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Papers by Daniel Duprez
Studies in Surface Science and Catalysis, 2003
Abstract Supported rhodium catalysts were shown to be the most active catalysts in the ethanol st... more Abstract Supported rhodium catalysts were shown to be the most active catalysts in the ethanol steam reforming reaction. Both the metal and the support were shown to influence the final activity and selectivity of the catalyst. The influence of the preparation and reaction conditions were evaluated.
Catalysis Communications, 2002
Considering both the influence of the nature of the metal (Rh, Pt, Ni, Cu, Zn, Fe) and the role o... more Considering both the influence of the nature of the metal (Rh, Pt, Ni, Cu, Zn, Fe) and the role of the support (c-Al 2 O 3 , 12%CeO 2-Al 2 O 3 ; CeO 2 ; Ce 0:63 Zr 0:37 O 2), CO 2 is presented as a primary product in the bio-ethanol steam-reforming catalytic reaction (SRR) over some supported metal catalysts. Based on this unexpected observation, a new strategy for maximizing the hydrogen production and minimizing the CO formation is proposed. Any highly selective catalytic formulation should be free of any promoter in the water gas shift reaction (WGSR) which tends to equilibrate the SRR gas towards higher CO concentrations.
Applied Catalysis A: General, 2002
Oxygen storage capacity (OSC) measurements at 450 • C were carried out on 10 different alumina an... more Oxygen storage capacity (OSC) measurements at 450 • C were carried out on 10 different alumina and ceria-alumina supported Pd, Pt, Rh, PdRh and PtRh catalysts. Experiments were performed under both transient (0.5 and 1 Hz) and stationary reaction conditions using a mass spectrometer for the gas phase analysis every 100 ms. OSC was shown to be strongly dependent on the metal nature-oxidized or reduced. Rh appeared to be the best OSC promoter. Furthermore, ceria addition to the alumina support strongly enhances the OSC. In fact looking at the OSC values, a factor of 3 was evidenced between Pt/Al 2 O 3 and Rh/Al 2 O 3 and an additional factor of about 12 between Rh/Al 2 O 3 and Rh/CeO 2-Al 2 O 3. The metal oxides relative stability as well as the metal electronic configuration were shown to be strongly influent on the overall reactivity of the catalyst. Additional kinetic studies showed that the oxide reduction rate under CO is slower than the oxide oxidation rate under O 2. Finally a general scheme for the oxygen storage process is proposed and discussed.
Catalysts, 2015
The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literat... more The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis,
Journal of Catalysis, 2014
Applied Catalysis B: Environmental, 2014
Tungstated oxides were prepared from several supports and characterized. The tungsten surface rep... more Tungstated oxides were prepared from several supports and characterized. The tungsten surface repartition and availability depends on the initial support. The acidity in water was evaluated through a model compound reaction, cyclohexanol dehydration. The results show that acidity in water is completely different from gas phase acidity (from NH 3-TPD), evidencing the crucial role of water in the acid catalytic activity. The tungstated oxides were then mixed with Pt/ZrO 2 to obtain a bifunctional catalytic system, which was used for transforming sorbitol in water. The activity and selectivity is highly dependent on the acid phase. TiO 2-WO x led to increased activity and higher selectivity for long chain hydrocarbons (C5-C6 alkanes) which can be valorized as biofuels, when compared to traditional sorbitol transformation catalyst. Al 2 O 3-WO x is not acid in water but produces short alcohols by C C cleavage. These results provide an incentive for further catalysts preparation.
Catalysis Today, 2015
To selectively transform sorbitol into hydrocarbons in aqueous phase, new bifunctional catalytic ... more To selectively transform sorbitol into hydrocarbons in aqueous phase, new bifunctional catalytic systems are designed by associating a hydrogenating metallic catalyst (M/ZrO 2, M = Pt, Ir or Pd) and a dehydrating acidic catalyst (TiO 2-WO x) in a mechanical mixture. Zirconium oxide was chosen as support because it has virtually no dehydration activity and gives a good stability to the metal in water. This stability is evaluated through several characterizations before and after contact with the aqueous reaction medium. It is proposed that stability in water is driven by two parameters. The support stability is a key-parameter for the overall catalyst stability and the metal-support interaction determines the sintering extent. The nature of the metal has also an important influence on the activity and selectivity of the bifunctional M/ZrO 2 + TiO 2-WO x system for sorbitol transformation. Pd and Ir are slightly active and mainly transform sorbitol into isosorbide whereas Pt is selective for long-chain alkanes production. The mass ratio between metallic and acidic catalysts in the mechanical mixture also modifies the yields structure, with a Pt/ZrO 2 :TiO 2-WO x 20:80 ratio for optimal liquid hydrocarbons production.
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2013
Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 68, n°5,... more Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 68, n°5, pp. 789-946 et téléchargeable ici D o s s i e r DOSSIER Edited by/Sous la direction de : A. Daudin et A. Quignard PART 2 Second and Third Generation Biofuels: Towards Sustainability and Competitiveness Deuxième et troisième génération de biocarburants : développement durable et compétitivité
Catalysts
This review aims to give a general overview of the recent use of tungsten-based catalysts for wid... more This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Brønsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for nume...
Studies in Surface Science and Catalysis, 2006
Thin (300–1000 nm) mesoporous silica coatings with hexagonal and cubic mesostructure have been pr... more Thin (300–1000 nm) mesoporous silica coatings with hexagonal and cubic mesostructure have been prepared on Pyrex® 7740 borosilicate glass substrates by the evaporation induced self assembly assisted sol-gel route. Prior to the synthesis, a 50 nm TiO2 layer has been deposited on the substate by atomic layer deposition from titanium tetrachloride and water to reach better adhesion of coatings to the walls of the substrate. The coatings were produced by templating a silica precursor (TEOS) with an EOxPOyEOx amphiphilic triblock copolymer (EO=ethylene oxide, PO=propylene oxide, x=106, y=70) at a pH of 2. A surfactant/silica ratio of 0.0076 was found to be optimal at a spinning rate of 1500 rpm to obtain the coatings with a surface area above 500 m2/g and a monomodal pore size distribution with a mean pore size of 6.9 nm. Mixed-metal precursor clusters [Ph4P2[Ru5PtC(CO)15 have been inserted into the mesoporous support. Then, the mesoporo-encapsulated clusters were activated by gentle hea...
Catalysts
The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduc... more The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduction (SCR) catalysts with two copper loadings (2.8 wt. % and 6.1 wt. %) in order to compare samples with or without over-exchanged copper. Na was added by wet-impregnation using two solvents: water or ethanol. Catalysts were evaluated in Standard and Fast-SCR conditions, as well as in NO and NH 3 oxidation. They were characterized by H 2-TPR, NO and NH 3 adsorption monitored by FT-IR. As expected, whatever the copper loading, ammonia adsorption capacity was decreased by Na additions. Interestingly, characterizations also showed that Na impregnation in water favors the migration of the Cu-exchanged species, leading to the formation of CuO extra-framework compounds. Consequently, for both copper loadings, Na impregnation in water led to a stronger catalyst deactivation than impregnation in ethanol. Finally, the NO x conversion at low temperature (250 • C) appeared mainly affected by the loss in NH 3 adsorption capacity whereas the deNO x deactivation at high temperature (500 • C) was rather governed by the decrease in the exchanged copper ratio, which also induced a partial inhibition of NO and NH 3 oxidation behaviors.
Applied Catalysis
The effect of sulphur on the coking of Rh/A1203 in the steam reforming of 1-methylnaphthalene was... more The effect of sulphur on the coking of Rh/A1203 in the steam reforming of 1-methylnaphthalene was studied at 440-5OO"C, 1 atm and a steam-to-1-methylnaphthalene molar ratio of 14. Three grades of 1-methylnaphthalene were used, containing 690,80 and < 5 ppm of sulphur. In all instances the presence of sulphur compounds considerably increased the coking rate. The profiles of coke and of sulphur in the catalyst bed and inside the pellets were very similar, which explains why powder catalysts were deactivated much faster than pellet catalysts. The role of sulphur has not been entirely elucidated and could be due either to rapid cracking of the sulphur compounds themselves or to inhibition by sulphur of the carbon-steam reactions. These two hypotheses are discussed in the light of other studies concerning the mutual influence of coke and sulphur in the deactivation of metal catalysts.
Journal de Chimie Physique
Journal of the American Chemical Society, Sep 1, 2009
Organized macroporous-mesoporous alumina can be obtained via a dual-templating approach. Monodisp... more Organized macroporous-mesoporous alumina can be obtained via a dual-templating approach. Monodispersed polystyrene beads promote macropore formation, while a P123 surfactant templating agent drives the formation of ordered hexagonal mesopores throughout the alumina framework. These well-defined pore networks coexist over a wide range of temperatures and macropore sizes.
Studies in Surface Science and Catalysis, Dec 31, 1993
Studies in Surface Science and Catalysis, 2003
Abstract Supported rhodium catalysts were shown to be the most active catalysts in the ethanol st... more Abstract Supported rhodium catalysts were shown to be the most active catalysts in the ethanol steam reforming reaction. Both the metal and the support were shown to influence the final activity and selectivity of the catalyst. The influence of the preparation and reaction conditions were evaluated.
Catalysis Communications, 2002
Considering both the influence of the nature of the metal (Rh, Pt, Ni, Cu, Zn, Fe) and the role o... more Considering both the influence of the nature of the metal (Rh, Pt, Ni, Cu, Zn, Fe) and the role of the support (c-Al 2 O 3 , 12%CeO 2-Al 2 O 3 ; CeO 2 ; Ce 0:63 Zr 0:37 O 2), CO 2 is presented as a primary product in the bio-ethanol steam-reforming catalytic reaction (SRR) over some supported metal catalysts. Based on this unexpected observation, a new strategy for maximizing the hydrogen production and minimizing the CO formation is proposed. Any highly selective catalytic formulation should be free of any promoter in the water gas shift reaction (WGSR) which tends to equilibrate the SRR gas towards higher CO concentrations.
Applied Catalysis A: General, 2002
Oxygen storage capacity (OSC) measurements at 450 • C were carried out on 10 different alumina an... more Oxygen storage capacity (OSC) measurements at 450 • C were carried out on 10 different alumina and ceria-alumina supported Pd, Pt, Rh, PdRh and PtRh catalysts. Experiments were performed under both transient (0.5 and 1 Hz) and stationary reaction conditions using a mass spectrometer for the gas phase analysis every 100 ms. OSC was shown to be strongly dependent on the metal nature-oxidized or reduced. Rh appeared to be the best OSC promoter. Furthermore, ceria addition to the alumina support strongly enhances the OSC. In fact looking at the OSC values, a factor of 3 was evidenced between Pt/Al 2 O 3 and Rh/Al 2 O 3 and an additional factor of about 12 between Rh/Al 2 O 3 and Rh/CeO 2-Al 2 O 3. The metal oxides relative stability as well as the metal electronic configuration were shown to be strongly influent on the overall reactivity of the catalyst. Additional kinetic studies showed that the oxide reduction rate under CO is slower than the oxide oxidation rate under O 2. Finally a general scheme for the oxygen storage process is proposed and discussed.
Catalysts, 2015
The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literat... more The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis,
Journal of Catalysis, 2014
Applied Catalysis B: Environmental, 2014
Tungstated oxides were prepared from several supports and characterized. The tungsten surface rep... more Tungstated oxides were prepared from several supports and characterized. The tungsten surface repartition and availability depends on the initial support. The acidity in water was evaluated through a model compound reaction, cyclohexanol dehydration. The results show that acidity in water is completely different from gas phase acidity (from NH 3-TPD), evidencing the crucial role of water in the acid catalytic activity. The tungstated oxides were then mixed with Pt/ZrO 2 to obtain a bifunctional catalytic system, which was used for transforming sorbitol in water. The activity and selectivity is highly dependent on the acid phase. TiO 2-WO x led to increased activity and higher selectivity for long chain hydrocarbons (C5-C6 alkanes) which can be valorized as biofuels, when compared to traditional sorbitol transformation catalyst. Al 2 O 3-WO x is not acid in water but produces short alcohols by C C cleavage. These results provide an incentive for further catalysts preparation.
Catalysis Today, 2015
To selectively transform sorbitol into hydrocarbons in aqueous phase, new bifunctional catalytic ... more To selectively transform sorbitol into hydrocarbons in aqueous phase, new bifunctional catalytic systems are designed by associating a hydrogenating metallic catalyst (M/ZrO 2, M = Pt, Ir or Pd) and a dehydrating acidic catalyst (TiO 2-WO x) in a mechanical mixture. Zirconium oxide was chosen as support because it has virtually no dehydration activity and gives a good stability to the metal in water. This stability is evaluated through several characterizations before and after contact with the aqueous reaction medium. It is proposed that stability in water is driven by two parameters. The support stability is a key-parameter for the overall catalyst stability and the metal-support interaction determines the sintering extent. The nature of the metal has also an important influence on the activity and selectivity of the bifunctional M/ZrO 2 + TiO 2-WO x system for sorbitol transformation. Pd and Ir are slightly active and mainly transform sorbitol into isosorbide whereas Pt is selective for long-chain alkanes production. The mass ratio between metallic and acidic catalysts in the mechanical mixture also modifies the yields structure, with a Pt/ZrO 2 :TiO 2-WO x 20:80 ratio for optimal liquid hydrocarbons production.
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2013
Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 68, n°5,... more Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 68, n°5, pp. 789-946 et téléchargeable ici D o s s i e r DOSSIER Edited by/Sous la direction de : A. Daudin et A. Quignard PART 2 Second and Third Generation Biofuels: Towards Sustainability and Competitiveness Deuxième et troisième génération de biocarburants : développement durable et compétitivité
Catalysts
This review aims to give a general overview of the recent use of tungsten-based catalysts for wid... more This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Brønsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for nume...
Studies in Surface Science and Catalysis, 2006
Thin (300–1000 nm) mesoporous silica coatings with hexagonal and cubic mesostructure have been pr... more Thin (300–1000 nm) mesoporous silica coatings with hexagonal and cubic mesostructure have been prepared on Pyrex® 7740 borosilicate glass substrates by the evaporation induced self assembly assisted sol-gel route. Prior to the synthesis, a 50 nm TiO2 layer has been deposited on the substate by atomic layer deposition from titanium tetrachloride and water to reach better adhesion of coatings to the walls of the substrate. The coatings were produced by templating a silica precursor (TEOS) with an EOxPOyEOx amphiphilic triblock copolymer (EO=ethylene oxide, PO=propylene oxide, x=106, y=70) at a pH of 2. A surfactant/silica ratio of 0.0076 was found to be optimal at a spinning rate of 1500 rpm to obtain the coatings with a surface area above 500 m2/g and a monomodal pore size distribution with a mean pore size of 6.9 nm. Mixed-metal precursor clusters [Ph4P2[Ru5PtC(CO)15 have been inserted into the mesoporous support. Then, the mesoporo-encapsulated clusters were activated by gentle hea...
Catalysts
The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduc... more The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduction (SCR) catalysts with two copper loadings (2.8 wt. % and 6.1 wt. %) in order to compare samples with or without over-exchanged copper. Na was added by wet-impregnation using two solvents: water or ethanol. Catalysts were evaluated in Standard and Fast-SCR conditions, as well as in NO and NH 3 oxidation. They were characterized by H 2-TPR, NO and NH 3 adsorption monitored by FT-IR. As expected, whatever the copper loading, ammonia adsorption capacity was decreased by Na additions. Interestingly, characterizations also showed that Na impregnation in water favors the migration of the Cu-exchanged species, leading to the formation of CuO extra-framework compounds. Consequently, for both copper loadings, Na impregnation in water led to a stronger catalyst deactivation than impregnation in ethanol. Finally, the NO x conversion at low temperature (250 • C) appeared mainly affected by the loss in NH 3 adsorption capacity whereas the deNO x deactivation at high temperature (500 • C) was rather governed by the decrease in the exchanged copper ratio, which also induced a partial inhibition of NO and NH 3 oxidation behaviors.
Applied Catalysis
The effect of sulphur on the coking of Rh/A1203 in the steam reforming of 1-methylnaphthalene was... more The effect of sulphur on the coking of Rh/A1203 in the steam reforming of 1-methylnaphthalene was studied at 440-5OO"C, 1 atm and a steam-to-1-methylnaphthalene molar ratio of 14. Three grades of 1-methylnaphthalene were used, containing 690,80 and < 5 ppm of sulphur. In all instances the presence of sulphur compounds considerably increased the coking rate. The profiles of coke and of sulphur in the catalyst bed and inside the pellets were very similar, which explains why powder catalysts were deactivated much faster than pellet catalysts. The role of sulphur has not been entirely elucidated and could be due either to rapid cracking of the sulphur compounds themselves or to inhibition by sulphur of the carbon-steam reactions. These two hypotheses are discussed in the light of other studies concerning the mutual influence of coke and sulphur in the deactivation of metal catalysts.
Journal de Chimie Physique
Journal of the American Chemical Society, Sep 1, 2009
Organized macroporous-mesoporous alumina can be obtained via a dual-templating approach. Monodisp... more Organized macroporous-mesoporous alumina can be obtained via a dual-templating approach. Monodispersed polystyrene beads promote macropore formation, while a P123 surfactant templating agent drives the formation of ordered hexagonal mesopores throughout the alumina framework. These well-defined pore networks coexist over a wide range of temperatures and macropore sizes.
Studies in Surface Science and Catalysis, Dec 31, 1993
Physical Chemistry Chemical Physics, 2008
Mn-based oxide supports were synthesized using different procedures: (i) carbonate co-precipitati... more Mn-based oxide supports were synthesized using different procedures: (i) carbonate co-precipitation method, leading to the formation of a hexaaluminate crystallized solid (La 0.2 Sr 0.3 Ba 0.5 MnAl 11 O 19 ) and (ii) solid-solid diffusion method, leading to the formation of a doped y-Al 2 O 3 crystallized solid (nominal composition: 60 wt% La 0.2 Sr 0.3 Ba 0.5 MnAl 11 O 19 + 40 wt% Al 2 O 3 ). Impregnation of 1.0 wt%Pd was carried out on both oxides. The solids were tested for the catalytic methane combustion up to 700 1C. It was observed that adding palladium resulted in an important increase in the catalytic activity. The combined use of H 2 -TPR and XPS techniques reveals that only Mn 3+ /Mn 2+ redox ''couple'' is present in the solids, whatever the synthesis procedure used. The fraction Mn 3+ /Mn is proportional to the total Mn content in the solid support, whatever the sample structure (hexaaluminate or doped y-Al 2 O 3 ) and its morphology (large crystals or aggregates of small particles, respectively). Pd impregnation and further calcination at 650 1C has no significant effect on the Mn 3+ /Mn fraction. However, some changes in Mn 3+ reduction profile are observed, depending on the solid structure. Indeed, palladium addition strongly affects the manganese reducibility with an important shift of the reduction process to lower temperatures (B100 1C). On the basis of redox properties observed for the different catalysts, a Mars-van-Krevelen redox mechanism, with oxygen transfer from support oxides to palladium particles, is proposed to explain the difference in terms of catalytic conversion and stability with respect to a 1.0 wt%Pd/Al 2 O 3 reference sample.