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Abstract: Carbon nanofibers (CNFs) have been used as templates for manipulating the properties of Ni catalyst particles. Both incipient wetness impregnation and deposition–precipitation have been used to prepare the catalysts. Relatively well-dispersed Ni nanoparticles have been prepared on oxidised CNFs by incipient wetness impregnation. The diameter of the CNFs has been shown to have a significant effect in determining the Ni crystal size. In addition, CNFs are suitable templates to induce microstrain to metal particles. Such microstrain has significant effects on the activity of Ni crystals during ethane hydrogenolysis. This provides new opportunities to manipulate the crystal size and activity of the metal by selecting proper carbon nanofibers as support. TPO has been demonstrated as a powerful tool to study the CNF supported catalyst and to provide information on Ni loading and relative activity of NiO for CNF oxidation. [Copyright &y& Elsevier]

Abstract: Cu/CNF and Cu/CeO2/CNF catalysts have been synthesized and characterized on different nanostructured carbon nanofibers (CNF). The samples have been tested in isopropanol dehydrogenation. Cu/CNF show similar activity to Cu catalysts supported on activated carbon. Cu/CeO2 nanotubes have been synthesized on the CNF surfaces. The Cu/CeO2 nanotubes exhibit much higher activity and lower activation energy than Cu/CNF. The selectivity towards acetone depends on the fraction of CeO2 in the composites. High activity and selectivity has been achieved with a Cu12Ce5/CNF catalyst. [Copyright &y& Elsevier]

Aqueous phase reforming (APR) of ethylene glycol was performed at 225 °C and 30 bar in batch and continuous reaction conditions. The effect on the APR performance by functionalizing carbon supports with nitrogen and adding Mn to Pt-based catalysts was investigated. The presence of nitrogen species on the carbon surface and Mn-addition (PtMn) improved the catalytic activity and promoted H 2 production. XPS results suggest that the enhancement of the catalytic activity may be attributed to charge transfer from platinum to the nitrogen groups and Mn. Pt-based catalysts were stable under the studied reaction conditions, while up to 97 % of the manganese leached into the liquid solution during APR. However, the catalytic activity was maintained even with such significant decrease in Mn content, indicating that only a small amount of Mn is necessary to maintain the promotional effect on Pt during APR. [Display omitted] • Electronic interactions between Pt-N and Pt-Mn led to enhanced catalytic activity. • N-doped carbon nanofibers effectively improved H 2 yield in aqueous phase reforming. • Pt-based catalyst promoted with Mn presented higher H 2 yield and selectivity. • Metal-support interactions are key factors in promoting catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanofibers (CNFs) with different microstructures were synthesized as the support of Pt catalyst for decalin dehydrogenation to evolve pure hydrogen. The results show that in a liquid-film state at the temperature of 240°C for reactor external heating, 5wt% Pt catalyst supported on platelet CNFs gives a TOF of 732.4mol H2/mol metal in 2h. The microstructure of CNFs and the metal particle size have great impact on the performance of the catalyst for the reaction. [Copyright &y& Elsevier]

A single-step chemical vapor deposition method using simple gaseous precursors was employed to grow nitrogen-doped carbon nanofibers from Fe and Ni particles on the surface of expanded graphite (N-CNF/EG). Due to the high electronic conductivity of the expanded graphite the N-CNF/EG could be used as electrocatalysts without the need for harsh purification procedures. Electrochemical testing showed that the N-CNFs grown from Fe exhibited a notable activity for the oxygen reduction in both acidic and alkaline electrolyte, in addition to demonstrating a high durability with a well-preserved catalytic activity after 1600 cycles in O 2 -saturated 0.5 M H 2 SO 4 . Physicochemical characterization revealed the formation of N-CNFs with a bamboo-like structure, encapsulated Fe particles and high pyridinic nitrogen content. The combination of high ORR-activity, an easily scalable synthesis approach and a highly conductive support material makes N-CNF/EG a promising oxygen reduction catalyst for low temperature fuel cells. [ABSTRACT FROM AUTHOR]

Transition metals such as Fe and Ni are the most commonly used catalysts for the growth of carbon nanofibers (CNFs) via CCVD method, and they always remain in the raw products. Much attention has been paid to purify CNFs, i.e., to remove residual metal particles and supports, before their use in most cases. However, some recent studies show that the residual metal particles usually attach at the tips of CNFs, and exhibit a different shape in comparison with the initial metal catalysts and as a result unique catalytic performance. The present review focuses on the state-of-the-art of the developments of synthesis of reshaped Fe and Ni particles at the tips of CNFs and their catalytic applications in cellulose conversion, selective hydrogenation and ammonia decomposition. In particular, effects of catalyst support, carbon source and its concentration, reaction temperature and etching gas are discussed. Moreover, the carbon adsorbates induced effect is highlighted as one of the key factors governing the reshaping of Fe and Ni particles. [ABSTRACT FROM AUTHOR]

Ni nanoparticles at the tips of carbon nanofibers (Ni-CNFs) were synthesized by catalytic chemical vapor deposition (CCVD) method using CH 4 as the carbon source, and then employed as catalysts for the generation of H 2 from ammonia decomposition. The morphology of Ni catalysts is highly sensitive to the ratio of CH 4 to H 2 . Especially for the CH 4 /H 2 ratio of 4, the as-obtained Ni-CNFs catalyst shows higher H 2 formation rate, which could be due to more accessible facets to the reactants and unique shape effect. Meanwhile, this catalyst also shows good thermal stability, possibly owing to the highly dispersed and spatially isolated Ni nanoparticles by CNFs. Moreover, effect of the surface carbon coverage on the orientation of Ni crystal facets and the matching degree between graphene sheet and Ni crystal facet were investigated by DFT calculations. Finally, a possible formation mechanism of shaped Ni catalysts was discussed by combining experimental and theoretical results. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe-CNFs/CMFs catalysts were prepared by using CCVD method. [•] Fe particles located on the tops of carbon nanofibers. [•] Fe crystal phases were changed from Fe3C to α-Fe(C) when from 0.20 to 0.33atm. [•] Fe3C and α-Fe(C) crystal phases were easily nitrided into Fe2N. [•] Structured polyhedral Fe2N catalyst was more active for ammonia decomposition. [ABSTRACT FROM AUTHOR]

Highlights: [•] Monolithic structures, microchannel reactors and carbon nanofibers on carbon felt have been studied. [•] All reactors provide good FT activity, selectivity and stability. [•] All reactors have good mass and heat transfer properties. [•] The reactors can be operated without significant internal diffusion limitation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Efficient Co catalyst on 3-D structured carbon nanofiber (CNF)/carbon felt (CF) as compact F–T synthesis reactor. [•] Improved stability by coated thin layer on CNFs. [•] High thermal conductivity. [•] High activity and selectivity. [ABSTRACT FROM AUTHOR]

Abstract: A cobalt based Fischer–Tropsch synthesis (FTS) catalyst, supported on a carbon nanofibers/carbon felt composite (Co/CNF/CF) was studied in situ at realistic conditions. The catalyst was monitored by X-ray absorption spectroscopy (XAS), high-resolution X-ray powder diffraction (HR-XRPD) and Raman spectroscopy, while changes in the gas phase were observed by mass spectrometry (MS). Transmission electron microscopy (TEM) was also applied to characterise the catalyst. The catalyst has a bimodal particle size distribution and exhibits a high deactivation rate. During the in situ study the catalyst appears to reduce further at the induction period of FTS, while crystallite growth is been detected in the same period. At steady state FTS the amount of metallic Co is constant. A change in the volumetric flow towards higher conversions did not affect the degree of reduction or the crystallite size of the catalyst. Post-treatment at 400°C under H2 atmosphere leads to sintering of the cobalt particles, while a CO treatment followed by H2 treatment creates a catalyst rich in hexagonal close packed cobalt through the formation of a Co2C intermediate. [Copyright &y& Elsevier]

Abstract: Proposing a plausible model for fishbone-type carbon nanofiber (f-CNF) proves to be a challenge. A practical approach to the construction of a cone-helix model is suggested on the basis of early experimental observations and from a geometric perspective. With the introduction of disclination angle and overlap angle into graphene sheets, the resultant helical cones have variable morphologies which rationalize the broad distribution of the f-CNF apex angles. A fraction of overlap angles can produce energetically favorable cone-helix models with high densities of coincident lattice points. Once the nearest coincident points to the apex is identified, both the overlap angle and the degree of graphitic alignment can be obtained. Periodic boundary conditions are imposed on the cone-helix models to depict the f-CNF morphologies along the principal axes. The lattice strain induced by the multi-layered model is found to have a negative effect on the structural stability. After the central parts of f-CNFs are removed, the lattice strain around the cone tips is eliminated, and the cone-helix model of more graphite layers is energetically more favorable. X-ray diffraction simulations are finally conducted to evaluate the reliability of the proposed models and to reveal the identity of the reflections at the diffraction angle of 44.5°. [Copyright &y& Elsevier]

Abstract: A novel approach to synthesize platelet carbon nanofibers (PCNFs) is proposed by taking advantage of the flat interfaces between Fe nanoparticles and flake supports. PCNFs are produced when Fe nanoparticles are supported on flakes of mica, SiO2 and graphite, and only fishbone carbon nanofibers (FCNFs) are obtained when γ-Al2O3 is used as a support. The crystalline perfection of PCNFs is found to depend on the dispersion of the catalyst and the surface roughness of the support. Perfect PCNFs are obtained when mica, which has a high surface tension and a very flat surface, is used as a support. The yield of PCNFs changes little with the nature of the support but is strongly related to the size of Fe nanoparticles and the preparation method of the Fe catalysts. [Copyright &y& Elsevier]

Abstract: Fe nanoparticles on the top of carbon nanofibers (CNFs) were synthesized by catalytic CVD on a purpose as catalysts for ammonia decomposition. The size and shape of Fe particles on the top of CNFs depended on the Fe particle reconstruction and CNF morphology. On a mica support Fe catalyst, platelet structure of CNFs was obtained with small, uniform, and unwrapped Fe particles on the top. HRTEM illustrated that the Fe particle surface is covered by a few graphene layers, which redissolves into the Fe particle and does not prevent the access of NH3 to active surface sites at reaction conditions. The catalyst is highly active and stable because the Fe particles are highly dispersed and physically isolated by CNFs, and the surfaces are largely exposed to the reactants. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanofibers (CNFs) were synthesized by CO disproportionation on iron catalyst at CO concentration between 58.3% and 75.0%, H2 concentration between 8.3% and 25.0% and reaction temperature between 833 and 913K. The time-depending rate of CNFs growth as a function of time was determined by an on-line mass spectrometer and the morphologies of all CNFs products were observed by electronic microscopy. Not only the CNFs growth rate but also the morphology of the grown CNFs were shown to vary with the three operating variables. SEM and TEM images showed that the three-dimensional morphologies of the CNFs were twist, helical or straight and an interesting relationship between the maximal growth rate and the morphology was observed. When the growth rate was between 0.8 and 0.9mmol/(sgcat), the CNFs were twist. As the growth rate increased to 1.0mmol/(sgcat), more helical nanofibers appeared. Straight nanofibers were produced when the growth rate reached the level of 1.2mmol/(sgcat). Finally when the rate of CNFs growth was high at 1.8mmol/(sgcat), the absolute majority of the solid products was amorphous carbon coexisting with some short and thick nanofibers. Under different operating conditions, the crystal faces of the catalysts had different anisotropy properties for carbon deposition, thus producing CNFs with different morphologies. [Copyright &y& Elsevier]

Abstract: Carbon nanofibers (CNFs) are grown on metal catalysts and electrochemical treatment is used to remove the metal catalyst residuals from the as-grown CNFs. For comparison, the CNFs are also purified by a chemical method and a thermal method. The oxygen reduction reaction (ORR) properties of CNFs purified by these three methods are examined by cyclic voltammetry. CNFs treated by the electrochemical method have a more positive ORR onset reduction potential and peak potential compared with those treated by chemical and thermal methods, and this is because the microstructures of CNFs are less changed by electrochemical method. However, they have a lower electrochemical capacity and ORR peak current than those treated by the chemical method. Cyclic voltammetric measurements at different scan rates confirm that the oxygen reductions on CNFs treated by electrochemical and chemical methods are controlled by diffusion, while on CNFs treated by thermal method is partially influenced by diffusion. [Copyright &y& Elsevier]

Abstract: The rational design of the carbon nanofiber catalysts for oxidative dehydrogenation of ethylbenzene (ODE) has been discussed based on a reviewed reaction mechanism. The synthesized carbon nanofibers with systematically varied graphitic platelet orientations have been used as a model system for the rational catalyst design, in respect to the carbon nanofiber properties such as the amount of basic groups, the crystallinity, and the ratio between the prismatic area and the basal plane area. Well defined carbon nanofibers have been synthesized by hydrocarbon or carbon monoxide decomposition on the sub-iron group catalysts and at selected preparation conditions. The catalytic test in a fixed bed reactor at a temperature of 400°C shows that the stable activity and selectivity can be obtained on the well-defined carbon nanofibers catalysts. Removing the residual metal in carbon nanofibers does not evidently influence the catalytic behavior whereas the lower conversion of ethylbenzene can be observed on the high-temperature treated carbon nanofiber samples. No clear evidences are found for the catalytic behavior being related to the surface area and graphitization degree of carbon nanofibers. The basic oxygen-containing groups are identified as the active sites by TPD–MS and a special method suggested by Boehm. The ratio between the prismatic surface area and the basal area has been identified as the most important parameter for the rational catalyst design. The fish-bone catalysts CNF 20 seems to be the best catalyst in the samples studied in the present work, due to the large number of basic edge groups, the optimum ratio between the prismatic and basal plane area. It can result in a delicate balance in the redox catalytic cycle. As a consequence, the formation of CO2 can be reduced. [Copyright &y& Elsevier]

Abstract: Nanocomposite catalysts containing carbon nanofiber (CNF) and Cu-Ce-Zr mixed metal oxide (MMO) have been prepared by homogeneous co-precipitation with urea. The water-gas shift (WGS) reaction has been used as test reaction. The CNF-containing nanocomposite catalysts exhibit similar overall catalytic activity and stability as the corresponding CNF-free catalyst. Thirteen weight percent of the MMO could be replaced by CNF without decreasing the overall activity and stability of the catalyst. The specific activity of the nanocomposites based on the total metal oxide content is similar or higher than the activity of the CNF-free material, depending on the CNF content. Similar activation energies are, however, obtained for the CNF-free and CNF-containing materials. We cannot exclude that the CNF material acts as reaction promoter under certain conditions, but suggest that the impact of CNF addition on the precipitation of the mixed oxide particles, and hence the catalytic activity relative to the CNF-free MMO, should also be considered. CNF may be regarded as inert dispersing agent material improving the precipitation of the MMO under conditions where the co-precipitation of the MMO precursors does not result in materials with high surface area. [Copyright &y& Elsevier]

Abstract: Catalytically grown carbon nanofibers, a novel mesoporous carbon material for catalysis, were synthesized by the decomposition of carbon-containing gases (CH4, C2H4 or CO) over supported nickel-iron alloy and unsupported iron. It was shown that the structures of as-synthesized and modified CNFs, including the arrangement of the graphenes in CNF, and the crystallinity and texture of CNF depended on the catalyst composition and the type of carbon-containing gas. Three types of CNFs with different microstructures were obtained: platelet CNF (Fe–CO), fishbone CNF (supported Ni–Fe alloy-CH4, C2H4 or CO) and tubular CNF (supported Ni–CO). All the CNFs were mesoporous carbon materials possessing relatively high surface areas (86.6–204.7m2/g) and were highly graphitic. Purification with acid-base treatments or high temperature treatment removed the catalyst residue without changing the basic structures of the CNFs. However, annealing significantly decreased their surface areas through the formation of loop-shaped ends on the CNF surfaces. Oxidative modification in the gas and liquid phases changed the structures only slightly, except for oxidation in air at 700°C. The structures and textures were studied using SEM, TEM, XRD, BET and TGA. [Copyright &y& Elsevier]

Abstract: Carbon nanofiber/graphite-felt composite with desirable shape and size has been synthesized by the method of catalytic chemical vapor deposition (CCVD) through the growth of carbon nanofibers (CNFs) on the surface of the graphite microfibers of the felt. Scanning electron microscopy (SEM), N2-physisorption, and a mechanical strength test have been used to characterize the morphology, the texture properties, and the mechanical strength of the CNF/graphite-felt composites, aiming at a detailed understanding of the relationship between structure and property. The physico-chemical properties, especially the mechanical strength of the composites, have been investigated as a function of the ratio (w/w) between the CNFs and the graphite felt. Both the compressive strength and the apparent density of the composites were found to vary with the CNF yield (w/w). Their maximum values are reached at a CNF yield of about 6. Very few fragments are desquamated from the composite with a CNF yield below 5 under vigorous agitation, indicating stable anchorage of CNFs on the graphite microfibers. A distinct mesoporous character, a large external surface area and high mechanical strength make CNF/graphite-felt composites attractive as a catalyst for the oxidative dehydrogenation of ethylbenzene to styrene (ODE). An optimized ratio of 4.5 between the CNF and graphite felt in the composites exists for the catalyst in the ODE reaction with respect to both the styrene yield and mechanical strength. Moreover, the composite exhibits much greater catalytic stability than activated carbon. [Copyright &y& Elsevier]