Synthesis and characterization of carbon-supported nanoparticles for catalytic applications

International audienc

Advanced Preparative Strategies for Activated Carbons Designed for the Adsorptive Storage of Hydrogen

Since air quality is a major public health concern, especially in urban areas, the use of alternative fuels for vehicular applications has been strongly encouraged. Of these fuels, hydrogen is the only one that can produce zero emission through fuel cells. However, the storage of such a very light and highly combustible gas has yet to be solved. Only adsorption storage is discussed in the present paper. It should be recalled that no material has been capable of meeting the recommended targets to date. Recent progresses in preparing suitable carbon structures for hydrogen storage are described, and new routes for characterising and correspondingly improving the micropore texture are explored

Influence of Water on the Dynamic Adsorption of Chlorinated VOCs on Active Carbon: Relative Humidity of the Gas Phase versus Pre-Adsorbed Water

The present work deals with the influence of water on the adsorption of two chlorinated volatile organic compounds (VOCs) on activated carbons (ACs) having very different pore textures and surface chemistry. Two kinds of moisture were considered, viz. pre-adsorbed on the AC or present as steam in the gaseous phase, at various relative humidities ranging from 30% to 75%. It is shown that the adsorption of the VOCs depends on the kind of moisture. If the latter is pre-adsorbed, water is just displaced by the VOCs (overshoot). The adsorption capacities of the AC remain unchanged and only some minor changes in the shape of the breakthrough front, corresponding to hindered diffusion, may sometimes occur. In contrast, the simultaneous adsorption of steam and VOC leads to competition between water and the chlorinated compound, with direct consequences on the adsorption kinetics and capacities of the AC. However, the decrease of the water-induced adsorption performances depends strongly on the AC and the VOC (through different VOC/AC and water/VOC interactions), and on the concentration of the VOC

PHONONS IN GRAPHITE INTERCALATED WITH BROMINE

We have investigated the phonon spectrum in stage 2 graphite intercalate with bromine by using inelastic neutron scattering. We have observed longitudinal and transverse phonons along the c direction as well as in the layer plane. Results are presented for energies up to 15 THz at 300 K. A linear chain model explains most of our results

EXFOLIATION DU GRAPHITE PAR TRAITEMENT LASER D'UN COMPOSÉ INTERCALAIRE

L'exfoliation de graphite a été réalisée par chauffage d'un composé intercalaire (graphite naturel - acide nitrique) au moyen d'un laser continu à CO2 et d'un laser YAG à impulsions. Les surfaces résultantes sont homogènes et nettement plus étendues que celles obtenues avec le même composé intercalaire par les procédés habituels de chauffage. Les expériences font ressortir l'intérêt du laser dans la recherche des conditions optimales d'exfoliation du graphite et dans les études visant à une meilleure compréhension du phénomène lui-même ; elles montrent clairement l'importance du choc thermique.For the first time graphite has been exfoliated by laser heating of an intercalated compound (natural graphite-nitric acid). A continuous CO2 laser and a pulsed YAG laser were used. Homogeneous surfaces were prepared which are larger than those obtained by a conventional heating process with the intercalated compound considered. Laser heating appears quite suitable for a better understanding of the exfoliation mechanism itself and for the finding of the best exfoliation conditions. The importance of the thermal shock is clearly evidenced

Band structure model and dynamical dielectric function in lowest stages of graphite acceptor compounds

A 2D band structure model is proposed to describe electronic states in the lowest stages (n = 1, 2) of GAC. The tight binding method is applied taking into account intra and interlayer nearest neighbour interactions. From the energies and wavefunctions of the π valence and conduction bands, the frequency dependence of the complex dielectric function is derived. This model enables us to quantitatively analyse recent results of reflectivity in the region of the plasma edge and at higher energy obtained for various GAC (Br2, ICl, SbCl 5, AsF5). From the theoretical fits we deduce the charge transfer coefficient for several classes of GAC.Un modèle bidimensionnel de structure de bandes est proposé pour décrire les niveaux électroniques dans les stades 1 et 2 des composés d'accepteur. En utilisant la méthode de la liaison forte, nous incluons les interactions intra et intercouches entre carbones voisins. A partir des énergies et fonctions d'onde des bandes π de valence et de conduction, la dépendance en fréquence de la fonction diélectrique complexe est établie. Ce modèle permet de rendre compte quantitativement des récents résultats de la réflectivité optique, dans la région de plasma et à énergie plus élevée, sur différents composés d'accepteurs (Br2, ICl, SbCl 5, AsF5). De l'analyse théorique des résultats nous déterminons le coefficient de transfert de charge pour plusieurs variétés de composé