References of "Pirard, Jean-Paul"
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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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See detailProcess for the preparation of a catalyst and its use for the conversion of chloroalkanes into alkenes containing less chlorine
Delhez, Patrice; Heinrichs, Benoît ULg; Pirard, Jean-Paul ULg et al

Patent (2000)

Process for the preparation of a catalyst including a metal of group VIII and a metal of group Ib, according to which the mixture including the alkoxide precursor of an inorganic oxide and complexes ... [more ▼]

Process for the preparation of a catalyst including a metal of group VIII and a metal of group Ib, according to which the mixture including the alkoxide precursor of an inorganic oxide and complexes including the metals of group VIII and Ib and difunctional complexing compounds including an electron-donor group and a hydrolysable group is hydrolysed in order to form a gel. Process for the conversion of chloroalkanes into alkenes containing less chlorine by means of hydrogen, using such a catalyst. [less ▲]

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See detailFractal characterization of wide pore range catalysts: Application to Pd-Ag/SiO2 xerogels
Blacher, Silvia ULg; Heinrichs, Benoît ULg; Sahouli, Bendida et al

in Journal of Colloid & Interface Science (2000), 226(1), 123-130

Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO2 catalysts dried under vacuum (150 degrees C and 12 hPa) with different concentrations of Pd-Ag, Nitrogen adsorption-desorption ... [more ▼]

Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO2 catalysts dried under vacuum (150 degrees C and 12 hPa) with different concentrations of Pd-Ag, Nitrogen adsorption-desorption, mercury porosimetry, and small-angle X-ray scattering measurements have been used. The different approaches to fractal analysis and their conditions of applicability are briefly described. Results are discussed in relation to those derived previously from classical interpretations. This analysis shows that Pd-Ag/SiO2 xerogels exhibit a very open self-similar pore structure analogous to the structure of supercritically dried aerogels and that the micropore texture can be tailored by varying the silver content. (C) 2000 Academic Press. [less ▲]

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See detailMicropore size distributions of activated carbons
Blacher, Silvia ULg; Sahouli, Bendida; Heinrichs, Benoît ULg et al

in Langmuir (2000), 16(16), 6754-6756

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See detailPalladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene II. Surface composition of alloy particles
Heinrichs, Benoît ULg; Noville, Francis ULg; Schoebrechts, Jean-Paul et al

in Journal of Catalysis (2000), 192(1), 108-118

The surface composition of alloy particles in Pd-Ag/SiO2 hydrodechlorination (HDC) sol-gel catalysts has been determined by combining three experimental techniques, carbon monoxide chemisorption, X-ray ... [more ▼]

The surface composition of alloy particles in Pd-Ag/SiO2 hydrodechlorination (HDC) sol-gel catalysts has been determined by combining three experimental techniques, carbon monoxide chemisorption, X-ray diffraction, and transmission electron microscopy, Values obtained through this method show a very marked silver enrichment of the surface, as expected: as a consequence of the important gap between palladium and silver surface energies. These values are in complete agreement with surface composition curves calculated in other studies by means of Auger electron spectroscopy and infrared spectroscopy. The influence of sample pretreatment temperature as well as the influence of carbon monoxide on surface composition are discussed. (C) 2000 Academic Press. [less ▲]

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See detailDispersed Pd-Ag alloys for selective production of olefins from chlorinated alkanes
Heinrichs, Benoît ULg; Schoebrechts, Jean-Paul; Pirard, Jean-Paul ULg

in Studies in Surface Science and Catalysis (2000), 130

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See detailTextural properties of low-density xerogels
Alié, Christelle ULg; Benhaddou, Arnaud; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2000), 270(1-3), 77-90

The extent of shrinkage during drying is controlled by the balance between the capillary pressure developed in the pore liquid and the modulus of the solid network. One first method to obtain low-density ... [more ▼]

The extent of shrinkage during drying is controlled by the balance between the capillary pressure developed in the pore liquid and the modulus of the solid network. One first method to obtain low-density xerogels consists in strengthening TEOS-based alcogels by providing new monomers to the alcogel after gelation. In the second method, low-density xerogels are produced by surface modification (silylation) of the wet gel with trimethylchlorosilane. The capillary pressure is reduced and the presence of non-reactive species on the surface makes the shrinkage reversible. A reduction of the capillary pressure can be achieved by introduction of a substituted alkoxide 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) to a TEOS-based alcogel, synthesised in a single base-catalysed step. This additive acts as a nucleation agent leading to big silica particles (similar to 20 nm) with a low EDAS/TEOS ratio (similar to 0.03). The pores between those particles are also large and the drying stress is reduced. The textural properties of those three materials are compared: bulk densities of the samples modelled on the first and third method are varying in the same range (0.25-0.35 g/cm(3)) while xerogels obtained by the surface modification process are less dense (0.1-0.15 g/cm(3)). The biggest pores are observed in the third method. (C) 2000 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailResults of the tracer tests during the El Tremedal underground coal gasification at great depth
Pirard, Jean-Paul ULg; Brasseur, Alain; Coeme, Antoinette et al

in Fuel (2000), 79(5), 471-478

During the underground coal gasification (UCG) experiments at Alcorisa, Spain, a series of helium tracer tests were carried out to follow the underground cavity growth. The volume of the cavity increases ... [more ▼]

During the underground coal gasification (UCG) experiments at Alcorisa, Spain, a series of helium tracer tests were carried out to follow the underground cavity growth. The volume of the cavity increases progressively with the cumulated quantity of oxygen injected. Models based on exchange of matter between the flowing fluid and a transverse dead zone were used. Results indicate that the gasifier behaves almost like a small number of stirred tanks in series with a high level of back mixing. (C) 2000 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailSequentially compressive and intrusive mechanisms in mercury porosimetry of carbon blacks
Pirard, René ULg; Sahouli, Bendida; Blacher, Silvia ULg et al

in Journal of Colloid & Interface Science (1999), 217(1), 216-217

The mechanism of mercury penetration in two different commercial carbon blacks is studied. We show that the volume variation measured by mercury porosimetry in these systems is due to three successive ... [more ▼]

The mechanism of mercury penetration in two different commercial carbon blacks is studied. We show that the volume variation measured by mercury porosimetry in these systems is due to three successive mechanisms, which occur as the pressure increases: (1) mercury invasion of voids between macroscopic grains, (2) compaction and elastic compression of macroscopic grains, (3) intrusion in the voids of aggregates formed by primary particles. The cumulative surface calculated by the Rootare-Prenzlow equation (S-RP) in the intrusion part and the BET surface area measured by nitrogen adsorption (S-BET) are compared. (C) 1999 Academic Press. [less ▲]

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See detailDeactivation mechanisms and regeneration of a bimetallic hydrodechlorination catalyst
Heinrichs, Benoît ULg; Noville, Francis ULg; Schoebrechts, Jean-Paul et al

in Studies in Surface Science and Catalysis (1999), 126

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. A comparison between the ... [more ▼]

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. 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 Ag sites at the surface of the active Pd-Ag particles. A regeneration treatment is proposed which allows to restore the initial properties of the fresh catalyst. [less ▲]

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