Fibre de carbone

vignette|Petits morceaux de fibres de carbone (longueur 8 mm). La fibre de carbone se compose de fibres extrêmement fines, d'environ cinq à dix micromètres de diamètre, et est composée principalement d'atomes de carbone. Ceux-ci sont agglomérés dans des cristaux microscopiques qui sont alignés plus ou moins parallèlement à l'axe long de la fibre. L'alignement des cristaux rend la fibre extrêmement résistante pour sa taille. Plusieurs milliers de fibres de carbone sont enroulées ensemble pour former un fil, qui peut être employé tel quel ou tissé. Ce matériau est caractérisé par sa faible densité (1,7 à 1,9), sa résistance élevée à la traction et à la compression, sa flexibilité, sa bonne conductivité électrique et thermique, sa tenue en température et son inertie chimique (sauf à l'oxydation). Sa principale utilisation est de servir de renfort dans les matériaux composites, ce qui permet d'obtenir des pièces ayant de bonnes propriétés mécaniques tout en étant nettement plus légères

Structured Non-Noble Metal Catalysts for the Liquid-Phase Reduction of Nitroaromatics

Oliver Anthony Beswick

The industrial production of aromatic amines, essential intermediates for the synthesis of several drugs, dyes, pigments and agrochemicals, requires the use of heterogeneous catalysis. These molecules were formerly produced by the Béchamp reduction, a non-catalytic batch process requiring costly downstream separation steps. Catalytic approaches afford the implementation of continuous processes producing less waste. While it is generally not the primary goal when improving processes to make them more environmentally friendly, it is often one of the consequences, thereby improving the image of the chemical industry. The development of new catalysts is one of the major axes for optimizing industrial production of chemicals. Often multidisciplinary, it involves a better understanding of existing systems, advances in characterization and modelling techniques for the discovery of new catalytic materials. This thesis aims at designing new catalysts based on non-noble metals (e.g. Fe, Co, Ni) for the chemoselective hydrogenation of nitroaromatics in the liquid phase. The use of activated carbon fibres (ACFs) as a structured support has been at the centre of the strategy applied during this work in order to develop new catalysts capable of surpassing the best systems based on Fe, Co or Ni. The high porosity of ACFs, composed of very thin pores (~ 2 nm) and a high specific surface area, has been exploited to generate and stabilize highly dispersed crystallites of active phase. The formation of ~2 nm metal oxides (MOx) nanoparticles (NPs) resulting from the impregnation/pyrolysis of Fe, Co or Ni precursors within the ACFs was performed. The reduction of nitroaromatics with different functional groups was carried out by catalytic hydrogenation with molecular hydrogen and by catalytic transfer hydrogenation (CTH) with hydrazine as reducing agent. The MOx/ACF catalysts were shown to be active and selective under mild conditions in the CTH of para-chloronitrobenzene (p-CNB) to para-chloroaniline (p-CAN). The FeOx/ACF was tolerating many substituents of nitroarenes during the -NO2 hydrogenation. The CoOx/ACFHNO3 catalyst was less active compared to the Fe-based catalyst but afforded a meta-vinylaniline (m-VA) yield above 99% during the reduction of the meta-nitrostyrene (m-NS), exceeding, to the best of our knowledge, the best performance reported to date. The very low activity of the NiOx/ACF catalyst in CTH has prompted us to test Ni-based catalyst in the hydrogenation of nitroarenes with gaseous hydrogen. Raney Nickel is a well-known catalyst used in industry for this reaction. First, the existence of particles size effects was evaluated using unsupported Ni PVP-stabilized NPs (2¿14 nm). An antipathetic structure sensitivity of the meta-dinitrobenzene (m-DNB) hydrogenation to meta-nitroaniline (m-NAN) was demonstrated, showing a 4.6-fold increase in the turnover frequency over the 14 nm NPs. Once supported on ACFs and cleaned from PVP by a UV-ozone treatment, the 2 nm Ni NPs afforded an increase of selectivity towards m-NAN from 34 to 96% at close to full conversion (Xm-DNB = 99%). The selective transformation favouring m-NAN has been attributed to reactions taking place at the edges and vertices of the NPs. The Langmuir-Hinshelwood two-site kinetic model was consistent with the experimental data. The incorporation of gold to form Ni-Au (1:1) bimetallic NPs led to a significant increase in the selectivity (99%), possibly by mimicking the electronic

EPFL2017

Activated carbon fibers modified by metal oxide as effective structured adsorbents for acetaldehyde

Guillaume Bastien Baur, Lioubov Kiwi

Novel efficient adsorbents for acetaldehyde removal from diluted gas streams (similar to 1300 ppmv) have been developed. The adsorbents combine the properties of activated carbon fibers (ACF) and nanoparticles (NPs) of basic metal oxides (La2O3, CaO, MgO, ZnO, Al2O3). The adsorbents have been prepared by wetness impregnation of ACF using different precursors. The NPs are well dispersed and have average particle size below 2 nm. The ACFs-based adsorbents have an open regular macrostructure with low resistance to gas-flow (low pressure drop) and allow fast adsorption without any diffusion resistance. The NPs deposition provides up to 10-fold increase of acetaldehyde amount adsorbed as compared to non-modified ACF. The adsorption capacity increased with the basicity of metal oxides attaining 20 wt.% on La2O3/ACF. The materials are characterized by different techniques including temperature-programmed desorption (TPD) and high resolution scanning transmission electron microscopy (HRSTEM). (C) 2015 Elsevier B.V. All rights reserved.

Elsevier Science Bv2015

Structured Non-Noble Metal Catalysts for the Liquid-Phase Reduction of Nitroaromatics

Oliver Anthony Beswick

EPFL2017

Removal of VOC traces over activated carbon fibers

Structured Non-Noble Metal Catalysts for the Liquid-Phase Reduction of Nitroaromatics

Activated carbon fibers modified by metal oxide as effective structured adsorbents for acetaldehyde

Activated carbon fibers modified by metal oxide as effective structured adsorbents for acetaldehyde

Removal of VOC traces over activated carbon fibers

Structured Non-Noble Metal Catalysts for the Liquid-Phase Reduction of Nitroaromatics