References of "Pirard, Jean-Paul"
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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 detailCharacterization of gels via solvent desorption measurements
Gommes, Cédric ULg; Noville, Francis; Pirard, Jean-Paul ULg

Poster (2007, May)

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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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See detailPhotodegradation of bacteria with TiO2 produced by sol-gel method
Tasseroul, Ludivine ULg; Pàez Martinez, Carlos ULg; Braconnier, Benoît et al

Poster (2007)

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See detailInvestigation of the preparation and activity of gold catalysts in the total oxidation of n-hexane
Cellier Caroline; Lambert, Stéphanie ULg; Gaigneaux Eric et al

in Applied Catalysis B : Environmental (2007), 70

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition–precipitation is discussed through ... [more ▼]

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition–precipitation is discussed through comparison of the samples prepared by this method and others prepared by anion adsorption method. The influence of the pH and of the origin of TiO2 support used are additionally addressed. The difference of gold dispersion observed between the two methods is attributed to a difference of mobility of the gold precursors during the thermal treatment rather than to a difference of dispersion over the uncalcined samples. The mechanism of gold deposition–precipitation actually involves the reactions of gold hydroxy-chloride species with the surface. Another part of the work, thus, concerned the use of the deposition–precipitation method to prepare a Au/MnO2 catalyst. It is shown that the activity of g-MnO2 is directly proportional to its surface area and that the deposition–precipitation procedure decreases the surface and activity of MnO2. However, the deposition of gold allows to avoid a too deep sintering of g-MnO2 and, thus, helps to somehow preserve its activity. [less ▲]

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See detailInvestigation of the preparation and activity of gold catalysts in the total oxidation of n-hexane
Cellier, Caroline; Lambert, Stéphanie ULg; Gaigneaux, Eric M. et al

in Applied Catalysis B : Environmental (2007), 70(1-4), 406-416

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition-precipitation is discussed through ... [more ▼]

The factors affecting the preparation of Au/TiO2 catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition-precipitation is discussed through comparison of the samples prepared by this method and others prepared by anion adsorption method. The influence of the pH and of the origin of TiO2 support used are additionally addressed. The difference of gold dispersion observed between the two methods is attributed to a difference of mobility of the gold precursors during the thermal treatment rather than to a difference of dispersion over the uncalcined samples. The mechanism of gold deposition-precipitation actually involves the reactions of gold hydroxy-chloride species with the surface. Another pan of the work, thus, concerned the use of the deposition-precipitation method to prepare a Au/MnO2 catalyst. It is shown that the activity of gamma-MnO2 is directly proportional to its surface area and that the deposition-precipitation procedure decreases the surface and activity of MnO2. However, the deposition of gold allows to avoid a too deep sintering of gamma-MnO2 and, thus, helps to somehow preserve its activity. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailCompressing some sol-gel materials reduces their stiffness: a textural analysis
Gommes, Cédric ULg; Job, Nathalie ULg; Blacher, Silvia ULg et al

in Studies in Surface Science and Catalysis (2007), 160

The mechanical behaviour of two series of silica and of resorcinol xerogels is analyzed by mercury porosimetry. The data are expressed as pressure-density curves, which enables textural information to be ... [more ▼]

The mechanical behaviour of two series of silica and of resorcinol xerogels is analyzed by mercury porosimetry. The data are expressed as pressure-density curves, which enables textural information to be obtained. In particular, it is shown that some of the analyzed samples exhibit a marked lowering of their mechanical stiffness upon compression. This observation is analyzed in terms of the collapse of the sample’s porosity and of the heterogeneity of the microstructure. [less ▲]

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See detailAnalysis of kinetic models of multi-walled CNT synthesis
Pirard, Sophie ULg; Douven, Sigrid ULg; Pirard, Jean-Paul ULg

in Carbon (2007), 45(15), 3050-3052

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See detailCharacterization of gels via solvent desorption measurements
Gommes, Cédric ULg; Noville, Francis ULg; Pirard, Jean-Paul ULg

in Adsorption (2007), 13(5-6), 533-540

The present paper shows how a standard volumetric adsorption device can be used to measure solvent desorption isotherms on gels. As gels are very soft materials, they shrink significantly during the ... [more ▼]

The present paper shows how a standard volumetric adsorption device can be used to measure solvent desorption isotherms on gels. As gels are very soft materials, they shrink significantly during the measurement, and the data have to be analyzed in terms of the mechanical properties of the gel's skeleton. Methanol desorption isotherms are measured on a series of silica gels, and the results are compared with independent characterizations, notably beam bending. [less ▲]

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See detailHierarchical multimodal mesoporous carbon materials with parallel macrochannels
Su, Bao-Lian; Vantomme, Aurelien; Surahy, Lidwine et al

in Chemistry of Materials (2007), 19(13), 3325-3333

Hierarchically structured multimodal meso-macroporous carbon materials have been prepared by using the nanoreplication of the mesoporous walls of a meso-macroporous zirconia exotemplate. Like the zirconia ... [more ▼]

Hierarchically structured multimodal meso-macroporous carbon materials have been prepared by using the nanoreplication of the mesoporous walls of a meso-macroporous zirconia exotemplate. Like the zirconia exotemplate, the pure carbon material possesses funnel shaped straight macrochannels, parallel to each other and perpendicular to the tangent of the particles' dense mesoporous shell. As a result of the funnel-like shape, each macrochannel has a pore size gradient with a large opening centered at 300-700 nm. The walls of the macrochannels and the dense mesoporous shells are formed by a hierarchical mesostructured porous system with uniform mesopore sizes centered at 3, 15-17, and 25-50 nm. Macrochannels are interconnected with hierarchically mesostructured walls and shells. A high surface area of 950 m(2)/g with a mesopore volume of 0.44 cm(3)/g is obtained. The possibility of the nanoreplication of other meso-macroporous oxides such as aluminosilicates, titania, and niobium oxide with different macrochannel size, shape, and organization has also been studied to generate meso-macroporous carbon materials with different organizations of the macrochannels. [less ▲]

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See detailSynthesis of transition metal-doped carbon xerogels by cogelation
Job, Nathalie ULg; Pirard, René ULg; Vertruyen, Bénédicte ULg et al

in Journal of Non-Crystalline Solids (2007), 353(24-25), 2333-2345

The cogelation process, i.e. the co-polymerization of a metal complex with the gel precursors, was used for the synthesis of transition metal-doped resorcinol-formaldehyde gels. The aim of this process is ... [more ▼]

The cogelation process, i.e. the co-polymerization of a metal complex with the gel precursors, was used for the synthesis of transition metal-doped resorcinol-formaldehyde gels. The aim of this process is to anchor the metal to the polymer so that the former does not sinter during the pyrolysis step leading to porous carbon. Cu-, Ni-, Pd- or Pt-loaded gels were prepared by this technique. After drying and pyrolysis, Pd and Pt were obtained as metal nanoparticles (2-5 nm in diameter) inserted in the carbon nodules, when the complexing agent and the synthesis conditions were well chosen. These small metal particles were inaccessible to reactive gases, probably due to carbon deposit at the metal surface during pyrolysis: CO almost did not chemisorb. Oxidation of the support or pyrolysis under reductive atmosphere was applied to the metal-doped gels and carbons in order to make the surface of the metal particles accessible, but these treatments develop the macropores only. The cogelation process is then suitable to prepare metal nanoparticles protected from the outside by encapsulation in the carbon matrix. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailSynthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 by successive freeze-drying and self-ignition of a hydroxypropylmethyl cellulose solution
Traina, Karl ULg; Steil, M. C.; Pirard, Jean-Paul ULg et al

in Journal of the European Ceramic Society (2007), 27(12), 3469-3474

The present paper reports the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing ... [more ▼]

The present paper reports the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing hydroxypropylmethyl cellulose. The precursor powder obtained after self-ignition was submitted to various thermal treatments and the resulting powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption-desorption isotherm analysis, mercury porosimetry and laser granulometry. It turns out that this synthesis method yields single-phase powders with good homogeneity and sinterability properties. The precursor powder treated at 1200 degrees C presents a coral-like structure which collapses under application of low uniaxial pressure, resulting in a narrow grain size distribution suitable for sintering (98.8% relative density for a pellet sintered at 1400 degrees C during 1 h). The fact that no milling step is necessary is an additional advantage of this method, which shows promising prospects for the synthesis of other multicationic oxides. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMultiscale image analysis of microcellular solids: application to hybrid silica xerogels
Gommes, Cédric ULg; Pirard, Jean-Paul ULg; Blacher, Silvia ULg

in Journal of Microscopy (2007), 226

A general methodology is proposed to characterize microcellular solids, the structure of which consists of a three-dimensional network of filamentary structures. The analysis is based on transmission ... [more ▼]

A general methodology is proposed to characterize microcellular solids, the structure of which consists of a three-dimensional network of filamentary structures. The analysis is based on transmission electron microscopy observation of the filaments individually and of their spatial arrangement. The micrographs are analyzed with greytone digital image analysis techniques, such as opening granulometry and correlation analysis. The methodology is applied to hybrid organic–inorganic low-density silica solids synthesized by the sol–gel method with an organically modified co-reactant. The quantitative impact of the coreactant on each structural level of the structure is assessed quantitatively. [less ▲]

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