References of "Pirard, Jean-Paul"
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See detailCaractérisation électrochimique de catalyseurs Pt/xérogel de carbone et Pt/aérogel de carbone
Job, Nathalie ULg; Maillard, F.; Marie, J. et al

Conference (2008, March 31)

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See detailIron(III) species dispersed in porous silica through sol-gel chemistry
Heinrichs, Benoît ULg; Rebbouh, Leila; Geus, John W et al

in Journal of Non-Crystalline Solids (2008), 354(2-9), 665-672

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore ... [more ▼]

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore width distributions. The nature of the iron species obtained has been examined in detail by UN-visible and Mossbauer spectroscopy, and magnetic, transmission electron microscopy, and X-ray diffraction studies. There is no evidence for the presence of any ordered iron(III) oxides in the samples but all three contain two types of iron species, specifically paramagnetic high-spin iron(III) ions isolated in silica and iron(III) containing nanoparticles with a broad width distribution centered on 1.5 nm, nanoparticles that contain antiferromagnetically coupled clusters of a few ligated bridged iron(III) ions. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailFormation mechanism of Y-junctions in arrays of multi-walled carbon nanotubes
Zilli, Dario; Blacher, Silvia ULg; Cukierman, Ana Lea et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2008), 327(1-3), 140-143

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 of metal particles during the tip-growth of the tubes. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailEffect of the counter-ion of the basification agent on the pore texture of organic and carbon xerogels
Job, Nathalie ULg; Gommes, Cédric ULg; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2008), 354(40-41), 4698-4701

Organic and carbon xerogels were prepared by polycondensation of resorcinol with formaldehyde in water, followed by evaporative drying and, eventually, pyrolysis. The pH of the precursor's solution was ... [more ▼]

Organic and carbon xerogels were prepared by polycondensation of resorcinol with formaldehyde in water, followed by evaporative drying and, eventually, pyrolysis. The pH of the precursor's solution was fixed at 6.0 in all cases by adding various hydroxides as basification agent. Three alkali metal hydroxides (LiOH, NaOH and KOH) and three alkaline earth metals hydroxides (Ca(OH)(2), Ba(OH)(2), Sr(OH)(2)) were used. It was found that the pore texture of the organic and carbon xerogels is totally independent on the cation size, but depends on the charge and concentration of the counter-cation. Indeed, the pore size of the alkaline earth metal loaded samples is larger than that of the alkali metal-doped xerogels. As a matter of fact, to reach the same initial pH, the concentration in alkali metal hydroxide must be twice that of the alkaline earth metal base. The effect of ions on the pore texture was thus attributed to electrostatic effects on the microphase separation process that occurs prior to gelation. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailOptimization of experimental procedure and statistical data treatment for kinetics of ethylene hydrogenation on a copper-magnesia catalyst
Pirard, Sophie ULg; Heinrichs, Benoît ULg; Heyen, Georges ULg et al

in Chemical Engineering Journal (2008), 138(1-3), 367-378

This study is an example of practical application of kinetic data treatment for simultaneous model discrimination and parameter estimation. The study is applied to the hydrogenation of ethylene on a ... [more ▼]

This study is an example of practical application of kinetic data treatment for simultaneous model discrimination and parameter estimation. The study is applied to the hydrogenation of ethylene on a copper-magnesia catalyst and brings a deepened analysis about the experimental strategy by comparing several alternative strategies using a priori and sequential experimental designs. The best model corresponds to a Langmuir-Hinshelwood mechanism with non-competing adsorption of hydrogen and ethylene and where the rate-determining step is either the addition of molecularly adsorbed hydrogen or the addition of the second atom of hydrogen adsorbed dissociatively. Furthermore, the important question of knowing in practice how many designs and how many measurements per design are actually necessary to determine accurate kinetic and physico-chemical parameters, is addressed. A data correction procedure is also presented that takes catalyst deactivation into account. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailMicrowave drying as an effective method to obtain porous carbon xerogels
Zubizarreta, Leire; Arenillas, Ana; Menendez, J. A. et al

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 ▲]

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See detailTailoring the textural properties of activated carbon xerogels by chemical activation with KOH
Zubizarreta, Leire; Arenillas, Ana; Pirard, Jean-Paul ULg et al

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 ▲]

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See detailCritical opalescence points to thermodynamic instability:relevance to small-angle X-ray scattering of resorcinol–formaldehyde gel formation at low pH
Gommes, Cédric ULg; Job, Nathalie ULg; Pirard, Jean-Paul ULg et al

in Journal of Applied Crystallography (2008), 41(4), 663-668

During the formation at low pH of resorcinol–formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a nonmonotonic intensity variation as a function of reaction ... [more ▼]

During the formation at low pH of resorcinol–formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a nonmonotonic intensity variation as a function of reaction time. The data are analyzed in terms of scattering by statistical fluctuations of polymer concentration, the amplitude of which is maximal close to the critical point for phase separation between polymer and solvent. The data do not carry any morphological information, but they unambiguously show that the driving force of the gel formation is a thermodynamic instability of the polymerizing solution. [less ▲]

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See detailThe microstructure of hybrid silica gels and its modification by evaporative and supercritical dryings
Gommes, Cédric ULg; Blacher, Silvia ULg; Pirard, Jean-Paul ULg et al

in Journal of Sol-Gel Science and Technology (2007), 44(3), 211-218

The effect of evaporative drying on the pore size of two series of hybrid silica gels is investigated by combining beam bending on the gels and mercury porosimetry on the aerogels and xerogels with ... [more ▼]

The effect of evaporative drying on the pore size of two series of hybrid silica gels is investigated by combining beam bending on the gels and mercury porosimetry on the aerogels and xerogels with transmission electron microscopy on the xerogels. It is shown that the shrinkage of the pores during drying is different in the two series: in one series the pores shrink proportionally to their volume, in the other the pores collapse until they all reach the same size. The experimental data enable us to discuss the relation between these two different behaviours and the different morphology of the two series of gels. [less ▲]

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See detailCarbon nanotubes synthesis by CCVD process : kinetic study on a Fe-Co/Al2O3 catalyst
Pirard, Sophie ULg; Douven, Sigrid ULg; Bossuot, Christophe et al

Poster (2007, August)

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See detailCarbon xerogels as catalyst supports
Job, Nathalie ULg; Léonard, Angélique ULg; Lambert, Stéphanie ULg et al

Poster (2007, August)

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See detailWater desorption isotherms of resorcinol-formaldehyde and carbon xerogels
Léonard, Angélique ULg; Escalona, I.; Job, Nathalie ULg et al

Poster (2007, July 15)

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See detailBranching, aggregation, and phase separation during the gelation of tetraethoxysilane
Gommes, Cédric; Goderis, Bart; Pirard, Jean-Paul ULg et al

in Journal of Non-Crystalline Solids (2007), 353(24-25), 2495-2499

Time-resolved small-angle X-ray scattering is used to follow in situ the structuring of silica sols and gels in various chemical conditions. The acid-catalyzed and base-catalyzed polymerizations of TEOS ... [more ▼]

Time-resolved small-angle X-ray scattering is used to follow in situ the structuring of silica sols and gels in various chemical conditions. The acid-catalyzed and base-catalyzed polymerizations of TEOS, as well as the copolymerization of TEOS with organically modified trialkoxysilanes, are followed. The analysis points to the diversity of the mechanisms that govern the structuring of the reacting solutions, and most notably to the important role of physical forces. (C) 2007 Elsevier B.V.All rights reserved. [less ▲]

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See detailRelevance of Spinodal Decomposition for Support Formation and Metal Dispersion in Cogelled Pd/SiO2 Catalysts
Gommes, Cédric ULg; Goderis, Bart; Pirard, Jean-Paul ULg

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 ▲]

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See detailWater desorption isotherms of resorcinol-formaldehyde and carbon xerogels
Léonard, Angélique ULg; Escalona, Ivonne; Job, Nathalie ULg et al

in The American Carbon Society (Ed.) Proceedings of Carbon 2007 (2007, July)

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See detailCarbon nanotubes synthesis by CCVD process : kinetic study on a Fe-Co/Al2O3 catalyst
Pirard, Sophie; Douven, Sigrid ULg; Bossuot, Christophe et al

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 ▲]

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See detailNon-destructive characterization of deer (Cervus Elaphus) antlers by X-ray microtomography coupled with image analysis
Léonard, Angélique ULg; Guiot, L. P.; Pirard, Jean-Paul ULg et al

in Journal of Microscopy-Oxford (2007), 225(Pt 3), 258-263

X-ray microtomography coupled with image analysis was tested as a non-destructive alternative method for the textural characterization of the trabecular part of deer antlers (Cervus Elaphus). As gas ... [more ▼]

X-ray microtomography coupled with image analysis was tested as a non-destructive alternative method for the textural characterization of the trabecular part of deer antlers (Cervus Elaphus). As gas adsorption and mercury intrusion cannot be applied on this soft and spongy material, its pore texture was, up to now, determined from histological sections that give only two-dimensional information. In this work, X-ray microtomography is used to scan entire or half pieces of antlers and three-dimensional image analysis is performed in order to assess the differences between samples collected at various antler locations. Results clearly show a porosity profile along the sample diameter. The pore size distribution is showed to be dependent on the sample original site. [less ▲]

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See detailCarbon nanotubes synthesis by the ethylene chemical catalytic vapour deposition (CCVD) process on Fe, Co, and Fe-Co/Al2O3 sol-gel catalysts
Tran, Kim Yên; Heinrichs, Benoît ULg; Colomer, Jean-François et al

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 ▲]

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See detailRheological determination of the sol-gel transition during the aqueous synthesis of resorcinol-formaldehyde resins
Job, Nathalie ULg; Panariello, Fabian; Crine, Michel ULg et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2007), 293(1-3), 224-228

The sol-gel transition of organic gels prepared by polycondensation of resorcinol (R) with formaldehyde (F) in presence of sodium carbonate (C) was monitored by small amplitude oscillatory measurements ... [more ▼]

The sol-gel transition of organic gels prepared by polycondensation of resorcinol (R) with formaldehyde (F) in presence of sodium carbonate (C) was monitored by small amplitude oscillatory measurements, at a single frequency. The gelation time (t(g)) was determined from the evolution of the storage (G) and loss (G") moduli versus time. The influence of two synthesis variables, the resorcinol/sodium carbonate ratio (R/C) and the synthesis temperature (7), was investigated. The gelation time was found to decrease with increasing synthesis temperature and decreasing R/C ratio. The apparent activation energy of the reactional system leading to the gelation, calculated from the gelation times obtained between 50 and 90 degrees C, was found to be close to 80 kJ mol(-1) and independent of the R/C ratio. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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