Preparation and characterization of aluminosilicate supports with a synthesized layer of catalytic filamentous carbon: II. Synthesis of carbon nanofibers on a supported cobalt catalyst

The synthesis of a layer of catalytic filamentous carbon (CFC) on a Co catalyst supported by homogeneous precipitation onto the surface of aluminosilicate supports (ceramic foam and vermiculite) was studied. The effects of CFC layer synthesis conditions (the catalyst concentration on a support, the pyrolysis temperature of a propane-butane mixture, and the composition of the gas mixture) on the specific surface areas of supports, the yield of carbon (g C)/(g Co)), and the morphology of a surface CFC layer were examined. It was found that, in the case of ceramic foam, the concentration of cobalt hydroxide precipitated on the surface was lower by a factor of 15 and the yield of carbon was higher by a factor of 20–40 than those in vermiculite. The specific surface areas of supports, the yield of carbon, and the amount of synthesized carbon increased as the pyrolysis temperature of a propane-butane mixture was increased from 500 to 600°C. As found by scanning electron microscopy, the carbon content increased with pyrolysis temperature because of an increase in the length of carbon nanofibers. The properties (activity and stability) of biocatalysts prepared by the adsorption immobilization of a recombinant protein having glucose isomerase activity on CFC-Co-containing supports (ceramic foam and vermiculite) were studied.     

Preparation and characterization of supports with a synthesized layer of catalytic filamentous carbon: III. Synthesis of carbon nanofibers on nickel supported onto aluminum oxide

The synthesis of catalytic filamentous carbon (CFC) on catalysts prepared by supporting Ni²⁺ compounds onto the surface of various alumina modifications (macroporous α-Al₂O₃ and mesoporous ?-Al₂O₃ and δ-Al₂O₃) using two procedures (impregnation and homogeneous precipitation) was studied. The texture characteristics (specific surface area and pore structure) of the parent supports and adsorbents with a CFC layer were compared. The effect of the supporting procedure on the surface morphology of Ni/Al₂O₃ catalysts and the synthesized CFC layer was studied by scanning electron microscopy. It was found that the carbon yield on a macroporous catalyst prepared by homogeneous precipitation was higher than that on a catalyst prepared by impregnation by a factor of ～2. The CFC layer exhibited a mesoporous structure because of a chaotic interlacing of carbon nanofibers, and the synthesis of CFC on macroporous supports resulted in the formation of a bidisperse pore structure of the adsorbent. Active and stable heterogeneous biocatalysts were prepared by the adsorptive immobilization of enzymatically active substances (glucoamylase and nongrowing baker’s yeast cells) on CFC.     

Formation of a supported cobalt catalyst for the synthesis of carbon nanofibers on aluminum oxide

Comparative studies of the effect of the physicochemical characteristics of a support (aluminum oxide) on the formation of a supported Co catalyst and its activity in the pyrolysis of alkanes (propane-butane) were performed. The effect of the crystalline modification of alumina on the yield of catalytic filamentous carbon (CFC) ((g CFC)/(g Co)) was studied. The surface morphologies of Co-containing catalysts and synthesized carbon deposits were studied by scanning electron microscopy. It was found that carbon deposits with a well-defined nanofiber structure were synthesized by the pyrolysis of a propane-butane mixture in the presence of hydrogen at 600°C on supported Co catalysts prepared by homogeneous precipitation on macroporous corundum (α-Al₂O₃). The yield of CFC was no higher than 4 (g CFC)/(g Co). On the Co catalyst prepared by homogeneous precipitation on mesoporous Al₂O₃, the intense carbonization of the initial support; the formation of cobalt aluminates; and, as a consequence, the deactivation of Co⁰ as a catalyst of FC synthesis occurred. The dependence of the yield of CFC on the preheating temperature (from 200 to 800°C) of Co catalysts before pyrolysis was studied. It was found that, as the preheating temperature of supported Co/Al₂O₃ catalysts was increased, the amount of synthesized carbon, including CFC, decreased because of Co⁰ deactivation due to the interaction with the support and coke formation.     

Preparation and characterization of nanoporous carbon supports on a nickel/sibunit catalyst

A nanoporous composite carbon material was developed; this material was prepared by the synthesis of catalytic filamentous carbon (CFC) on a Ni catalyst supported onto the Sibunit carbon support. The texture characteristics (specific surface area and pore structure) of this material were studied. The effects of the conditions of supporting bivalent nickel compounds from aqueous or water-ethanol solutions in the presence of urea and the pretreatment of the parent Sibunit (oxidation and reduction) on the yield of synthesized carbon were considered. The distribution of Ni inside a Sibunit granule was studied using energy dispersive X-ray microanalysis. The surface morphology of the Ni/Sibunit catalyst, as well as the synthesized carbon layer, was studied by scanning electron microscopy. It was found that a maximum yield of carbon (50–60 g/(g Ni)) was obtained on the precipitation of nickel compounds from water-ethanol solutions with an ethanol concentration of 5 to 50 vol %. The preliminary surface oxidation or reduction of the parent Sibunit resulted in a considerable decrease in the yield of carbon (by a factor of 2 or more). The parent Sibunit phase occurred within the prepared nanoporous carbon material, whereas a shell formed by CFC occurred on the outside.     

Formation of a nickel catalyst on the surface of aluminosilicate supports for the synthesis of catalytic fibrous carbon

Conditions for the homogeneous precipitation of nickel hydroxide in the presence of urea onto the surface of aluminosilicate honeycomb monoliths, which were prepared based on clay, talc, and amorphous aluminum hydroxide, were examined. Factors affecting the concentration of supported nickel (synthesis time, starting solution concentrations, loaded amount of the support, and support calcination temperature) were studied. The possibility of supporting nickel hydroxide onto the surface of cellular ceramic foam, glass foam, and haydite was demonstrated. The morphology of nickel hydroxide particles, nickel metal particles on support surfaces, and carbon coatings synthesized in the course of the catalytic pyrolysis of a propane-butane mixture was studied by scanning electron microscopy.     

Synthesis of catalytic filamentous carbon on a nickel/graphite catalyst and a study of the resulting carbon-carbon composite materials in microbial fuel cells

The carbon-carbon composite materials obtained via the synthesis of catalytic filamentous carbon (CFC) on a Ni/graphite supported catalyst in the process of the pyrolysis of C₃–C₄ alkanes in the presence of hydrogen were systematically studied. The effects of the following conditions on the catalytic activity expressed as the yield of carbon (g CFC)/(g Ni) and on the character of CFC synthesis on graphite rods were studied: procedures for supporting Ni(II) compounds (impregnation and homogeneous precipitation), the concentrations of impregnating compouds (nickel nitrate, urea, and ethyl alcohol) in solution, graphite treatment (oxidation) conditions before supporting Ni(II) compounds, and the pyrolysis temperature of C₃–C₄ alkanes in the range of 400–600°C. Optimum conditions for preparing CFC/graphite composite materials, which are promising for use as electrodes in microbial fuel cells (MFCs), were chosen. The electrochemical characteristics of an MFC designed with the use of a CFC/graphite electrode (anode) and Gluconobacter oxydans glycerol-oxidizing bacteria were studied. The morphology of the surfaces of graphite, synthesized CFC, and also bacterial cells adhered to the anode was studied by scanning electron microscopy.     

New carbon-carbonaceous composites for catalysis and adsorption

Properties, structural features, and basic principles for the synthesis of some new carbon-carbonaceous composite materials (CCM) originating at the Boreskov Institute of Catalysis are discussed. The CCM are synthesized via chemical growth of carbon deposits in a pre-formed porous carbon matrix. Among the CCM are: Sibunit produced by supporting pyrocarbon (PC) on carbon black granules, carbon filaments (CFC) produced by decomposition of CH₄ over Ni or Ni–Cu catalysts, CFC on Sibunit, CFC on ultradispersed diamond, and systems such as CFC/CFC, PC/CFC, etc. Basic mechanisms of structure and texture formation of CCM and some of their properties as adsorbents and catalyst supports are reported.     

Corundum impregnation conditions for preparing supported Ni catalysts for the synthesis of a uniform layer of carbon nanofibers

Impregnation techniques for corundum (S _BET = 0.5 m²/g) as a support for Ni catalysts for C₃–C₄ alkane pyrolysis into catalytic filamentous carbon (CFC) are compared. The effects of the following factors on the uniformity of the active component (Ni) deposition on the inert support and on the CFC yield (g CFC)/(g Ni) are reported: (1) pH of the nickel nitrate solution, (2) presence of aluminum(III) nitrate in the solution, (3) addition of viscosifying agents (glycerol, glucose, sucrose) to the solution, (4) catalyst calcination conditions before pyrolysis, and (5) catalyst drying technique. The surface morphology of the Ni catalysts and of the carbon deposits resulting from the catalytic pyrolysis of C₃–C₄ alkanes in the presence of hydrogen has been investigated by scanning electron microscopy. The optimum way of preparing the supported Ni catalysts is by carrying out the incipient wetness impregnation of corundum with a nickel nitrate solution (0.05–0.1 mol/l) containing glycerol (20–25 vol %), drying the product in a microwave oven, and burning away the glycerol before alkane pyrolysis.     

Phosphorylated mesoporous carbon as a solid acid catalyst

Mesoporous carbon catalyst supports are attractive due to their wide chemical stability while potentially increasing mass-transport through and providing a path for larger molecules to access catalytic sites. Herein we report the synthesis of a phosphorylated mesoporous carbon solid-acid catalyst characterized by NH(3)-TPD and isopropanol dehydration.     

Synthesis of activated carbon foams with high specific surface area using polyurethane elastomer templates for effective removal of methylene blue

Carbon foams have gained significant attention due to their tuneable properties that enable a wide range of applications including catalysis, energy storage and wastewater treatment. Novel synthesis pathways enable novel applications via yielding complex, hierarchical material structure. In this work, activated carbon foams (ACFs) were produced from waste polyurethane elastomer templates using different synthesis pathways, including a novel one-step method. Uniquely, the produced foams exhibited complex structure and contained carbon microspheres. The ACFs were synthesized by impregnating the elastomers in an acidified sucrose solution followed by direct activation using CO₂ at 1000 ℃. Different pyrolysis and activation conditions were investigated. The ACFs were characterized by a high specific surface area (S_BET) of 2172 m²/g and an enhanced pore volume of 1.08 cm³/g. Computer tomography and morphological studies revealed an inhomogeneous porous structure and the presence of numerous carbon spheres of varying sizes embedded in the porous network of the three-dimensional carbon foam. X-ray diffraction (XRD) and Raman spectroscopy indicated that the obtained carbon foam was amorphous and of turbostratic structure. Moreover, the activation process enhanced the surface of the carbon foam, making it more hydrophilic via altering pore size distribution and introducing oxygen functional groups. In equilibrium, the adsorption of methylene blue on ACF followed the Langmuir isotherm model with a maximum adsorption capacity of 592 mg/g. Based on these results, the produced ACFs have potential applications as adsorbents, catalyst support and electrode material in energy storage systems.     

Synthesis of nitrogen-containing carbon materials for solid polymer fuel cell cathodes

The following nitrogen-containing supports with various nitrogen contents and structure and texture properties were synthesized: carbon nanofibers (N-CNFs) and amorphous microporous carbon materials (N-AMCMs). It was found that the above characteristics can be regulated by varying synthesis conditions: precursor compositions and reaction temperature and time. Mesoporous nitrogen-containing CNFs with a specific surface area of 30–350 m²/g and a pore volume of 0.10–0.83 cm³/g were formed by the catalytic decomposition of a mixture of ethylene with ammonia at 450–675°C. Microporous materials (N-AMCMs) with a specific surface area of 472–3436 m²/g and a micropore volume of 0.22–1.88 cm³/g were prepared by the carbonization of nitrogen-containing organic compounds at 700–900°C. An increase in the carbonization temperature and reaction time resulted in an increase in the specific surface area and microporosity of N-AMCMs, whereas lower temperatures of 450–550°C and reaction times of 1–3 h were optimal for the preparation of N-CNFs with a developed texture. It was found that milder synthesis conditions and higher nitrogen contents of precursors were required for obtaining high nitrogen concentrations in both N-CNFs and N-AMCMs. The synthetic method developed allowed us to prepare carbon supports with nitrogen contents to 8 wt %.     

Preparation and characterization of supports with a synthesized layer of catalytic filamentous carbon: IV. Synthesis of carbon nanofibers on a Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A comparative study of the synthesis of carbon layers, including catalytic filamentous carbon, on the surface of various alumina modifications was made. The synthesis was performed by the pyrolysis of alkanes (a propane-butane mixture) on Co/Al₂O₃ supported catalysts. The texture characteristics (specific surface area and pore structure) of the starting supports and adsorbents with a synthesized carbon layer were studied. The surface morphology of Co/Al₂O₃ catalysts and the synthesized carbon deposits was studied by scanning electron microscopy. It was found that carbon nanofibers were formed only on the catalysts prepared by the homogeneous precipitation of Co compounds onto the surface of macroporous α-Al₂O₃, whereas carbon deposits on mesoporous aluminum oxides did not exhibit a pronounced fibrous structure. The applicability of C/Co/Al₂O₃ carbon-containing adsorbents to the immobilization of the nitrile hydratase enzyme and the preparation of a biocatalyst for acrylonitrile hydration to acrylamide was considered.     

PEFC catalyst layers: Effect of support microstructure on both distributions of Pt and ionomer and cell performance and durability

In order to improve the performance and durability of polymer electrolyte fuel cells (PEFCs), various improvements in the microstructures of cathode catalyst layers (CLs) were initiated in the early 1990s. More recent advances in CL materials are highlighted, including carbon supports for improved accessibility of Pt nanoparticles (NPs), adsorption of ionomer on the Pt surface, high-oxygen-permeability ionomers, corrosion resistance of mesoporous and microporous carbons, and conductive ceramic supports with a fused-aggregate network structure. These approaches are summarized as stepwise improvements. The influences of the support structure on the distribution of Pt NPs and ionomer are reviewed, as well as their effects on performance and durability. These approaches for carbon supports are extended to conductive ceramic supports and the unique advantages are discussed.     

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.     

Carbon layer-coated ordered mesoporous silica supported Co-based catalysts for higher alcohol synthesis: The role of carbon source

Surface chemical properties of supports have an important influence on active sites and their catalytic behavio r.Here,we fabricated a series of cobalt-based catalysts supported by carbon layer-coated ordered mesoporous silica(OMS) composites for higher alcohol synthesis(HAS).The carbon layers were derived from different sources and uniformly coated on the porous surface of OMS.Combined with the characterization results of carbonized catalysts,it is demonstrated that the carbon layer-coated supports significantly enhanced the metal dispersion and increased the ratio of Co2+ to Co0 sites,which further increased the CO conversion and alcohols selectivity.Moreover,it is found that the catalytic activity changed in line with the amount of defects and surface oxygenic groups of carbon layers,which re sulted from the different carbon sources.The highest space time yield of C2+OH was 27.5 mmol gcat-1h-1)obtained by the catalyst coated with glucose-derived carbon layer.But the carbon source is not the key factor influencing the distribution of Co-Co2+ dual sites and shows little effect on selectivity in HAS.These results may guide for further design of carbon supported catalysts.     

多尺度炭材料担载铂作为稳定的电催化剂用于氧还原反应

炭载体的稳定性对于燃料电池电催化剂是至关重要的. 本文中采用酚醛树脂作为前驱体,二氧化硅为模板剂,制备了多介孔且石墨化程度高的炭载体（HGMC）. 相比于商品Vulcan XC-72,HGMC具有中等的比表面积和高的石墨化程度,因此在电位循环扫描过程中具有较高的化学稳定性,然而HGMC碳层堆叠的结构不利于传质. 为克服这一劣势,多壁碳纳米管（MWCNTs）作为隔离物加入至HGMC中以构建具有三维多尺度结构的载体（MSGC）. 与HGMC为载体担载Pt以及商品催化剂Pt/C-JM相比,由于炭载体的具有高稳定性以及三维多尺度结构,MSGC担载Pt后不仅使电催化剂的电化学稳定性提高,且氧还原反应过程中传质得到显著改善.     

Effect of processing temperature on growing bamboo-like carbon nanotubes by chemical vapor deposition

The present article demonstrates a simple, eco-friendly route for the fabrication of carbon nanotubes (CNTs) with different morphologies, including the fascinating bamboo-like structures without complex catalyst/support preparation procedures. A thermal chemical vapor deposition (CVD) technique that utilized natural pozzolan supports and a solid carbon source, that is, a mixture of camphor and ferrocene in a weight ratio of 20:1, was carried out at different temperatures where the ferrocene played also the role of catalyst. The pozzolan chemical composition and mineral identification were determined by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The morphology of the fabricated CNTs was studied via scanning and transmission electron microscopies (SEM and TEM). It was revealed that both conventional tubular and bamboo-like nanotubes grow at 750 °C while the bamboo-like morphology prevails at 850 °C. The better nanostructure uniformity at higher deposition temperature was accompanied by an improved nanotube graphitization degree that was verified by Raman spectroscopy. Yet, the reduction of the CNTs production yield was recorded by thermogravimetric analysis (TGA). The experimental data are interpreted and discussed as an interplay between the CNTs processing temperature, morphology and growth mechanism. Thus, the growth of either tubular or bamboo-like nanostructures is suggested to be ruled by the competitive surface and bulk diffusions of carbon onto and into the catalyst surface. The growth depends on the size of catalyst nanoparticles sintered at different temperatures. The favorable role of the pozzolan supporting materials in the formation of bamboo-like tubes is emphasized.     

一步法合成二甲醚整体式催化剂的制备及反应性能研究

以蜂窝陶瓷为载体、γ-Al₂O₃为惰性涂层、C301/HZSM-5为活性组分制备出一种整体式合成二甲醚催化剂。BET、XRD和SEM分析结果表明,活性组分均匀负载在载体表面上,催化剂具有良好的结构和织构特点。在固定床反应器中考察了整体式催化剂上CO加氢一步法合成二甲醚的反应性能,并与C301/HZSM-5颗粒（粉末）催化剂进行了比较。在温度260℃、压力4.0MPa、合成气空速1500mL/(g·h)的条件下,整体式催化剂上CO转化率达到79.62%,二甲醚选择性为70.58%,分别比C301/HZSM-5颗粒催化剂高出7.78%和9.44%。100h的稳定性实验结果表明,整体式催化剂可以保持较高的活性和选择性,而颗粒状催化剂的活性有明显的下降。
     

Synthesis and characterization of Pd catalysts supported on carbon microspheres for formic acid oxidation

A facile preparation of Pd catalyst using carbon microspheres as support was introduced in this paper. The carbon microspheres were prepared with a simple method from dextrose via hydrothermal process and used as catalysts support for formic acid electrooxidation. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses revealed that the as-prepared face-centered cubic crystal Pd nanoparticles were well-dispersed on the surface of the carbon microspheres, and the mean diameter of the nanoparticles was 8.8 nm. The effect of the support on the catalyst performance for formic acid electrooxidation was studied. The as-prepared catalyst showed the enhanced electrochemical surface active area and the higher electrocatalytic activity towards formic acid oxidation compared with Pd/CNTs and Pd/XC-72 catalysts prepared at room temperature. Electrochemical analysis suggested that the carbon microspheres might be good candidates to be used as the supports of catalyst for formic acid electrochemical oxidation.     

Monolithic catalyst supports with foam structure

The present article considers the production of monolithic catalyst supports with a foam structure. A model of an open cell foam material structure is described. Technological schemes for the production of ceramic and metal foam materials, alongside with the main properties of the latter and control algorithms are presented.