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See detailHow to correctly determine the kinetics of a photocatalytic degradation reaction?
Pirard, Sophie ULg; Malengreaux, Charline ULg; Toye, Dominique ULg et al

in Chemical Engineering Journal (2014), 249

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See detailKinetic study of 4-nitrophenol photocatalytic degradation over a Zn2+ doped TiO2 catalyst prepared through an environmentally friendly aqueous sol–gel process
Malengreaux, Charline ULg; Pirard, Sophie ULg; Bartlett, John et al

in Chemical Engineering Journal (2014), 245

A kinetic study of the photocatalytic degradation of 4-nitrophenol (4-NP) under UV–visible light (330 nm < k < 800 nm) has been performed via a rigorous chemical engineering approach over a Zn2+ doped ... [more ▼]

A kinetic study of the photocatalytic degradation of 4-nitrophenol (4-NP) under UV–visible light (330 nm < k < 800 nm) has been performed via a rigorous chemical engineering approach over a Zn2+ doped TiO2 catalyst prepared through an environmentally friendly aqueous sol–gel process. The experiments have been performed at three temperatures to enable the global activation energy to be estimated. The influence of the illumination intensity has also been considered. The possibility of internal and external diffusion limitations has been studied and the results obtained demonstrated that there is no diffusional limitation during the photocatalytic degradation of the 4-NP using the selected catalyst. Therefore, the apparent specific reaction rate measured corresponds to the actual reaction rate of the chemical reaction. Parameter adjustments show that the kinetic model that provides the best fit to the experimental data corresponds to a first order reaction. A sequence of elementary steps has been considered and a pseudo-steady state approach based upon the stationary state hypothesis for reaction intermediates has been applied to obtain a kinetic rate expression in agreement with the experimental data. The mean values of the reaction rate constant found at 283 K, 288 K and 293 K are respectively equal to k1 = 0.094 ± 0.003 m3 h- 1 kgcatalyst- 1; k2 = 0.119 ± 0.004 m3 h- 1 kgcatalyst- 1 and k3 = 0.150 ± 0.023 m3 h- 1 kg catalyst-1 and the global activation energy of the degradation reaction was evaluated as 40 kJ mol-1. A phenomenological kinetic mechanism is proposed to describe the reaction at a molecular scale. Finally, statistical validations and residuals analysis have been performed to confirm that the first order model is suitable to represent the 4-NP photocatalytic degradation over time. Such studies are essential to design a reactor for water pollutant degradation on an industrial scale. [less ▲]

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See detailKinetic study of p-nitrophenol photodegradation with modified TiO2 xerogels
Tasseroul, Ludivine ULg; Pirard, Sophie ULg; Lambert, Stéphanie ULg et al

in Chemical Engineering Journal (2012), 191

TiO2 xerogels were sensitized in one step by the in situ introduction of nickel (II) tetra(4-carboxyphenyl)porphyrin (TCPPNi) into the TiO2 matrix during sol–gel synthesis. Crystalline photoactive phase ... [more ▼]

TiO2 xerogels were sensitized in one step by the in situ introduction of nickel (II) tetra(4-carboxyphenyl)porphyrin (TCPPNi) into the TiO2 matrix during sol–gel synthesis. Crystalline photoactive phase TiO2-anatase was obtained without high thermal treatments and was determined by X-ray diffraction. The presence of TCPPNi in TiO2 xerogels was established by DR-UV/Vis and FT-IR spectroscopy. The introduction of porphyrin led to a diminution of the specific surface area of TiO2 xerogels, and this diminution was analyzed by nitrogen adsorption–desorption. The particle size was estimated by SEM. The xerogel surface charge state, which influences the interactions between pollutant and TiO2, was determined by measurement of the point of zero charge. The photoactivity of xerogels was evaluated for p-nitrophenol degradation in aqueous medium at 20 ◦C. Results showed that porphyrin doped TiO2 degraded more than 40% of the p-nitrophenol whereas non doped TiO2 xerogel degraded only 10% of the compound. Moreover, porphyrin was found to improve the photoactivity of TiO2 xerogels in a similar way to UV-A pretreatment. A kinetic study of p-nitrophenol degradation was then performed. Results showed that one type of active site corresponding to the hole of electron–hole pairs was created at the TiO2 surface by light and that the rate determining step was the reaction between the adsorbed p-nitrophenol molecule and the adsorbed OH• radical. The apparent activation energy was found to be equal to 12 kJ mol−1. [less ▲]

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See detailOptimized deposition of TiO2 thin films produced by a non-aqueous sol-gel method and quantification of their photocatalytic activity
Malengreaux, Charline ULg; Timmermans, Adrien; Pirard, Sophie ULg et al

in Chemical Engineering Journal (2012), 195-196

TiO2 thin films have been produced by a dip-coating process using a non-aqueous sol-gel method. This study investigated the influence of the operating variables such as nature of the substrate, sol ... [more ▼]

TiO2 thin films have been produced by a dip-coating process using a non-aqueous sol-gel method. This study investigated the influence of the operating variables such as nature of the substrate, sol concentration, withdrawing speed of the dip-coater and number of layers on the physico-chemical properties of the films using XRD, GIXRD, UV-Vis spectroscopy, profilometry, spectroscopic ellipsometry and SEM. Photocatalytic activity of the films was evaluated by following the degradation of methylene blue under artificial UV light at 25°C. The performances of the catalysts were compared through the reaction rate constants determined using an apparent first-order kinetic model adjusted on the experimental data. This study showed that the photocatalytic activity and the reaction rate constant depend on the film thickness through the synthesis and dipping variable, with an optimum thickness of 80 nm being observed. An optimized transparent film exhibiting a high adhesion, a well crystallized TiO2-anatase phase, a good photocatalytic activity and a reaction rate constant k equal to 0.126 h-1 was obtained using a simple process. The specific photocatalytic activity of this film was higher to the one measured for TiO2 powders in previous works. [less ▲]

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See detailLarge-scale synthesis of multi-walled carbon nanotubes in a continuous inclined mobile-bed rotating reactor by the catalytic chemical vapour deposition process using methane as carbon source
Douven, Sigrid ULg; Pirard, Sophie ULg; Chan, Fang-Yue et al

in Chemical Engineering Journal (2012)

Multi-walled carbon nanotubes (CNTs) were produced in a continuous inclined mobile-bed rotating reactor by the catalytic chemical vapour deposition of methane on a bimetallic Ni-Mo/MgO catalyst whose ... [more ▼]

Multi-walled carbon nanotubes (CNTs) were produced in a continuous inclined mobile-bed rotating reactor by the catalytic chemical vapour deposition of methane on a bimetallic Ni-Mo/MgO catalyst whose activity remains constant in the course of time. Measurements performed on the continuous reactor were validated to ensure that the installation worked correctly and that measurements were precise enough. The performance of the reactor was simulated using a model based on the chemical reactor engineering approach. Hypotheses of the model were verified, and a kinetic study was performed to obtain a kinetic rate expression and to determine the catalytic activity as a function of time. The purity level of produced CNTs depends on the desired properties of the product, so the operating conditions are linked to the purity level that is required. A minimal purity level corresponds to high carbon production, and a maximal purity level corresponds to high specific productivity. It was shown that operating conditions had to be fixed to reach a given specific productivity or a given carbon production, and the optimized operating conditions leading to those two opposite purity level objectives were established. [less ▲]

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See detailInfluence of carbon xerogel textural properties on the dynamic adsorption of methyl iodide
Almazán-Almazán, M. C.; López-Domingo, F. J.; Domingo-García, M. et al

in Chemical Engineering Journal (2011), 173(1), 19-28

X-ray microtomography coupled to image analysis has been used to study the influence of the adsorbent pore texture and the experimental conditions on the dynamic adsorption of methyl iodide in packed ... [more ▼]

X-ray microtomography coupled to image analysis has been used to study the influence of the adsorbent pore texture and the experimental conditions on the dynamic adsorption of methyl iodide in packed filters. By applying this imaging technique the internal axial adsorption profiles for increasing exposure times to the gas stream are analysed. This experimental technique establishes a new technology to study in situ the dynamic adsorption of volatile compounds. Resorcinol-formaldehyde based carbon xerogels have been used as adsorbents, as their pore texture can be tuned by changing the synthesis conditions. The textural characteristics of the adsorbents (surface areas and pore volumes) have been assessed by using nitrogen and carbon dioxide adsorption as well as mercury porosimetry. The methyl iodide dynamic adsorption results show that, for the same gas flow rate and CH3I inlet concentration, the adsorbed amount is highly dependent on large pore volumes. Thus, samples with almost the same micropore volumes (adsorption volumes) have different methyl iodide adsorption capacities, which are related to, the above mentioned, large pores. The influence of both the gas carrier flow rate and the methyl iodide inlet concentration on the adsorption can be explained using the so-called linear driving force model. This approach takes into account the fact that internal transport limitations are directly related to the pore texture. Moreover, the simulation of the dynamic adsorption process has allowed relating the simulated axial concentration profiles to the experimental X-ray microtomography data. [less ▲]

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See detailExperimental procedure and statistical data treatment for the kinetic study of selective hydrodechlorination of 1,2-dichloroethane into ethylene over a Pd-Ag sol–gel catalyst
Pirard, Sophie ULg; Pirard, Jean-Paul ULg; Heyen, Georges ULg et al

in Chemical Engineering Journal (2011), 173(3), 801-812

The kinetics of selective hydrodechlorination of 1,2-dichloroethane into ethylene over a Pd- Ag/SiO2 catalyst was studied using an a priori experimental design with five independent variables—temperature ... [more ▼]

The kinetics of selective hydrodechlorination of 1,2-dichloroethane into ethylene over a Pd- Ag/SiO2 catalyst was studied using an a priori experimental design with five independent variables—temperature and partial pressures of 1,2-dichloroethane, hydrogen, ethylene and hydrogen chloride. A Langmuir–Hinshelwood model including two types of active site and the 1,2-dichloroethane adsorption as the rate-determining step was found to fit correctly with experimental data, according to the analysis of variance and the analysis of pondered residuals. The study allowed for catalytic deactivation. The rigorous experimental and statistical approach followed to carry out such a kinetic study is explained in detail. [less ▲]

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See detailMotion of carbon nanotubes in a rotating drum: The dynamic angle of repose and a bed behavior diagram
Pirard, Sophie ULg; Lumay, Geoffroy ULg; Vandewalle, Nicolas ULg et al

in Chemical Engineering Journal (2009), 146(1), 143-147

The granular flow behavior of carbon nanotubes produced by the CCVD method in a laboratory continuous inclined rotary reactor and of a catalyst was experimentally studied using a rotating drum. The ... [more ▼]

The granular flow behavior of carbon nanotubes produced by the CCVD method in a laboratory continuous inclined rotary reactor and of a catalyst was experimentally studied using a rotating drum. The dynamic angle of repose of the bulk solid and the standard variation of the solid bed surface were determined as a function of rotational speed of the rotating drum and for several filling percentages of the drum. Whatever the carbon nanotube production conditions, the dynamic angle of repose and the standard variation of the solid bed depended only on the filling percentage of the drum. Results were very interesting for practical application to carbon nanotube production in an industrial continuous inclined rotary reactor, because the granular flow behavior was the same during the reaction throughout the length of the reactor and depended only on the reactor filling. A bed behavior diagram based on the drum rotational speed and on the drum filling percentage was also constructed experimentally. The flow behavior of the solid during carbon nanotube production was on the boundary between the slumping and the rolling modes, leading to a good mixing of gas and solid during the reaction and to an improvement of the mass and heat transfer in the bed. (c) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailOptimization of experimental procedure and statistical data treatment for kinetics of ethylene hydrogenation on a copper-magnesia catalyst
Pirard, Sophie ULg; Heinrichs, Benoît ULg; Heyen, Georges ULg et al

in Chemical Engineering Journal (2008), 138(1-3), 367-378

This study is an example of practical application of kinetic data treatment for simultaneous model discrimination and parameter estimation. The study is applied to the hydrogenation of ethylene on a ... [more ▼]

This study is an example of practical application of kinetic data treatment for simultaneous model discrimination and parameter estimation. The study is applied to the hydrogenation of ethylene on a copper-magnesia catalyst and brings a deepened analysis about the experimental strategy by comparing several alternative strategies using a priori and sequential experimental designs. The best model corresponds to a Langmuir-Hinshelwood mechanism with non-competing adsorption of hydrogen and ethylene and where the rate-determining step is either the addition of molecularly adsorbed hydrogen or the addition of the second atom of hydrogen adsorbed dissociatively. Furthermore, the important question of knowing in practice how many designs and how many measurements per design are actually necessary to determine accurate kinetic and physico-chemical parameters, is addressed. A data correction procedure is also presented that takes catalyst deactivation into account. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailPd-Ag/SiO2 xerogel catalyst forming by impregnation on alumina foams
Alié, Christelle ULg; Ferauche, Fabrice; Léonard, Angélique ULg et al

in Chemical Engineering Journal (2006), 117(1), 13-22

A Pd-Ag/SiO2 xerogel catalyst prepared in one step by sol-gel process has been entrapped in cylindrical porous alumina foams of three different pore sizes in order to shape the catalyst under the ... [more ▼]

A Pd-Ag/SiO2 xerogel catalyst prepared in one step by sol-gel process has been entrapped in cylindrical porous alumina foams of three different pore sizes in order to shape the catalyst under the appropriate form with suitable mechanical resistance to be used in an industrial fixed bed reactor. After drying, calcination and reduction, the Pd-Ag/SiO2 xerogel catalyst pellets are immobilized inside the open porosity of the alumina foam. The localization of the xerogel catalyst in the alumina foams has been studied by X-ray tomography. The three-dimensional porous structure was reconstructed from the consecutive cross-sections obtained by this technique. This method shows that the Pd-Ag/SiO2 xerogel catalyst is uniformly dispersed inside the porosity of the alumina foams. Activity and selectivity of Pd-Ag/SiO2 xerogel catalyst reference or catalyst entrapped in alumina foams have been studied for selective hydrodechlorination of 1,2-dichloroethane into ethylene. The specific reaction rate obtained with catalyst entrapped in alumina foams is smaller than the one obtained from corresponding catalyst powders. The catalytic activity decrease observed for Pd-Ag/SiO2 xerogel catalyst entrapped in porous alumina foams most probably arises from diffusional limitations inside the porous texture of the alumina foams. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailAxial dispersion processes in liquid trickle flow through packed bed
Crine, Michel ULg; Asua, J. M.; L'Homme, Guy ULg

in Chemical Engineering Journal (1982), 25

Detailed reference viewed: 11 (2 ULg)