing of the as-made nanocomposites showed a large specific capacitance of 230 F g⁻¹ using 2 M KOH as the electrolyte at room temperature. This is attributed to the nanometer-sized NiO formed inside mesoporous carbons and the high surface area of the mesopores in which the NiO nanoparticles are formed. Furthermore, the synthetic process is proposed as a simple and general method for the preparation of new functionalized mesoporous carbon materials, for various applications in catalysis, sensor or advanced electrode material.     

In situ synthesis of ceria nanoparticles in the ordered mesoporous carbon as a novel electrochemical sensor for the determination of hydrazine

A novel ceria (CeO₂)–ordered mesoporous carbon (OMC) modified electrode for the sensitive amperometric determination of hydrazine was reported. CeO₂–OMC composites were synthesized via a hydrothermal method at a relatively low temperature (180 °C) and characterized by scanning electron microscopy (SEM), transmission electron microcopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The CeO₂–OMC modified glassy carbon electrode was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) and indicated good electrocatalytic effect to the oxidation of hydrazine. Under the optimized conditions, the present sensor could be used to measure hydrazine in wide linear range from 40 nM to 192 μM (R² = 0.999) with a low detection limit of 12 nM (S/N = 3). Additionally, the sensor has been successfully applied to detect hydrazine in real water samples and the recoveries were between 98.2% and 105.6%. Eventually, the sensor exhibited an excellent stability and reproducibility as a promising method for determination of hydrazine.     

Development of niobium-promoted cobalt catalysts on carbon nanotubes for Fischer-Tropsch synthesis

Cobalt-based catalysts were prepared by a wet impregnation method on carbon nanotubes (CNTs) support and promoted with niobium.Samples were characterized by nitrogen adsorption,TEM,XRD,TPR,TPO and H2-TPD.Addition of niobium increased the dispersion of cobalt but decreased the catalysts reducibility.Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K,1 atm and H2/CO=2 for 5 h.Addition of niobium enhanced the C5+ hydrocarbons selectivity by 39% and reduced methane selectivity by 59%.These effects were more pronounced for 0.04%Nb/Co/CNTs catalyst,compared with those observed for other niobium compositions.