The discovery of carbon nanostructures, essentially carbon nanotubes (CNT) and carbon nanofibres (CNF) has led to a big effort devoted to their synthesis, characterization, surface modification and use. Indeed, these structures have encountered application in a wide range of technological fields, such as adsorption, catalysis, hydrogen storage or electronics. Apart from the filamentous arrange of graphene sheets conducting to CNT or CNF, carbon can bond in other different ways to create structures with dissimilar properties. The pairing of pentagonal and heptagonal carbon rings can result in the formation of carbon nanospheres (CNS). This novel nanostructure has only now started to attract significant research activity. In its spherical arrangement, the graphite sheets are not closed shells but rather waving flakes that follow the curvature of the sphere, creating many open edges at the surface. Contrary to the chemically inert C 60 , the unclosed graphitic flakes provide reactive ''dangling bonds'' that are proposed to enhance surface reactions, establishing CNS as good candidates for catalytic and adsorption applications. Despite the embryonic stage of the field and the existing data being too scattered, this work is aimed to provide a comprehensive review of the existing literature related to CNS, exploring the different preparation routes employed, the critical characterization results as well as the applications studied so far.

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Hydrothermal reduction of CO 2 using Zn as reductant to obtain formic acid is a selective and efficient process. This process has the advantage of avoiding the use of gaseous hydrogen with all its safety and environmental concerns, and allowing an easier integration with CO 2 capturing steps such as CO 2 absorption in aqueous NaOH, because the latter solutions can be directly fed to the process as NaHCO 3. In this work, this reaction was studied in batch reactors at temperatures from 275 to 325ºC. Conversions up to 75% were obtained with selectivity towards formic acid near 100%, at residence times between 10 and 180 min. Reactions proceeds fast in the first steps of reaction, and it is slowed down when the oxidation of Zn is completed. The experimental results obtained were used to stablish a model that can explain both experimental data from this work and from literature with an averaged error of 13%. Using both the model and the experimental data the main variables of the process were analyzed: temperature, Zn/HCO 3 ratio, heating rate, Zn particle size, pressure reactor material and use of supercritical conditions. The optimum reaction conditions found were 300ºC with a rapid heating, and particle sizes of 0.75-1 mm. Zn excess dramatically improves the yield, but working with a lower excess can be compensated by working at pressures higher than 300 bar.

9Three different bimetallic Ru:Ni catalysts supported on a mesoporous silica MCM-48 10 were prepared by consecutive wet impregnations, with a total metal loading of ca. 3 % 11(w·w -1 ). Ru:Ni ratios spanned in the range of 0.15 -1.39 (w·w -1 ) and were compared with

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In this paper, the optimization of typical reaction variables for a pilot scale synthesis of carbon nanofibers (CNFs) using a fixed-bed reactor has been carried out to provide a more economically viable large scale production of these materials. Using a Ni/SiO 2 catalyst (10 wt % Ni) and ethylene as the carbon source, the optimum value of temperature, space velocity, and H 2 /C 2 H 4 ratio (v/v) in terms of carbon yield was 600 °C, 10000 h -1 , and 1:4, respectively. The modification of these variables caused a significant change in the type and amount of solid carbon recovered. Carbon product characterization demonstrated that CNFs with mesoporous character, large external surface, and good thermal stability and crystallinity were obtained. Finally, results demonstrated a successful scale-up by a factor of 45 in the pilot plant scale; a CNFs yield of 106 g CNFs /g catalytic metal could be obtained at optimal conditions during a reaction time of 60 min at optimal conditions in the pilot plant scale. For the same reaction conditions, only 80 g CNFs /g catalytic metal were obtained in the laboratory reactor.

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