References of "Pirard, Jean-Paul"
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See detailSynthesis of transition metal-doped carbon xerogels by solubilization of metal salts in resorcinol-formaldehyde aqueous solution
Job, Nathalie ULg; Pirard, René ULg; Marien, José ULg et al

in Carbon (2004), 42(15), 3217-3227

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce ... [more ▼]

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce transition metal-containing carbons with tailored texture, various metallic salts were dissolved in the precursors solution. When necessary, a complexing agent (HEDTA or DTPA) was added to render the metal ions soluble. Ni, Fe and I'd loaded carbon xerogels were synthesized and their pore texture was studied after evaporative drying and after pyrolysis. The carbon texture was also studied with regard to the nature of the metal and the amount of complexing agent. The solubilization of transition metal salts in the resorcinol-formaldehyde aqueous solution does not prevent the texture regulation, even though this texture control is influenced: the limits of the pH interval leading to micro mesoporous carbon materials can slightly differ when a metal salt and/or a complexing agent are added. The pH range shift depends mainly on the amount and nature of the complexing agent, but also slightly on the nature of the metal ion. Nevertheless, the metal particles obtained are rather big (diameter > 15 nm). For catalytic applications, the metal dispersion must be enhanced, especially in the case of expensive metals. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMeasurement of shrinkage and cracks associated to convective drying of soft materials by X-ray microtomography
Léonard, Angélique ULg; Blacher, Silvia ULg; Marchot, Pierre ULg et al

in Drying Technology (2004), 22(7), 1695-1708

Traditionally, the measurement of shrinkage occurring during drying is performed by destructive or poorly accurate techniques such as volume displacement methods. Cracks detection and quantification are ... [more ▼]

Traditionally, the measurement of shrinkage occurring during drying is performed by destructive or poorly accurate techniques such as volume displacement methods. Cracks detection and quantification are realised either by destructive techniques or sophisticated but expensive nondestructive ones (NMR imaging). X-ray microtomography in combination with image analysis provides an accurate, nondestructive and easy to use technique to determine simultaneously shrinkage and crack extent. Results reported in this article concern drying of wastewater sludges whose management will become a real challenge in the years to come. These results show a clear relation between drying kinetics and crack development. This could be related to the development of internal diffusional limitations inducing moisture gradients and mechanical stresses leading to cracks formation. [less ▲]

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See detailBall milling effect on the structure of single-wall carbon nanotubes
Pierard, N.; Fonseca, Antonio; Colomer, Jean-François et al

in Carbon (2004), 42(8-9), 1691-1697

The vibratory mill is used to decrease the single-wall carbon nanotubes (SWNTs) length and to increase their specific surface area. Electron microscopy, Raman spectroscopy, X-ray diffraction and BET ... [more ▼]

The vibratory mill is used to decrease the single-wall carbon nanotubes (SWNTs) length and to increase their specific surface area. Electron microscopy, Raman spectroscopy, X-ray diffraction and BET measurements indicated that the optimum time of treatment seems to be 2 h. After that, the SWNTs quality decreases, with a complete disruption of the tubular structure leading to multi-layered polyaromatic carbon materials observed after 50 h. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailImprovement of metal dispersion in Pd/SiO2 cogelled xerogel catalysts for 1,2-dichloroethane hydrodechlorination
Lambert, Stéphanie ULg; Polard, Jean-François; Pirard, Jean-Paul ULg et al

in Applied Catalysis B : Environmental (2004), 50

The study of the influence of synthesis operating variables (nature and concentration of complexing silane, palladium percentage, temperatures of gelling, aging and vacuum drying of xerogels, molar ratio ... [more ▼]

The study of the influence of synthesis operating variables (nature and concentration of complexing silane, palladium percentage, temperatures of gelling, aging and vacuum drying of xerogels, molar ratio between the complexing silane and palladium, molar concentration of ammonia solution, and use of tetramethylammonium hydroxide as base instead of NH3) allows improving metal dispersion in Pd/SiO2 cogelled xerogel catalysts. The use of 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) or 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) to complex palladium in an ethanolic solution containing tetraethoxy si lane (TEOS) and an ammonia solution of 0.54 mol/l allows obtaining a Pd/SiO2 xerogel catalyst with a mean metal particle diameter of 2.4 nm located inside silica particles. Indeed, complexes Pd(EDA(E)S)(x)(n+) induce a nucleation mechanism because of their higher reactivity compared to the network-reagent (TEOS). Although metal particles are located inside the silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-dichloroethane hydrodechlorination over Pd/SiO2 catalysts mainly produces ethane and the specific hydrodechlorination rate per gram of palladium increases proportionally with palladium dispersion. Hydrodechlorination over Pd/SiO2 cogelled xerogel catalysts is a structure insensitive reaction with regard to the ensemble size concept. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailInfluence of the operating conditions on the production rate of multi-walled carbon nanotubes in a CVD reactor
Gommes, Cédric ULg; Blacher, Silvia ULg; Bossuot, C. et al

in Carbon (2004), 42(8-9), 1473-1482

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the ... [more ▼]

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the reaction rate to be inferred from the exhaust gas composition measurements. The tested reactor operating variables are the length and thickness of the catalytic bed, the total feed flow and the molar fraction of hydrocarbon in the feed. The results of the study are analyzed using well known reactor engineering models, which allows the origin of the observed physical limitations to be ascertained. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailPd-Ag/SiO2 and Pd-Cu/SiO2 cogelled xerogel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene
Lambert, Stéphanie ULg; Ferauche, Fabrice; Brasseur, Alain et al

Conference (2004)

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See detailImprovement of metal dispersion in Pd/SiO2 cogelled xerogel catalysts
Lambert, Stéphanie ULg; Polard, Jean-François; Ferauche, Fabrice et al

Poster (2004)

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See detailPalladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene - IV. Deactivation mechanism and regeneration
Heinrichs, Benoît ULg; Noville, Francis ULg; Schoebrechts, Jean-Paul ULg et al

in Journal of Catalysis (2003), 220(1), 215-225

The activity and selectivity of a 1.9% Pd-3.7% Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene have been followed in the course of time. The deactivation curves ... [more ▼]

The activity and selectivity of a 1.9% Pd-3.7% Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene have been followed in the course of time. The deactivation curves show two distinct periods: an initial period at the very beginning of catalyst operation, that is, during the first 20 operating hours, characterized by a sharp decrease of the rates of both reactions involved in the process (1,2-dichloroethane hydrodechlorination and undesired ethylene hydrogenation) and a second period, after the first 20 operating hours and investigated for more than 600 h, characterized by a clearly slower deactivation. During the initial period, the hydrodechlorination rate decreases less quickly than the hydrogenation rate and this results in a fast increase of ethylene selectivity which reaches a maximum at the end of this period. After the initial period, the hydrodechlorination rate decreases faster than the hydrogenation rate and this results in a slow decrease of ethylene selectivity. A comparison between the physico-chemical properties of the fresh catalyst and of the deactivated one suggests a deactivation mechanism by poisoning or coking of silver sites at the surface of the active Pd-Ag alloy particles whereas palladium sites would remain intact. The selectivity evolution during the second period, that is, after the very first operating hours, is in agreement with such a mechanism. However, the sharp ethylene selectivity increase during the initial operating hours suggests, in addition to the deactivation by silver sites disappearance, the presence of a further nonidentified phenomenon. The characterization of the catalyst after a regeneration treatment including an oxidation step followed by a reduction step shows that this treatment allows restoration near to the physico-chemical properties of the fresh catalyst. (C) 2003 Elsevier Inc. All rights reserved. [less ▲]

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See detailImage analysis of X-ray microtomograms of soft materials during convective drying
Léonard, Angélique ULg; Blacher, Silvia ULg; Marchot, Pierre ULg et al

in Journal of Microscopy (2003), 212(Pt 2), 197-204

X-ray microtomography is used to explore the textural evolution that soft materials undergo during a drying treatment. An original image processing algorithm is applied to vertical projections and ... [more ▼]

X-ray microtomography is used to explore the textural evolution that soft materials undergo during a drying treatment. An original image processing algorithm is applied to vertical projections and reconstructed cross-section images in order to quantify the texture at different stages of drying. Measurements are performed both on grey-level and on binary images. It is shown that X-ray microtomography is a very promising tool in the field of drying investigations. It can be used to determine internal moisture profiles, and to follow crack development and shrinkage in an accurate and non-destructive way. This information is crucial to validate drying models. Waste-water sludges are used as test materials to assess the validity of the proposed methodology. The management of these sludges, often including a drying stage, will become a challenge in the forthcoming years in accordance with environmental regulations. Samples collected in two waste-water treatment plants are investigated. Their analysis by X-ray microtomography brings to the fore two different drying behaviours, illustrating that sludge drying is a complex unit operation very sensitive to the way the material is produced. [less ▲]

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See detailCaractérisation par analyse d'images de nanotubes multiparois
Gommes, Cédric ULg; Masenelli-Varlot; Pirard, Jean-Paul ULg et al

Scientific conference (2003, October)

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See detailTime-resolved SAXS measurements of phase separation during silica gel formation
Gommes, Cédric ULg; Goderis, Bart; Pirard, Jean-Paul ULg et al

Poster (2003, October)

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See detailConvective drying of wastewater sludges: Influence of air temperature, superficial velocity and humidity on the kinetics
Léonard, Angélique ULg; Blacher, Silvia ULg; Marchot, Pierre ULg et al

in Pakowski, Zdzislaw (Ed.) X Drying Symposium, Lodz, 17-19 September 2003 (2003, September)

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