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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]

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]

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: 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: 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]