Microwave drying as an effective method to obtain porous carbon xerogels

in Journal of Non-Crystalline Solids (2008), 354(33), 4024-4026

Microwave drying was used to prepare resorcinol-formaldehyde aqueous gels, without performing any pretreatment, and to see whether it was possible to use this drying option to obtain porous carbon ... [more ▼]

Microwave drying was used to prepare resorcinol-formaldehyde aqueous gels, without performing any pretreatment, and to see whether it was possible to use this drying option to obtain porous carbon xerogels with controlled textural properties. By using microwave drying, the process for obtaining carbon gels is greatly simplified, textural properties are controlled likewise with other drying methods, but the time involved in the process is significantly reduced and no pretreatment is necessary. Therefore, microwave drying could help to simplify the carbon xerogels synthesis and reduce the associated costs. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

Tailoring the textural properties of activated carbon xerogels by chemical activation with KOH

in Microporous & Mesoporous Materials (2008), 115(3), 480-490

Resorcinol-formaldehyde xerogels synthesised with different resorcinol/sodium carbonate molar ratios were chemically activated either after drying or after drying and pyrolysis, using potassium hydroxide ... [more ▼]

Resorcinol-formaldehyde xerogels synthesised with different resorcinol/sodium carbonate molar ratios were chemically activated either after drying or after drying and pyrolysis, using potassium hydroxide. It was found that organic (i.e. dried) and carbon (i.e. pyrolysed) xerogels behave differently when subjected to chemical activation. In the case of carbon xerogels, the increase in the microporosity takes place without any significant modification to the meso/macroporosity formed during the synthesis step, leading to micromesoporous or micro-macroporous materials with a larger micropore volume. Furthermore, control of the microporosity is possible because its development depends on the amount of KOH used. However, when organic xerogels are activated, mainly microporous materials with BET specific surface areas of up to 2000 m(2) g(-1) are obtained, there hardly remaining any of the meso/macroporosity formed during the gel synthesis. Thus, the combination of different synthesis conditions and chemical activation with potassium hydroxide allows the textural properties of carbon xerogels to be tailored at both micropore and meso/macropore levels. (c) 2008 Elsevier Inc. All rights reserved. [less ▲]

Formation mechanism of Y-junctions in arrays of multi-walled carbon nanotubes

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2008), 327

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode ... [more ▼]

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode corresponding to the branches and the other mode to the trunk of the Y-junctions. The analysis of the micrographs shows that the junctions form via the merger ofmetal particles during the tip-growth of the tubes. [less ▲]

Carbon nanotubes synthesis by CCVD process : kinetic study on a Fe-Co/Al2O3 catalyst

Poster (2007, August)

Water desorption isotherms of resorcinol-formaldehyde and carbon xerogels

Poster (2007, July 15)

Relevance of Spinodal Decomposition for Support Formation and Metal Dispersion in Cogelled Pd/SiO2 Catalysts

in Journal of Physical Chemistry C (2007), 111

The structure formation of cogelled Pd/SiO2 catalysts is followed in situ at the nanometer scale using timeresolved small-angle X-ray scattering (SAXS). The SAXS patterns are analyzed in terms of a ... [more ▼]

The structure formation of cogelled Pd/SiO2 catalysts is followed in situ at the nanometer scale using timeresolved small-angle X-ray scattering (SAXS). The SAXS patterns are analyzed in terms of a reaction-induced spinodal decomposition that is responsible for the formation of the silica support and most likely for the metal dispersion as well. The results are discussed in the light of recent electron tomography characterizations of the catalysts. The latter technique reveals regularity in the metal dispersion, the origin of which is likely to be the very occurrence of a spinodal phase separation. [less ▲]

Carbon nanotubes synthesis by CCVD process : kinetic study on a Fe-Co/Al2O3 catalyst

in Carbon (2007), 45(6), 1167-1175

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high ... [more ▼]

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high temperature using ethylene decomposition to solid carbon and gaseous hydrogen. The study uses a mass spectrometer that allows reaction rate to be inferred from the exhaust gas composition measurements. The aim is to obtain a better understanding of the elementary steps involved in the production of carbon nanotubes so as to derive phenomenological kinetic models in agreement with experimental data. The best models assume the elimination of the first hydrogen atom from adsorbed ethylene as rate determining step and involve a hydrogen adsorption weak enough to be neglected. It was proved that hydrogen partial pressure has no influence on initial reaction rate of carbon nanotube synthesis with the catalyst used for this study. Activation energy and ethylene adsorption enthalpy were found to be equal to around 130 and - 130 kJ mol(-1), respectively. (C) 2007 Elsevier Ltd. All rights reserved. [less ▲]

Carbon nanotubes synthesis by the ethylene chemical catalytic vapour deposition (CCVD) process on Fe, Co, and Fe-Co/Al2O3 sol-gel catalysts

in Applied Catalysis A : General (2007), 318

The production of carbon nanotubes by the chemical catalytic vapour deposition, CCVD, process was examined over iron, cobalt, and a mixture of iron and cobalt supported on alumina catalysts synthesized by ... [more ▼]

The production of carbon nanotubes by the chemical catalytic vapour deposition, CCVD, process was examined over iron, cobalt, and a mixture of iron and cobalt supported on alumina catalysts synthesized by a one step sol-gel process. The catalysts were synthesized from several metal precursors, iron nitrate, cobalt and iron acetylacetonate, and cobalt acetate. Ethylene was used as the carbon source. The Co/Al2O3 catalysts showed better activity and selectivity in carbon nanotubes synthesis than Fe/Al2O3 and Fe-Co/Al2O3 catalysts. The carbon deposit was found by TEM analysis to be rich in carbon nanotubes in the case of Co/Al2O3 but to be very poor in the case of the Fe-Co/Al2O3 catalysts. The catalysts were characterized by TEM, XRD, and nitrogen adsorption. It was shown that iron and cobalt are in oxide form. Metal-support interactions and metal oxide particle size are influenced by the nature of the precursor and this nature is an important factor for the activity and selectivity of the catalysts. Moreover, a correlation has been found between the metal oxide particle sizes, the diameter of the carbon nanotubes, and the catalytic activity. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Investigation of the preparation and activity of gold catalysts in the total oxidation of n-hexane

in Applied Catalysis B : Environmental (2007), 70(1-avr Sp. Iss. SI), 406-416

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition-precipitation is discussed through ... [more ▼]

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition-precipitation is discussed through comparison of the samples prepared by this method and others prepared by anion adsorption method. The influence of the pH and of the origin of TiO2 support used are additionally addressed. The difference of gold dispersion observed between the two methods is attributed to a difference of mobility of the gold precursors during the thermal treatment rather than to a difference of dispersion over the uncalcined samples. The mechanism of gold deposition-precipitation actually involves the reactions of gold hydroxy-chloride species with the surface. Another pan of the work, thus, concerned the use of the deposition-precipitation method to prepare a Au/MnO2 catalyst. It is shown that the activity of gamma-MnO2 is directly proportional to its surface area and that the deposition-precipitation procedure decreases the surface and activity of MnO2. However, the deposition of gold allows to avoid a too deep sintering of gamma-MnO2 and, thus, helps to somehow preserve its activity. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Analysis of kinetic models of multi-walled CNT synthesis

in Carbon (2007), 45(15), 3050-3052