References of "Pirard, Jean-Paul"
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See detailCharacterisation of silica low-density xerogels in presence of additives by image analysis and nitrogen adsorption-desorption
Blacher, Silvia ULg; Alié, Christelle ULg; Gommes, Cédric ULg et al

in Characterization of Porous Solids VI (2002)

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron ... [more ▼]

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron microscopy (TEM) micrographs and nitrogen adsorption-desorption experiments. To perform image analysis, novel image processing has been developed on the basis of classical signal treatment and mathematical morphology theory. The obtained results have been correlated with classical and fractal interpretation of nitrogen adsorption-desorption measurements. [less ▲]

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See detailSingle step synthesis of metal catalysts supported on porous carbon with controlled texture
Job, Nathalie ULg; Ferauche, Fabrice; Pirard, René ULg et al

in Studies in Surface Science and Catalysis (2002)

This paper presents an original preparation method of metal catalysts supported on carbon porous material [1]. Carbon porous materials can be synthesised by evaporative drying and pyrolysis of aqueous ... [more ▼]

This paper presents an original preparation method of metal catalysts supported on carbon porous material [1]. Carbon porous materials can be synthesised by evaporative drying and pyrolysis of aqueous resorcinol-formaldehyde gels whose operating, variables are correctly chosen. The porous texture of these materials is mainly controlled by the precursor solution pH. Texture analysis shows that it is possible to tailor the morphology of these materials : indeed, micro-macroporous, micro-mesoporous, microporous or non porous materials can be obtained by varying the pH value in a narrow pH interval. This texture control is slightly influenced by the introduction of a metal in the gel : the limits of the pH interval can slightly differ when a metal salt is added to the resorcinol-formaldehyde aqueous solution. Carbon supported nickel and palladium catalysts prepared by this method have proven to be active for ethylene hydrogenation. [less ▲]

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See detailThe role of the main silica precursor and the additive in the preparation, of low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2002), 311(3), 304-313

The incorporation of an additive during sol-gel synthesis reduces shinkage during ambient drying. The following additives have been studied: 3-,(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3 ... [more ▼]

The incorporation of an additive during sol-gel synthesis reduces shinkage during ambient drying. The following additives have been studied: 3-,(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltriethoxysilane (AES) and 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) and the main silica precursors were tetraethylorthosilicate (TEOS) and tetrapropylorthosilicate (TPOS). When the additive contains methoxy groups (EDAS), it acts as a nucleation agent of the silica particles and exactly the same properties (pore volume, specific surface area, particle and aggregate size) are obtained whether the main reagent is TEOS or TPOS. The nucleation mechanism is based on the difference in reactivity between additive and main reagent. In case of nucleation by the additive, the nucleation agent fixes the properties whatever the main silica precursor is. When both the additive and the main reagent contain ethoxy groups (series AES-TEOS and EDAES-TEOS), there is no nucleation mechanism by the additive, and the silica particle size remains nearly constant. With less reactive main reagent (series AES-TPOS and EDAES-TPOS), pore volumes up to 17 cm(3)/g have been obtained with pore sizes up to nearly 10 pm and very big particles (similar to100 nm). The absence of nucleation by the additive for the couples AES-TPOS and EDAES-TPOS could be due to the fact that the difference in reactivity between ethoxy groups and propoxy groups is not sufficient to initiate the nucleation mechanism by the additive. In the absence of nucleation by the additive, the main reagent plays a role: highly porous materials with very large p. ores are prepared with TPOS. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailTexture characterization of ultramacroporous materials using non-destructive methods
Blacher, Silvia ULg; Maquet, Véronique; Léonard, Angélique ULg et al

in Studies in Surface Science and Catalysis (2002), 158

Image analysis, impedance spectroscopy and X-ray microtomography have been used as non-destructive methods in order to characterize ultramacroporous materials (pore width > 1 mum). These methods are used ... [more ▼]

Image analysis, impedance spectroscopy and X-ray microtomography have been used as non-destructive methods in order to characterize ultramacroporous materials (pore width > 1 mum). These methods are used to investigate the texture of different kinds of materials, i.e., highly oriented polylactide (PLA) foams prepared by freeze-drying, isotropic polyolefin foams prepared by thermal degradation of a chemical foaming agent and convective heat dried wastewater sludges. The image analysis of SEM micrographs recorded at different magnifications gave information on the pore size distribution and pore morphology. Impedance spectroscopy was used to investigate the transport properties of the three-dimensional porous matrices by measurement of the water ionic conduction. Finally, 3D image reconstruction from 2D cross-sections obtained by X-ray microtomography allowed visualizing the pore structure. [less ▲]

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See detailSynthesis of Pd/SiO2, Ag/SiO2 and Cu/SiO2 catalysts by sol-gel process : study of metal dispersion and nucleation phenomenon
Lambert, Stéphanie ULg; Ferauche, Fabrice; Heinrichs, Benoît ULg et al

in CD-ROM of full abstracts of the 2nd International Conference on Silica Science and Technology, SILICA 2001 (4 p.) (2001, September 03)

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See detailStudy of the sugar ingot flow-patterns in the Notre-Dame Refinery silo in Oreye
Job, Nathalie ULg; Dardenne, A.; Pirard, Jean-Paul ULg

Poster (2001, May 29)

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See detailStudy of the sugar ingot flow-patterns in the Notre-Dame Refinery silo in Oreye
Job, Nathalie ULg; Dardenne, A.; Pirard, Jean-Paul ULg

in Proceedings of the First International Congress on Tracers and Tracing methods (2001)

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See detailMercury porosimetry applied to porous silica materials: successive buckling and intrusion mechanisms
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2001), 187

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between ... [more ▼]

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between the two mechanisms is characteristic of the tested material and allows to compute the buckling constant used to determine the pore size distribution in the compaction part of the experiment. The analysis of the mercury porosimetry data of a low-density xerogel wrapped in a tight membrane by the buckling law (intrusion is prevented and the sample is crushed during the whole porosimetry experiment) leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. This experiment confirms the validity of the use of the buckling law. The behaviour of the low-density xerogels can be related to one of their morphological characteristics. As the size of the aggregates of silica particles increases, the strength towards crushing increases and the change of mechanism from crushing to intrusion takes place at a lower pressure. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailImage analysis, impedance spectroscopy and mercury porosimetry characterisation of freeze-drying porous materials
Blacher, Silvia ULg; Maquet, Véronique; Pirard, René ULg et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2001), 187-188

Image analysis and impedance spectroscopy have been used as potential tools for the characterization of the texture of ultramacroporous PLA foams prepared by freeze-drying. It has been shown that these ... [more ▼]

Image analysis and impedance spectroscopy have been used as potential tools for the characterization of the texture of ultramacroporous PLA foams prepared by freeze-drying. It has been shown that these two techniques actually provide valuable information on the structure of this material. They are complementary to mercury porosimetry, which does not allow morphological details to be distinguished. Image analysis of SEM micrographs of transverse cross-sections at two different magnifications gave information on both the macroporosity (1 μm < width < 10 μm) and ultramacroporosity (width > 10 μm). Impedance spectroscopy was used to investigate the transport properties of the three-dimensional porous matrices by measurement of ionic conduction [less ▲]

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See detailThe use of additives to prepare low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Lecloux, A. J. et al

in Journal of Non-Crystalline Solids (2001), 285

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See detailMass transfer in low-density xerogel catalysts
Heinrichs, Benoît ULg; Pirard, Jean-Paul ULg; Schoebrechts, Jean-Paul

in AIChE Journal (2001), 47(8), 1866-1873

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts ... [more ▼]

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts. The catalyst consists of active Pd-Ag nanocrystallites trapped inside elementary 20 nm microporous silica particles arranged in larger aggregates, which constitute the macroscopic pellet. To reach active sites, reactants must first diffuse through large pores located between aggregates of SiO2 Particles and then through smaller pores located between those elementary particles inside the aggregates. Finally, they, diffuse through micropores located inside silica particles. Diffusion in such a "funnel" structure cannot be described assimilating the pellet to a pseudo-continuum. Diffusion should be examined carefully at three levels of decreasing size: the macroscopic pellet, the aggregate of silica particles, and the elementary silica particle. This approach shows that cogelled xerogel catalysts have remarkable mass-transfer properties. [less ▲]

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See detailPalladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene III. Kinetics and reaction mechanism
Heinrichs, Benoît ULg; Schoebrechts, Jean-Paul; Pirard, Jean-Paul ULg

in Journal of Catalysis (2001), 200(2), 309-320

The kinetics of selective hydrodechlorination of 1,2-dichloro-ethane into ethylene over a Pd-Ag/SiO2 catalyst is studied. Kinetic data at 573, 596, and 647 K have been obtained by means of experimental ... [more ▼]

The kinetics of selective hydrodechlorination of 1,2-dichloro-ethane into ethylene over a Pd-Ag/SiO2 catalyst is studied. Kinetic data at 573, 596, and 647 K have been obtained by means of experimental designs in the space of the partial pressures of the four components influencing kinetics, that is, 1,2-dichloroethane, hydrogen, ethylene, and hydrogen chloride. One model among the numerous ones examined allows us to represent correctly the experimental data. Ii: corresponds to the following mechanism: dechlorination of 1,2-dichloroethane into ethylene occurs on silver through dissociative adsorption with successive breaking of the two C-Cl bonds and desorption of C2H4. Thanks to its activation power of hydrogen by dissociative chemisorption, palladium present at the surface of the alloy supplies hydrogen atoms for regeneration of the chlorinated silver surface into metallic silver. The presence of hydrogen adsorbed on Pd also causes the undesired ethylene hydrogenation leading to a loss of olefin selectivity. (C) 2001 Academic Press. [less ▲]

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See detailPreparation of low-density xerogels by incorporation of additives during synthesis
Alié, Christelle ULg; Ferauche, Fabrice; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2001), 289(1-3), 88-96

Low-density xerogels were prepared by incorporation of an additive to alcogels prior to gelation. The additives studied are 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3 ... [more ▼]

Low-density xerogels were prepared by incorporation of an additive to alcogels prior to gelation. The additives studied are 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltrimethoxysilane (AMS), propyltrimethoxysilane (PMS), tetramethylorthosilicate (TMOS) and 3-aminopropyltriethoxysilane (AES) using tetraethylorthosilicate (TEOS) as main silica precursor. Samples were also prepared with EDAS as additive and TMOS as main silica reagent. When the additive contains methoxy groups, it reacts first, forms nuclei on which the main reagent TEOS reacts to form the silica particles. The nucleation mechanism by the additive occurs only in case of a difference of reactivity between additive and main silica precursor. The other group of the additive (amine, alkyl group, ...) influences only the gelation time. In case of ethoxy groups (series AES/TEOS) or methoxy groups (series EDAS/TMOS) for both additive and main reagent, there is no nucleation by the additive. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailMercury porosimetry: applicability of the buckling-intrusion mechanism to low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2001), 292(1-3), 138-149

Mineral materials can be either crushed or invaded by mercury during mercury porosimetry experiments. It has been shown here that many low-density xerogels exhibit the two volume variation mechanisms ... [more ▼]

Mineral materials can be either crushed or invaded by mercury during mercury porosimetry experiments. It has been shown here that many low-density xerogels exhibit the two volume variation mechanisms successively, compaction followed by intrusion. when submitted to mercury porosimetry and that a unimodal pore size distribution can be obtained by applying Pirard's collapse model below the pressure of transition P-1 and Washburn's intrusion theory above P-t. To confirm the validity of the use of the buckling law, one low-density xerogel was wrapped in a tight membrane (intrusion is prevented and the sample is crushed during the whole porosimetry experiment). The analysis of the mercury porosimetry data of the wrapped sample by the buckling law leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. The position of P-t is characteristic of the tested material: when submitted to mercury pressure. aerogels and low-density xerogels only collapse in case of very small aggregates whereas they are crushed and then intruded in case of larger silica aggregates. The fact that compacted slabs of monodisperse non-aggregated silica spheres (of the same size range as the xerogels and aerogels) show only intrusion during mercury porosimetry experiments implies that the particles need to be aggregated so that the compaction mechanism takes place. The position of the change of mechanism from crushing to intrusion is not directly related to the size of the elementary particles but is linked to the size of the aggregates of silica particles. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailCharacterization of porous polylactide foams by image analysis and impedance spectroscopy
Maquet, Véronique; Blacher, Silvia ULg; Pirard, René ULg et al

in Langmuir (2000), 16(26), 10463-10470

The texture of highly porous polylactide foams prepared by freeze-drying of poly-L-lactide (L-PLA) and poly-DL-lactide (DL-PLA) solutions of various concentrations was investigated by two novel ... [more ▼]

The texture of highly porous polylactide foams prepared by freeze-drying of poly-L-lactide (L-PLA) and poly-DL-lactide (DL-PLA) solutions of various concentrations was investigated by two novel methodologies, image analysis and impedance spectroscopy. Image analysis of scanning electron micrographs of transverse cross-sections at two different magnifications gave information on both the macroporosity (1 mum < width 10 <mu>m) and ultramacroporosity (width > 10 mum). Impedance spectroscopy was used to investigate the transport properties of the three-dimensional porous matrices by measurement of ionic conduction. Image analysis showed that: (a) the macroporosity, which mainly contributes to porosity, is independent of the sample composition; (b) when the concentration of the polymer solution is increased, the density of the ultramacropores decreases and their average diameter increases; (c) the distribution of the ultramacropores is more homogeneous in the semicrystalline L-PLA. foams than in the amorphous DL-PLA counterparts, in which the ultramacropores tend to make clusters. The dielectric properties changed at low frequency, in relation to modifications in the ultramacroporosity. Ultramacropores of the L-PLA foams were found to be more open and more sensitive to the concentration of the polymer solutions compared with DL-PLA. Expectedly, the mechanical properties of the PLA foams changed with the structure of the ultramacroporous network. These results encourage further investigations on the texture of porous supports, to collect pertinent information on the physical macro- and ultramacroenvironment in which cells will reside. [less ▲]

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See detailHydrodechlorination of 1,2-dichloroethane into ethylene : selectivity of Pd-Ag alloys of known surface composition
Heinrichs, Benoît ULg; Lambert, Stéphanie ULg; Schoebrechts, Jean-Paul et al

in Heterogeneous Catalysis, Proceedings of the 9th International Symposium (2000, September 23)

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