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2006 year, number 6


Pages: 547

Synthesis of Self-Supported Multi-Walled Carbon Nanotubes

J. Amadou, D. Begin, P. Nguyen, J.-P. Tessonnier, I. Janowska, T. Dintzer, E. Vanhaecke, M.-J. Ledoux and C. Pham-Huu
Laboratoire des Matriaux, Surfaces et Procds pour la Catalyse (LMSPC),
ECPM-Universit Louis Pasteur, 25, rue Becquerel, 67087 Strasbourg Cedex 02 (France)
Pages: 549-552

Abstract >>
Carbon nanotubes are generally synthesized in a fine powder with a very high specific volume and a low apparent density, which render their manipulation extremely difficult and hazardous. Here we demonstrate a simple and reliable method for the direct synthesis of multi-walled carbon nanotubes (MWCNTs) supporting each other in a controlled macroscopic shape and size by applying an external constraint on the reactor during the synthesis. The MWCNTs are highly entangled allowing a natural compacting of the macroscopic pieces without fine formation, making subsequent handling easier. The present synthesis method addresses many critical problems encountered with the use of carbon nanotubes as a macroscopic building-block materials.

Preparation of Pd/AC Catalyst by Ion Exchange

A. Cabiac1, G. Delahay1, R. Durand1, P. Trens1, B. Coq1 and D. Ple2
1Laboratoire de Matriaux Catalytiques et Catalyse en Chimie Organique, UMR 5618-CNRS-ENSCM, Institut Charles Gerhardt FR 1878, 8, rue de l'Ecole Normale, Montpellier CEDEX 5 (France)
2Groupement de Recherches de Lacq - ARKEMA, rte de Bayonne, 64170 LACQ (France)
Pages: 553-558

Abstract >>
By choosing appropriate liquid oxidizing treatment, the carbonaceous surface of an activated carbon (AC) can be functionalised with carboxylic groups in a broad range of content. These carboxylic groups are necessary functions, in order to disperse, perfectly, palladium cations through exchange reactions: H+/Pd2+ or H+/Pd(OH)+. Reduction in liquid phase of a 4 mass %Pd/AC whose carbonaceous surface was previously oxidized by NaOCl leads to palladium particles with a particle size of 1.5 nm which are much smaller than Pd particles obtained from a 4 mass % Pd/AC whose carbon surface was not oxidized. The well dispersed catalyst was tested in hydrogenation of cinnamaldehyde and exhibits quite a high hydrogenation efficiency as compared to activities reported in the literature.

DeNOx Cu/Carbon Xerogels

A. Cabiac1, N. Job2, J.-P. Pirard2 and G. Delahay1
1Laboratoire de Matriaux Catalytiques et Catalyse en Chimie Organique, UMR 5618-CNRS-ENSCM, Institut Charles Gerhardt FR 1878, 8, rue de l'Ecole Normale, Montpellier CEDEX 5 (France)
2Laboratoire de Gnie Chimique, Institut de Chimie, Universit de Lige (Bt B6a), B-4000 Lige (Belgium)
Pages: 559-564

Abstract >>
Carbon materials with different pore texture have been prepared by evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels. These carbon xerogels have been characterised and used as copper catalyst supports in the Selective Catalytic Reduction of NO by NH3 at low temperature. Without metal, some activity is observed due to reaction between NO and NH3, but the NO conversion is strongly enhanced after copper introduction. High deNOx efficiency was obtained on these Cu/carbon xerogels at very low temperature and some pore texture effect was observed. However, special cares have to be taken to avoid carbon consumption and preserve its surface by keeping reaction temperature below 215oC.

On the Pore Size Distributions of Carbonaceous Catalysts and Adsorbents

D. K. Efremov1 and V. A. Drozdov2
1Boreskov Institute of atalysis, Siberian Branch of the Russian Academy of Sciences,
Pr. Akademika Lavrentyeva 5, Novosibirsk 630090 (Russia)
2Institute of Hydrocarbons Processing, Siberian Branch of the Russian Academy of Sciences,
Ul. Neftezavodskaya 54, Omsk 644040 (Russia)
Pages: 565-569

Abstract >>
The modeling of a low temperature nitrogen adsorption in graphite mesopores with rectangular sections having the aspect ratio of the side lengths more than 7:1 has been executed by using the grand canonical Monte Carlo (GCMC) method. The adsorption branches of obtained GCMC isotherms were processed with the purpose of calculation of the formal pore size distributions (PSDs) by the nonlocal density functional theory (NLDFT) and Derjaguin-Broekhoff-de Boer (D-BdB) method. It is shown that NLDFT underestimates the sizes of the model rectangular mesopores though gives good estimations of specific surface area and volume of the pores. Also, it is shown that D-BdB method very strongly underestimates specific surface area and overestimates total volume of pores. PSDs obtained from D-BdB method have a very wide distributive interval of apparent sizes and brightly expressed bimodal forms. Such completely wrong information about the size of the investigated model pores is a consequence of the macroscopic assumption of the D-BdB theory about the constancy of the capillary condensate density in pores at various pressures.

Avoiding Mass Transfer Limitations in Carbon Supported Catalysis by Using Carbon Xerogel as Supports

N. Job1, B. Heinrichs1, A. Lonard1, J.-F. Colomer2, J. Marien1 and J.-P. Pirard1
Pages: 571-575

Abstract >>
Porous carbon materials with tailored pore texture can be prepared by evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels. The pore size is easily controlled by the pH of the precursor solution. These materials, called "carbon xerogels", can be used as catalyst supports, like activated carbons. Since the texture of these materials is adjustable, it is possible to avoid diffusional limitations that are often encountered when a microporous activated carbon is used as support by choosing a support with the appropriate pore size. The meso- or macropore size of carbon xerogels can be enlarged so as to simplify the reactant diffusion, which leads to better catalytic performances.

Carbon-Supported Platinum Catalysts: Influence of Activation Treatment of a Synthetic Carbon Support and of Metal Deposition in the Selective Liquid Phase Oxidation of Alcohols

P. Korovchenko, C. Donze, P. Gallezot and M. Besson
Institut de Recherches sur la Catalyse-CNRS, 2 Avenue Albert Einstein, 69626 Villeurbanne Cedex (France)
Pages: 577-582

Abstract >>
Oxidations of alcohols into carbonyl functionalities are key reactions in the synthesis of fine chemicals. The need to substitute stoichiometric oxidations (using mineral oxidants) with "green" oxidations using benign oxidizing agents like molecular oxygen or hydrogen peroxide has been often emphasized. Supported noble metal catalysts, e.g. Pd/C or Pt/C are known to catalyse the oxidation of alcohols in the presence of molecular oxygen. It was previously reported that benzyl alcohol (Bzol) can be very selectively oxidized to benzaldehyde (Bzal) in dioxane, whereas the use of a 50/50 mixture of dioxane and alkaline aqueous solution yielded benzoic acid (Bzoic) by further oxidation of Bzal. In this work, we examined the effect of the activation treatment of the synthetic carbon and of the method of deposition of the metal on the characteristics of the supported metallic catalyst and its activity in this reaction. The highest dispersion and best catalytic performances were obtained by impregnation with hexachloroplatinic acid of a CO2 activated carbon.

Towards Large Scale Production of CNF for Catalytic Applications

I. Kvande, Z. Yu, T. Zhao, M. Rnning, A. Holmen and D. Chen
Department of Chemical Engineering, Norwegian University of Science and Technology, NTNU, N-7491 Trondheim (Norway)
Pages: 583-589

Abstract >>
A systematic investigation of carbon nanotubes (CNT) and nanofibre (CNF) growth in terms of structures of carbon nanomaterials and growth rates by chemical vapour deposition is summarized. Different catalysts such as unsupported Fe3O4 and supported Ni, Fe and NiFe catalysts and different carbon sources such as CO, CO/H2, CH4/H2, C2H6/H2 and C2H4/CO/H2 have been applied. This short review has been addressed to identify the principles for controlled synthesis of carbon nanotube or nanofibre with well-defined structures. The production of relatively high yields of defined structures is obtained. The Ni catalyst produces almost exclusively fishbone CNFs, while the supported Fe catalyst produces multiwall CNTs (MWCNTs). The NiFe catalyst can give a structure intermediate of the two. Unsupported Fe3O4 results in the platelet structure. The diameter of the produced structures holds information on the growth mechanism. The diameters of the MWNTs are always smaller than the growth catalyst particles, while the fishbone CNFs always have larger diameter than the growth catalyst. The structure and growth rate reflect the different reactivity of the metals and the dependence on surface orientation of the catalyst particles. Higher temperature and lower partial pressure yield smaller diameter MWNTs with fewer walls and a larger inner hollow core. The space velocity and thereby the H2 partial pressure in the reactor has been identified as the most important parameter for scale-up of the reactor.

Novel Carbon Based Catalysts for the Reduction of NO with Coke Petroleum Ashes as Active Phase: Synthesis and Characterisation

M. J. Lzaro, A. Boyano, M. E. Glvez, E. Garca-Bordej and R. Moliner
Instituto de Carboquimica CSIC, Miguel de Luesma Castn 4, 50018 Zaragoza (Spain)
Pages: 591-597

Abstract >>
Carbon-based catalysts in powder, briquette and monolith forms have been prepared. Powder and briquette samples have been obtained from low-rank coal whereas monolith samples were prepared by coating cordierite monoliths with a blend of two polymers, namely, furan resin and polyethylene glycol. Vanadium was impregnated in these carbon-based catalysts by equilibrium adsorption using the ashes of a petroleum coke (PCA) as precursor and they were tested in the SCR of NO at low temperature. PCA contains around 23%V, 3 % Fe and 3 % Ni among other transition metals and this use is an undeniable good way for its revalorisation. As-prepared catalysts have demonstrated a considerable efficiency which was enhanced by pre-oxidizing treatments and an increase of vanadium loading. The presence of oxygen surface functionalities is of key importance to achieve an adequate distribution and fixation of the active phase while an excess in vanadium loading can even cause pore blockage decreasing the total efficiency. External diffusion and pressure drop coefficients were calculated for the three kinds of catalysts. As expected, powder catalyst shows the highest pressure drop while briquette and monolith samples show lower pressure drop values with no sign of diffusion limitations. For this reason, these structurated catalysts are considered to be more suitable for industrial applications.

XPS Study of Carbon Films on the Pt(III) Surface obtained by high temperature decomposition of methane and ethylene

E. M. Pazhetnov and A. I. Boronin
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,
Pr. Akademika Lavrentyeva 5, Novosibirsk 630090 (Russia)
Pages: 599-603

Abstract >>
The carbon films grown on Pt(III) surface by the high temperature catalytic decomposition of methane and ethylene were investigated with aid of X-ray photoelectron spectroscopy (XPS). It was observed that photoelectron spectra of carbon films depend on the hydrocarbon used as a reagent. It was shown that in case of methane used as the reagent the flat graphite films are deposited on the Pt(III) surface while ethylene or ethylene/methane mixture stimulates the carbon films distortion resulting in curved fullerites/ like structures. The formation of curved carbon films occurs through the formation of flat graphenes as the intermediate structures. It was determined that this topographic transition is reversible and has dynamic character depending on the crystal temperature and ethylene presence in the gas phase. The role of the diffusion-segregation phenomenon of carbon atoms in the formation of the curved films was established.

Preparation and Characterisation of Dispersed Palladium Catalysts Supported on Carbon Previously Treated with Different strong oxidants

E. Santacesaria, M. Cozzolino, V. Balato, R. Tesser, M. Di Serio and F. Ruffo
University of Naples "Federico II", Dept. of Chemistry, Naples Industrial Chemistry Laboratory (NICL),
Complesso M. te S. Angelo, Via Cintia 4, 80126 Naples (Italy)
Pages: 605-611

Abstract >>
Dispersed palladium catalysts supported on carbon were prepared using different strong oxidants for preliminary treatment of the support. The surface properties of carbon and its ability to give place to highly dispersed Pd were discussed. Oxidative pre-treatment was shown to promote the dispersion significantly increasing the catalytic activity.

Optimization of Decalin/Catalyst Ratio in the Dehydrogenation of Decalin over Pt/C Catalysts via Experiment Design

D. Sebastin, E. Garca-Bordej, L. Calvillo, M. J. Lzaro and R. Moliner
Instituto de Carboqumica (C.S.I.C.), Miguel de Luesma Castn 4, 50018 Zaragoza (Spain)
Pages: 613-618

Abstract >>
We have supported platinum on a commercial activated carbon with different loadings. The as-prepared catalyst has been used for the dehydrogenation of decalin in a batch-type reactor under boiling and refluxing conditions. The impact of some variables such as temperature, % Pt loading and decalin/catalyst ratio was studied using experimental design tools. The experiments carried out enable us to find the decalin to catalyst ratio which led to the best catalytic performance in our system.

Carbon Aerogels as Catalyst Supports

M. Stolarski, K. Brodzik, J. Walendziewski, R. Luny and E. Broniek
Wroclaw University of Technology, Faculty of Chemistry,
Department of Fuels Chemistry and Technology, Ul. Gdaska 7/9, 50-344 Wroclaw (Poland)
Pages: 619-624

Abstract >>
Influence of the process parameters on porous structure of monolithic and spherical resorcinol-formaldehyde (RF) carbon aerogels prepared by supercritical acetone and carbon dioxide drying of alcogels, followed by carbonization is presented. The prepared organic RF aerogels were carbonized at 600 oC to form carbon aerogels and their porous structure was characterized by nitrogen adsorption. It was stated that synthesis parameters of RF organic aerogels (catalyst type, gel curing time, R/C ratio, resorcinol concentration in water) and drying method (low- or high-temperature supercritical drying) strongly influence textural parameters of the final carbon aerogels. Application of KOH in RF aerogel preparation allows obtaining carbon aerogels of the most advantageous parameters irrespective of the used drying method. Elongation of curing time of RF gels results in an increase in specific surface area and total pore volume of the carbon aerogels obtained both in the course of low- and high-temperature drying. Low-temperature supercritical drying of RF aerogels gives carbon materials of more advantageous texture parameters in comparison to carbon aerogels obtained in high-temperature supercritical drying.