References of "Pirard, Jean-Paul"
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See detailImage analysis of X-ray microtomograms of soft materials during convective drying: 3D measurements
Léonard, Angélique ULg; Blacher, Silvia ULg; Marchot, Pierre ULg et al

in Journal of Microscopy-Oxford (2005), 218(Pt 3), 247-252

Drying dewatered sludge leads to a complex three-dimensional porous structure. Moreover, this operation is dependent on the way the material is processed. In this study, textural changes of sludge ... [more ▼]

Drying dewatered sludge leads to a complex three-dimensional porous structure. Moreover, this operation is dependent on the way the material is processed. In this study, textural changes of sludge extrudates submitted to convective drying are followed by a 3D image analysis of reconstructed X-ray microtomograms. To achieve this goal, two different wastewater sludges collected in wastewater treatment plant after the thickening step and dewatered in the laboratory are used. It is showed that the evolution of the 3D-crack ratio vs. the residual water content evolves following a hyperbolic law. The 3D opening crack size distribution reveals two different types of pore development, i.e. a continuous pore size evolution for one sludge and the sudden appearance of cracks for the other sludge. [less ▲]

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See detailHydrodechlorination of 1,2-dichloroethane on Pd-Ag catalysts supported on tailored texture carbon xerogels
Job, Nathalie ULg; Heinrichs, Benoît ULg; Ferauche, Fabrice et al

in Catalysis Today (2005), 102

Porous carbon xerogels synthesized in a previous study were investigated as catalysts supports. The support chosen was a micro-mesoporous carbon xerogel obtained from the pyrolysis of a resorcinol ... [more ▼]

Porous carbon xerogels synthesized in a previous study were investigated as catalysts supports. The support chosen was a micro-mesoporous carbon xerogel obtained from the pyrolysis of a resorcinol-formaldehyde resin whose synthesis variables were fixed at suitable values. Palladium and silver were deposited on this tailored texture carbon by co-impregnation using a solution of palladium and silver nitrates in nitric acid and water. Several catalysts were prepared with various Pd and Ag global contents, the latters being measured experimentally. Alloy particles, detected in all bimetallic samples, were studied by a combination of various techniques that enabled us to obtain their size as well as their bulk and surface composition. When present, the fraction of unalloyed silver was also calculated. The characterization data were related to the results of catalytic tests obtained for selective hydrodechlorination of 1,2-dichloroethane into ethylene. Results show that when the Ag content is too high, pure Ag particles are formed and the alloy composition remains constant. As a consequence, the surface composition of the alloy is constant as well and the catalytic tests lead to similar results. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailMicroporous and heterogeneous surface adsorption isotherms arising from Levy distributions
Brouers, François ULg; Sotolongo, O.; Marquez, F. et al

in Physica A: Statistical Mechanics and its Applications (2005), 349(1-2), 271-282

We show that for adsorption on heterogeneous and microporous surfaces, the Freundlich isotherm power-law exponent a is directly related to the Levy tail index of the distribution of the Langmuir parameter ... [more ▼]

We show that for adsorption on heterogeneous and microporous surfaces, the Freundlich isotherm power-law exponent a is directly related to the Levy tail index of the distribution of the Langmuir parameter b and to the expected value and the variance of the adsorption energy distribution. This allows us to view adsorption at low pressure in these systems as a rare event dominated phenomena. Based on this discussion, a generalized isotherm formulation is proposed and applied to the interpretation of recent data on activated carbons. (C) 2004 Elsevier B.V. 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

in Catalysis Today (2005), 100(3-4), 283-289

While 1,2-dichloroethane hydrodechlorination over pure palladium mainly produces ethane, increasing silver or copper content in bimetallic catalysts results in an increase in ethylene selectivity. The ... [more ▼]

While 1,2-dichloroethane hydrodechlorination over pure palladium mainly produces ethane, increasing silver or copper content in bimetallic catalysts results in an increase in ethylene selectivity. The specific consumption rate of 1,2-dichloroethane decreases when silver or copper loading increases. The turnover frequency, that is, the number of catalytic cycle per active site (palladium atom and its surrounding silver or copper atoms) and per second, seems to be independent of surface composition of alloy particles and 1,2-dichloroethane hydrodechlorination is insensitive to the atom's nature (silver or copper). (c) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailMoisture profiles determination during convective drying using x-ray microtomography
Léonard, Angélique ULg; Blacher, Silvia ULg; Marchot, Pierre ULg et al

in Canadian Journal of Chemical Engineering (2005), 83(1), 127-131

The knowledge of internal moisture profiles which develop during drying is essential for model validation purposes, but they are difficult to determine experimentally. This paper shows that X-ray ... [more ▼]

The knowledge of internal moisture profiles which develop during drying is essential for model validation purposes, but they are difficult to determine experimentally. This paper shows that X-ray microtomography, together with image analysis, provides an accurate, non destructive and easy to use technique to determine moisture profiles. Results reported concern the drying of wastewater sludges whose management is becoming a real environmental challenge. An analysis of the development of moisture gradients at the sample external wall shows an influence of drying operating conditions. Finally, mass diffusion coefficients are estimated from the knowledge of both the moisture gradients and the drying flux. [less ▲]

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See detailX-ray microtomography coupled with image analysis: a useful tool for 3D characterization of polymer foams
Blacher, Silvia ULg; Kerckhofs, Greet ULg; Caliberg, Cédric et al

in Proceedings of Imageries et polymères 2005 (2005)

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See detailOlefin cyclopropanation and insertion into O-H bonds mediated by copper(I) and palladium(II) covalently anchored to silica xerogels
Sacco, Luigi; Lambert, Stéphanie ULg; Pirard, Jean-Paul ULg et al

in Journal of Catalysis (2005), 232(1), 51-59

Copper(I) and palladium(II) ligated to pyrazolylpyridine hearing a tethered (trimethoxysilyl)propyl group in position 4 of the pyrazole ring were chemically bonded to silica via a sol-gel process. The ... [more ▼]

Copper(I) and palladium(II) ligated to pyrazolylpyridine hearing a tethered (trimethoxysilyl)propyl group in position 4 of the pyrazole ring were chemically bonded to silica via a sol-gel process. The textural properties of the materials (Specific Surface area, porous volume, and pore size distribution) were characterized by nitrogen adsorption-desorption isotherms, mercury porosimetry, and TEM analysis. The hybrid materials were tested as catalysts in olefin cyclopropanation and as potential chemoselective catalysts in the reaction with unsaturated alcohols (double bond versus -OH group), with ethyl diazoacetate as a carbene precursor, and compared with the corresponding homogeneous complexes. © 2005 Elsevier Inc. All rights reserved. [less ▲]

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See detailFormation and structural characteristics of Pd-Ag/SiO2 and Pd-Cu/SiO2 catalysts synthesized by cogelation
Lambert, Stéphanie ULg; Gommes, Cédric ULg; Alié, Christelle ULg et al

in Journal of Non-Crystalline Solids (2005), 351(52-54), 3839-3853

Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane ... [more ▼]

Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). After an extensive study of the influences of synthesis operating variables over structural characteristics of gels, highly dispersed bimetallic Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts were obtained. These samples are then composed of completely accessible Pd-Ag and Pd-Cu alloy crystallites with sizes of 2-3.5 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears also that the metal complex acts as a nucleation agent in the formation of silica particles. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailQualitative assessment of the purity of multi-walled carbon nanotube samples using krypton adsorption
Gommes, Cédric ULg; Noville, Francis ULg; Bossuot, Christophe et al

in Studies in Surface Science and Catalysis (2005), 160

Krypton is a subcritical vapour at the nitrogen boiling temperature. As such, its adsorption on crystalline surfaces leads to condensation steps, typical of type VI isotherms according to IUPAC, while its ... [more ▼]

Krypton is a subcritical vapour at the nitrogen boiling temperature. As such, its adsorption on crystalline surfaces leads to condensation steps, typical of type VI isotherms according to IUPAC, while its adsorption on rough surfaces is BET-like. Based on this property of krypton adsorption at 77 K, a methodology is proposed to determine the purity of carbon nanotubes samples. The method is tested on model samples obtained by mixing mechanically purified multi-walled carbon nanotubes with various amounts of the same catalyst as used for their synthesis. [less ▲]

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See detailNitrogen Adsorption on Silica Xerogels or the Odd Look of a t Plot
Gommes, Cédric ULg; Blacher, Silvia ULg; Pirard, Jean-Paul ULg

in Langmuir (2005), 21

Nitrogen adsorption in some silica xerogels leads to t plots that cannot be interpreted by the occurrence of capillary condensation or by the filling of micropores. Their particular appearance stems from ... [more ▼]

Nitrogen adsorption in some silica xerogels leads to t plots that cannot be interpreted by the occurrence of capillary condensation or by the filling of micropores. Their particular appearance stems from the unique columnar structure of these samples at the nanometer scale, by which the adsorbent surface has a positive curvature. A standard thermodynamic approach allows the phenomenon to be exploited to characterize the samples. [less ▲]

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See detailAssessment of the 3D Localization of Metallic Nanoparticles in Pd/SiO2 Cogelled Catalysts by Electron Tomography
Gommes, Cédric ULg; de Jong, Krijn; Pirard, Jean-Paul ULg et al

in Langmuir (2005), 21

The purpose of this study is to analyze the localization of palladium nanoparticles within their silica support, in two heterogeneous catalysts synthesized by the sol-gel process, with different metal ... [more ▼]

The purpose of this study is to analyze the localization of palladium nanoparticles within their silica support, in two heterogeneous catalysts synthesized by the sol-gel process, with different metal loadings. Electron tomography demonstrates that the palladium particles are localized deep inside the silica skeleton. The use of digital image analysis further shows that the dispersion of palladium is optimal in the sample with the lowest loading. The particles are regularly spaced in the middle of the silica skeleton, with a distance between them comparable to the diameter of the struts of silica. [less ▲]

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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 Drying Technology (2005), 23(8), 1667-1679

The influence of air temperature, velocity, and humidity during convective drying of two different sludges (A and B) is investigated through a 3 3 factorial design. For sludge A, a constant drying flux ... [more ▼]

The influence of air temperature, velocity, and humidity during convective drying of two different sludges (A and B) is investigated through a 3 3 factorial design. For sludge A, a constant drying flux period is observed, while sludge B is characterized by a long decreasing drying flux phase. A sensitivity analysis shows that temperature is the main operating parameter affecting the drying kinetics. Mass and heat transfer coefficients as well as water evaporation capacities are calculated from drying curves. Transfer coefficients are related to operating conditions through dimensionless relations. For both sludges, a linear relation is found between water evaporation capacity and the maximal measured drying flux. [less ▲]

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See detailCarbon aerogels, cryogels and xerogels: Influence of the drying method on the textural properties of porous carbon materials
Job, Nathalie ULg; Thery, Alexandre; Pirard, René ULg et al

in Carbon (2005), 43(12), 2481-2494

Carbon materials with tailored texture can be obtained from drying and pyrolysis of resorcinol-formaldehyde gels. The pore texture of both dried and pyrolyzed material depends on the drying process ... [more ▼]

Carbon materials with tailored texture can be obtained from drying and pyrolysis of resorcinol-formaldehyde gels. The pore texture of both dried and pyrolyzed material depends on the drying process. Several more or less expensive methods (supercritical drying, freeze-drying, evaporative drying) were tested in order to determine which process is the most suitable for the synthesis of a porous carbon with a definite texture. Supercritical drying leads to the highest pore volume and the widest texture range, but residual surface tensions and shrinkage are not avoided when the pore size is small or when the material density is low; this hampers to fix both the pore volume and the pore size easily. Monoliths are very difficult to obtain by freeze-drying, and the appearance of huge channels due to ice crystal growth at high dilution ratio hinders the fabrication of low density materials. Moreover, gels with small pores do not remain frozen throughout drying, which leads to surface tensions and shrinkage. Although generally replaced by more complicated techniques, evaporative drying is suitable when dense carbons are needed or when the only selection criterion is the pore size: all pore sizes are reachable, but this parameter is in this case strongly correlated to the pore volume. (C) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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