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See detailDevelopment by the sol–gel process of highly dispersed Ni–Cu/SiO2 xerogel catalysts for selective 1,2-dichloroethane hydrodechlorination into ethylene
Pirard, Sophie ULg; Mahy, Julien ULg; Pirard, Jean-Paul ULg et al

in Microporous and Mesoporous Materials (in press)

Ni–Cu/SiO2 xerogel catalysts have been synthesized by cogelation of industrial tetraethoxysilane (Dynasil) and chelates of Ni and Cu with industrial 3-(2-aminoethylamino)propyltrimethoxysilane (Dynasylan ... [more ▼]

Ni–Cu/SiO2 xerogel catalysts have been synthesized by cogelation of industrial tetraethoxysilane (Dynasil) and chelates of Ni and Cu with industrial 3-(2-aminoethylamino)propyltrimethoxysilane (Dynasylan DAMO) in industrial ethanol denatured with diethyl phthalate. Despite the use of industrial grade reagents, highly dispersed bimetallic Ni–Cu/SiO2 xerogel catalysts were obtained. These samples are composed of completely accessible Ni–Cu alloy crystallites with sizes of 1.6–3.4 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears that the bimetallic complex acts as a nucleation agent in the formation of silica particles. The combination of results obtained from the calculation of the metal ratio in catalysts, H2 chemisorption and transmission electron microscopy allowed calculating the surface composition of the nickel–copper particles in Ni–Cu/SiO2 cogelled xerogel catalysts. Values obtained indicate a very pronounced surface enrichment with copper. While 1,2-dichloroethane hydrodechlorination over pure nickel mainly produces ethane, increasing copper content in bimetallic catalysts results in an increase in ethylene selectivity. The specific consumption rate of 1,2-dichloroethane decreases when copper loading increases. The turnover frequency, that is, the number of catalytic cycle per active site (nickel atom and its surrounding copper atoms) and per second, seems to be independent of surface composition of alloy particles. [less ▲]

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See detailHighly dispersed iron xerogel catalysts for p-nitrophenol degradation by photo-Fenton effects
Mahy, Julien ULg; Tasseroul, Ludivine ULg; Zubiaur, Anthony ULg et al

in Microporous and Mesoporous Materials (2014), 197

Several iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ... [more ▼]

Several iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ions. The EDAS/TEOS ratio strongly influences the texture of xerogel catalysts. The specific surface area and the micro- and mesoporous volume increase with this ratio. It seems that EDAS plays a nucleating agent role for silica particles and allows to anchor Fe-based moieties inside the silica network. Iron oxide nanoparticles of diameter 1-1.5 nm and Fe3+ ions result, encapsulated in silica particles with sizes of about 10-30 nm in diameter. The iron species was determined by Mössbauer spectroscopy and magnetometry measurements and only Fe3+ species were observed in xerogel catalysts. The Fenton and photo-Fenton effect of these catalysts were evaluated on the degradation of p-nitrophenol in aqueous media under different conditions. Results show that in the presence of H2O2, iron xerogel catalysts present a photo-Fenton effect, reaching 99 % of degradation after 24 h. [less ▲]

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See detailSynthesis, Surface characterization and photocatalytic activity of TiO2 supported on almond shell activated carbon
Omri, Abdessalem; Lambert, Stéphanie ULg; Geens, Jérémy ULg et al

in Journal of Materials Science & Technology (2014), 30(9), 894-902

Three types of photocatalysts were synthesized by metal organic chemical vapor deposition and impregnation methods using the almond shell activated carbon as support. These photocatalysts denoted by (TiO2 ... [more ▼]

Three types of photocatalysts were synthesized by metal organic chemical vapor deposition and impregnation methods using the almond shell activated carbon as support. These photocatalysts denoted by (TiO2/ASAC (V), TiO2/ASAC (I1) and TiO2/ASAC (I2)) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and nitrogen adsorptionedesorption isotherms. SEM observation shows that TiO2 was deposited on activated carbon surface. XRD results confirm that TiO2 existed in a mixture of anatase and rutile phases. The DRS spectra show the characteristic absorption edge of TiO2 at approximate 380 nm corresponding to the optical band gap of 3.26 eV. Besides, FTIR spectrum indicated the presence of (TieO) groups. The specific surface area of photocatalysts decreased drastically in comparison with the original activated carbon. The catalysts were very efficient for the photodegradation of total organic carbon (TOC) from industrial phosphoric acid solution under UV irradiation. The kinetics of photocatalytic TOC degradation was found to follow a pseudofirst- order model. The prepared TiO2/ASAC showed high photoactivity for the photodegradation of TOC in the following order: TiO2/ASAC (V) > TiO2/ASAC (I1) > TiO2/ASAC (I2) > ASAC > TiO2 (P25). [less ▲]

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See detailSynthesis of Pt/Carbon Xerogel Electrocatalysts for PEM Fuel Cells by the Multiple SEA Method
Zubiaur, Anthony ULg; Chatenet, Marian; Maillard, Frédéric et al

Poster (2014, July)

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See detailHighly dispersed iron xerogel catalysts for p-nitrophenol degradation by photo-Fenton effects
Mahy, Julien ULg; Tasseroul, Ludivine ULg; Zubiaur, Anthony ULg et al

Poster (2014, July)

Since the beginning of the industrial era, the various human activities have increased steadily, leading to a rapid technological development and a high population growth. Thus, the expansion of the ... [more ▼]

Since the beginning of the industrial era, the various human activities have increased steadily, leading to a rapid technological development and a high population growth. Thus, the expansion of the industry has heavily polluted the atmosphere, soil and water with negative consequences for humans and environment [1]. To decrease this pollution, it exists various treatment methods: chemical, physical and biological [2,3]. Among all these methods, a recent way of treatment is the degradation of pollutants in soils or waters by Fenton and photo-Fenton reactions [3] which use H2O2, iron-based compounds and UV light. In this way, several Fe2O3/SiO2 xerogel catalysts were synthesized by cogelation method by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ions [4]. Five samples were synthesized: four samples with different percentage of iron (0.5, 1, 1.5 and 2.5 theoretical wt% confirmed by ICP-AES measurements), and a sample of pure silica. TEM pictures, nitrogen adsorption-desorption and mercury porosimetry measurements have established that EDAS plays a role of nucleating agent of silica particles [5,6] and allows to anchor iron particles inside silica network [4]. Indeed, it results iron nanoparticles of diameter 1-1.5 nm encapsulated in silica particles with sizes of about 10-30 nm in diameter. The species of iron was determined by Mössbauer spectroscopy and only Fe3+ ions were observed in xerogel catalysts. Then, the Fenton and photo-Fenton effect of these catalysts were evaluated on the degradation of p-nitrophenol (PNP) in aqueous medium in different conditions. Results show that Fe2O3/SiO2 xerogels present a photo-Fenton effect with H2O2, reaching with a sample 99 % of degradation after 24 h. [1] M. A. Khan, A. M. Ghouri, Environmental pollution: its effects on life and its remedies, Journal of Arts, Science & Commerce (Vol. 2), 2011, pg 276-285. [2] M. S. Kuyukina , I. B. Ivshina, Biology of rhodococcus: chapter 9, Springer, 2010, pg 232-256. [3] J. J. Pignatello, E. Oliveros, A. MacKay, Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry, Critical Reviews in Environmental Science and Technology (Vol. 36), 2006, pg 1-84. [4] B. Heinrichs, L. Rebbouh, J.W. Geus, S. Lambert, H.C.L. Abbenhuis, F. Grandjean, G.J. Long, J.-P. Pirard, R.A. van Santen, Iron (III) species dispersed in porous silica through sol-gel chemistry, Journal of Non-Crystalline Solids (Vol. 354), 2008, pg 665-672. [5] S. Lambert, C. Alié, J.-P. Pirard, B. Heinrichs, Study of textural properties and nucleation phenomenon in Pd/SiO2 , Ag/SiO2 and Cu/SiO2 cogelled xerogel catalysts, Journal of Non-Crystalline Solids (Vol. 342), 2004, pg 70-81. [6] B. Heinrichs, S. Lambert , N. Job , J.-P. Pirard, in "Catalyst Preparation: Science and Engineering, J. R. Regalbuto (Ed.)", CRC Press, Taylor & Francis Group, Boca Raton, 2007, p. 163-208. [less ▲]

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See detailDesign of Pt/carbon xerogel catalysts for PEM fuel cells
Job, Nathalie ULg; Lambert, Stéphanie ULg; Zubiaur, Anthony ULg et al

Conference (2014, July)

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See detailUsing the Multiple SEA Method to Synthesize Pt/Carbon Xerogel Electrocatalysts for PEMFC Applications
Zubiaur, Anthony ULg; Chatenet, Marian; Maillard, Frédéric et al

in Fuel Cells - From Fundamentals to Systems (2014), 14(3), 343-349

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See detailNanostructured catalysts by sol-gel process
Lambert, Stéphanie ULg; Heinrichs, Benoît ULg

Conference (2014, April 25)

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See detailPreparation of polyaniline-modified local clay and study of its sorption capacity
Benhebal, Hadj; Chaid, Messaoud; Léonard, Angélique ULg et al

in Journal of Nanostructure in Chemistry (2014), 4(98), 6

Clay minerals are frequently used in adsorption processes with aqueous solution; it was found that the adsorption properties of clays change when the samples are modified. In this context, polyaniline ... [more ▼]

Clay minerals are frequently used in adsorption processes with aqueous solution; it was found that the adsorption properties of clays change when the samples are modified. In this context, polyaniline-modified clay nanocomposite (at 10 %) was prepared by in situ polymerization processes. The structural and morphological characteristics of the synthesized material are systematically examined by X-ray diffraction, scanning electron microscopy, thermo-gravimetry, differential scanning calorimetry and infrared spectroscopy techniques. The adsorption property of the modified clay was evaluated for the removal of a reactive dye (methylene blue) from aqueous solution at room temperature (25 C) via batch adsorption. [less ▲]

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See detailEffect of encapsulated nanoparticles on thermophillic anaerobic digestion
Al-Ahmad, Alaa Eddin ULg; Hiligsmann, Serge ULg; Lambert, Stéphanie ULg et al

Poster (2014, February 07)

Recently, enormous interest has been focused on biological applications of metal nanoparticles NPs due to their small size, high specified surface and their great potential in application to many science ... [more ▼]

Recently, enormous interest has been focused on biological applications of metal nanoparticles NPs due to their small size, high specified surface and their great potential in application to many science fields. The most studied process concerns zero valent palladium and iron NPs improving anaerobic biodegradation of chlorinated hydrocarbons (Windt et al., 2005). Moreover, investigation carried out in our lab showed that iron NPs encapsulated in silicate matrix may enhance hydrogen production by Clostridium butyricum (Beckers et al., 2013). Nevertheless the influences of metal NPs on methane producing anaerobic digestion have seldom been investigated. The present work investigates the enhancement effect of seven different metal NPs on methane production during the thermophilic anaerobic digestion. NPs of Cu, Pd, Pt, Ni, Co, Ag and Fe encapsulated in porous silica (SiO2) to prevent their coagulation and agglomeration, were added at concentration of 10-5mol/L in batch test (125ml serum bottles containing 70mL culture medium with 5g/L acetate monohydrate as the sole carbon substrate). Nickel, cobalt and iron NPs improved methane production from acetate. To confirm the previous results, the NPs were tested at different concentrations (10-4, 10-5, and 10-6 mol/L) with starch and glucose substrates. The results show that the impact increases with the increase of NPs concentrations up to 10-4 mol/L. The modified Gompertz equation was applied to describe the effect of NPs on anaerobic digestion. According to this model, the kinetic of methane production was particularly affected by nanoparticles addition. The values of the maximum methane production rate MPR (ml/day) was significantly higher 72.5% with nickel NPs at a concentration of 10-4 mol/L than the control without NPs. [less ▲]

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See detailDevelopment of alumina xerogel catalysts for biogas cleaning
Claude, Vincent ULg; Heinrichs, Benoît ULg; Toye, Dominique ULg et al

Poster (2014)

This poster resume the synthesis and characterizations of Ni/y-Al2O3 catalysts for the reforming of tars during the bio-syngas purification. The effect of an additionnal organosilane (EDAS) and a ... [more ▼]

This poster resume the synthesis and characterizations of Ni/y-Al2O3 catalysts for the reforming of tars during the bio-syngas purification. The effect of an additionnal organosilane (EDAS) and a surfactant (stearic acid) on the size,the dispersion and the sinterability of the nickel nanoparticles have been investigated. [less ▲]

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See detailAltered Desferrioxamine-mediated Iron Utilization is a Common Trait of bald Mutants of Streptomyces coelicolor
Lambert, Stéphanie ULg; Traxler, M. F.; Craig, M. et al

in Metallomics (2014)

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See detailPhotocatalytic degradation of water pollutants with visible light-sensitized TiO2 xerogels
Tasseroul, Ludivine ULg; Pirard, Sophie ULg; Lambert, Stéphanie ULg et al

in Récents Progrès en Génie des Procédés (2014), 106

To extend its photocatalytic activity to visible light, TiO2 has been doped in situ through the cogelation sol-gel proces with two dyes : free metal tetra(4-carboxyphenyl)porphyrin and nickel tetra(4 ... [more ▼]

To extend its photocatalytic activity to visible light, TiO2 has been doped in situ through the cogelation sol-gel proces with two dyes : free metal tetra(4-carboxyphenyl)porphyrin and nickel tetra(4-carboxyphenyl)porphyrin. DR and FT-IR spectroscopies have been performed to determine the interaction between porphyrins and TiO2. Cristallinity and specific surface area have been measured by XRD and N2 adsorption. The photoactivity of the doped TiO2 xerogels has been evaluated for p-nitrophenol (a model water pollutant) degradation under visible light and a kinetic study has been performed. The samples allow the degradation of 40% of p-nitrophenol in 6 h which makes them very promising for water decontamination under natural light. A kinetic study of p-nitrophenol degradation with the Ni-doped catalyst has shown that the best kinetic model involves one type of active site corresponding to the hole h+ of electron-hole pairs created at the TiO2 surface by light. The rate determining step consists of the surface reaction between adsorbed p-nitrophenol and adsorbed OH• radicals. [less ▲]

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See detailVisible-light photo-activity of alkali metal doped ZnO
Benhebal, Hadj; Chaib, Messaoud; Malengreaux, Charline ULg et al

in Journal of the Taiwan Institute of Chemical Engineers (2014), 45(1), 249-253

In order to utilize visible light more efficiently in the field of photocatalysis, Li, Na and K-doped ZnO nanoparticles were prepared using a sol–gel method. The obtained samples were characterized by BET ... [more ▼]

In order to utilize visible light more efficiently in the field of photocatalysis, Li, Na and K-doped ZnO nanoparticles were prepared using a sol–gel method. The obtained samples were characterized by BET surface area measurements, X-ray diffraction, scanning electron microscopy and UV–vis analysis. The photocatalytic activity of the photocatalysts was evaluated for the degradation of p-nitrophenol (p-NP) under visible light irradiation. It has been observed that these photocatalysts could be a promising photocatalyst for degradation of organic molecules as compared to transition metal doped ZnO under visible light. Li-doped ZnO is the most active photocatalyst and shows high photocatalytic activity for the degradation of p-nitrophenol (p-NP). The enhanced photocatalytic activity of Li-doped ZnO is mainly due to the electron trapping by lithium metal ions, small particle size, large surface area, and high surface roughness of the photocatalysts. [less ▲]

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See detailHighly dispersed Pt/C catalysts prepared by the Charge Enhanced DryImpregnation method
Cao Chongjiang; Yang Guang; Dubau Laetitia et al

in Applied Catalysis B : Environmental (2014), 150-151

tAn efficient method to synthesize highly dispersed Pt/carbon xerogel catalysts for Proton ExchangeMembrane fuel cell applications is described. The synthesis proceeds via the Charge Enhanced ... [more ▼]

tAn efficient method to synthesize highly dispersed Pt/carbon xerogel catalysts for Proton ExchangeMembrane fuel cell applications is described. The synthesis proceeds via the Charge Enhanced DryImpregnation method (CEDI), which combines dry impregnation with the Strong Electrostatic Adsorp-tion technique (SEA). The samples prepared via CEDI or SEA techniques were dried and reduced underhydrogen to obtain supported Pt nanoparticles. In order to increase the Pt mass fraction up to 10 wt.%,two successive impregnation-drying-reduction cycles were performed. The synthesized Pt nanoparticlesare homogeneously distributed on the carbon support and highly dispersed (mean Pt nanoparticle sizeof ca. 2 nm). The CEDI method is ideally suited to avoid Pt losses during the catalyst preparation. [less ▲]

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See detailEnhancement of thermophillic anaerobic digestion of methane by metal nanoparticles encapsulated in porous silica
Al-Ahmad, Alaa Eddin ULg; Hiligsmann, Serge ULg; Lambert, Stéphanie ULg et al

Poster (2013, December 05)

Increased demand and progressive depletion of fossil fuels, and worldwide concerns about greenhouse gas emissions have resulted in the development of promising technologies for renewable energy production ... [more ▼]

Increased demand and progressive depletion of fossil fuels, and worldwide concerns about greenhouse gas emissions have resulted in the development of promising technologies for renewable energy production. Therefore, potential alternatives for energy generation are intensively studied. One option is the use of biomass feedstock for the production of biogas through anaerobic digestion. This process is a biochemical technological process for the treatment of a wide range of feedstocks (e.g. organic fraction of municipal waste, animal manure and slurry, agricultural crops, etc.) to produce methane-rich biogas which can be used in replacement of fossil fuels in both heat and power generation and as a vehicle fuel. However, there are critical issues, which need to be addressed to make the production of bio-methane techno-economically viable and ecologically acceptable. One of the most important issues is the effect of trace metals addition on anaerobic digestion. These metals can be stimulatory, inhibitory, or even toxic for biochemical reactions, depending on their concentrations. As reported in literature, Ni, Co and Fe are all involved in the methane production biochemical process and serve as cofactors in enzymes which are involved in the biochemistry of methane formation (Zandvoort et al., 2006). Recently, enormous interest has been focused on biological applications of metal nanoparticles NPs due to their small size, high specified surface and their great potential in application to many science fields. The most studied process concerns zero valent palladium and iron NPs improving anaerobic biodegradation of chlorinated hydrocarbons (Windt et al., 2005). Moreover, investigation carried out in our lab showed that iron NPs encapsulated in silicate matrix may enhance hydrogen production by Clostridium butyricum (Beckers et al., 2013). Nevertheless the influences of metal NPs on methane producing anaerobic digestion have seldom been investigated. The present work investigates the enhancement effect of seven different metal NPs on methane production during the thermophilic anaerobic digestion. NPs of Cu, Pd, Pt, Ni, Co, Ag and Fe encapsulated in porous silica (SiO2) to prevent their coagulation and agglomeration, were added at concentration of 10-5mol/L in batch test (125ml serum bottles containing 70mL culture medium with 5g/L acetate monohydrate as the sole carbon substrate. Nickel, cobalt and iron NPs improved methane production from acetate. To confirm the previous results, the NPs were tested at different concentrations (10-4, 10-5, and 10-6 mol/L) with starch and glucose substrates. The results show that the impact increases with the increase of NPs concentrations up to 10-4 mol/L. The modified Gompertz equation was applied to describe the effect of NPs on anaerobic digestion. According to this model, the kinetic of methane production was particularly affected by nanoparticles addition. The values of the maximum methane production rate MPR (ml/day) was significantly higher 72.5% with nickel NPs at a concentration of 10-4 mol/L than the control without NPs. [less ▲]

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See detailEpuration catalytique de biogaz
Claude, Vincent ULg; Lambert, Stéphanie ULg; Heinrichs, Benoît ULg et al

Poster (2013, November 15)

The poster presents the recent observations concerning the of Ni-Al2O3 catalysts synthesized in 2013. Particles size, surface areas and crystallinity of the samples are controlled thanks to the initial ... [more ▼]

The poster presents the recent observations concerning the of Ni-Al2O3 catalysts synthesized in 2013. Particles size, surface areas and crystallinity of the samples are controlled thanks to the initial reactives (surfactants, EDAS). [less ▲]

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See detailSynthesis of Pt/Carbon Xerogel Electrocatalysts for PEM Fuel Cells by the Multiple SEA Method
Zubiaur, Anthony ULg; Chatenet, Marian; Maillard, Frédéric et al

Poster (2013, November 15)

1. Introduction Proton exchange membrane fuel cell (PEMFC) catalysts are generally made of carbon black-supported Pt-based nanoparticles. However, carbon blacks do not display optimal properties for ... [more ▼]

1. Introduction Proton exchange membrane fuel cell (PEMFC) catalysts are generally made of carbon black-supported Pt-based nanoparticles. However, carbon blacks do not display optimal properties for electrocatalysis: they may contain high amount of chemical impurities, are essentially microporous, and the final structure of the electrodes is hardly tunable, which may cause diffusional limitations within the catalytic layer [1]. A possible solution to these drawbacks is the use of synthetic nanostructured materials with a controllable and reproducible texture and with a pure, known and constant chemical composition; carbon xerogels (CX) exhibit such properties [2]. In addition, high Pt weight percentages are necessary to achieve high electrical performance with thin electrodes. Highly dispersed CX-supported Pt nanoparticles catalysts (Pt/CX) can be prepared by the strong electrostatic adsorption (SEA) method [3,4]. This method consists in impregnating the CX support by a solution of metal precursor at an optimum pH measured beforehand (2.4-2.5 for the impregnation of CX with H2PtCl6 [5]). If the conditions of synthesis are well controlled, the coulombic interactions between the support and the metal precursor are maximized. Metal nanoparticles are obtained after filtration, drying and reduction under hydrogen. However, achieving high Pt weight percentages requires multiple “impregnation-drying-reduction” cycles [4]. The use of large volumes of fresh 1 gPt L-1 solution for each impregnation step induces inacceptable Pt losses. In order to improve the synthesis efficiency, efforts were targeted so as to re-use the same, highly loaded Pt solution for several impregnation steps. The present study is focused on the synthesis and the characterization of Pt/CX nanoparticles by the “multiple SEA method” in view of testing and using them as PEMFC electrocatalysts. 2. Experimental The support used in this work was a CX prepared by drying and pyrolysis of a resorcinol-formaldehyde aqueous gel [6]. The pore size distribution of this CX was centred at 80 nm. After pyrolysis, the CX was crushed and sieved between 75 and 250 μm. To synthesize Pt/CX catalysts, 1 g of CX powder was first mixed with 567 mL of an H2PtCl6 solution at 8.97 mmol L-1 (i.e. 1.75 gPt L-1) with an initial pH of 2.5. The surface loading (SL), i.e. the total area of CX surface in solution, was equal to 1000 m² L-1 and the concentration of H2PtCl6 was chosen high enough to re-use the solution five times. After 1 h of stirring, the mixture was filtered and the filtrate was kept for re-use in another impregnation step. The solid was dried in an oven at 333 K during 12 h. Then, the dried material was reduced at 473 K under H2 flow (0.04 mmol s-1) during 1 h to obtain carbon-supported Pt nanoparticles. In order to synthesize several catalysts with various Pt weight percentages, the complete procedure was repeated one to five times on the same support. After the last impregnation, each catalyst was reduced at 723 K under H2 (0.04 mmol s-1) during 5 h to clean the surface of the Pt particles from chlorine residues [4]. The five catalysts are labelled according to the number of “impregnation-drying-reduction” cycles (e.g. Pt-2 for the catalyst obtained after two cycles). The Pt weight percentage of the catalysts was measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The Pt particles were observed by transmission electron microscopy (TEM) and analysed by X-ray diffraction (XRD). The electro-active surface area of the Pt nanoparticles was measured by CO stripping voltammetry performed in 1 M sulphuric acid aqueous solution [7-9]. The specific activity of Pt particles for the Oxygen Reduction Reaction (ORR) was measured on a rotating disk electrode (RDE) in the same liquid electrolyte. 3. Results and discussion Table 1 summarizes some characteristics of the synthesized catalysts. The multiple SEA method leads to the synthesis of well dispersed Pt/CX catalysts with high Pt weight percentage, PtICP, which can be adjusted via the number of “impregnation-drying-reduction” cycles, and reaches 25 wt.% after five cycles. It is worth noting that the quantity of Pt deposited on the CX in one cycle, mPt, decreases after the first two cycles. This might be due to the successive impregnations in the acidic solution, the pH of which equals 2.4 - 2.5, and to the successive reduction steps: both procedures probably modify the surface chemistry of the CX, and leads to a shift of the optimal adsorption pH. This pH shift would induce a decrease in the amount of Pt deposited during the next cycles. This hypothesis remains under investigation. The analysis of TEM micrographs indicates that the five catalysts display the same mean Pt particle size, dTEM. This is corroborated by the comparison between the surface-averaged mean particle size, dS, and the CO equivalent diameter, dCO, or between the volume-averaged mean particle size, dV, and the average crystallite size calculated from XRD, dXRD. The values of the electroactive specific surface area of the Pt particles calculated from CO Journée scientifique GEPROC 2013 Procédés et Matériaux durables Université de Liège 15 novembre 2013 stripping, SCO, are the same for all the catalysts (ca. 95 m² gPt -1). The specific activity, SA, of the catalysts for the ORR is derived from the value of the Tafel plots and intercept. Fig. 1 shows that the Tafel plots are superimposed; as a result, the values of the specific activity at a given electrode potential are nearly identical for the five catalysts, and the Tafel slope, which is characteristic of the reaction mechanism, is almost constant as well (ca. -74 mV dec- 1). Since the specific activity depends on the average size of the Pt nanoparticles (the ORR is a structure-sensitive reaction), this result indicates that the number of impregnation sequences has no impact on the Pt nanoparticle size, and degree of agglomeration. 4. Conclusions The multiple SEA method allows obtaining well dispersed Pt/CX catalysts with high weight percentage up to 25 wt.%, and particle size close to ca. 2.5 nm. Studies are in progress to determine the maximum weight percentage that can be achieved without alteration of the metal dispersion. The multiple SEA method requires the use of less Pt than the SEA method from which it is inspired. Considering the synthesis of a 25 wt.% Pt/CX, the two methods require five “impregnation-drying-reduction” cycles but, for the SEA method, five solutions of 1gPt L-1 are used instead of only one solution of 1.75 gPt L-1, the latter being re-used in the case of multiple SEA. This difference leads to a nearly threefold decrease in the consumption of Pt. Further analyses will be performed so as to determine the optimal Pt weight percentage and the optimal thickness of the catalytic layer by modifying these two variables in a series of membrane-electrodes assemblies. [less ▲]

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