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Joël Barrault - One of the best experts on this subject based on the ideXlab platform.
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high efficiency cosn zno catalysts for the hydrogenation of methyl oleate
Catalysis Today, 2012Co-Authors: Karine De Oliveira Vigier, Yannick Pouilloux, Joël BarraultAbstract:Abstract The hydrogenation of methyl oleate (methyl cis-9-octadecenoate) to oleyl Alcohol (methyl cis-9-octadecen-1-ol) was studied in the presence of a bimetallic CoSn supported over zinc oxide catalyst in a stainless steel batch reactor at 270 °C and 8.0 MPa of hydrogen. The active species in the reduction of methyl oleate into Unsaturated Alcohols was CoSn2. In order to increase the amount of these active species the nature of the precursor salts was studied. These results have shown that the carbonyl cobalt precursor is the optimum salt for the hydrogenation of methyl oleate into Unsaturated Alcohol since the selectivity to Unsaturated Alcohol reached 55% at 80% of conversion. Moreover, the selectivity is governed by the reduction of the heavy esters (oleyl oleate and oleyl stearate) formed, which can occur in the presence of small Co–Sn2 particles, well dispersed on the catalyst surface and with a high surface content.
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selective hydrogenation of methyl oleate into Unsaturated Alcohols relationships between catalytic properties and composition of cobalt tin catalysts
Catalysis Today, 2000Co-Authors: Yannick Pouilloux, F Autin, Joël BarraultAbstract:Abstract The selective hydrogenation of methyl oleate into oleyl Alcohol, intermediate in the formulation of surfactant agents, is carried out over bimetallic catalysts containing cobalt and tin. However the tin content modifies the rates of the hydrogenation of the esters (methyl oleate and oleyl oleate) and of the side reaction of the transesterification between the methyl oleate and the Alcohol formed. Indeed, the maximum of the Unsaturated Alcohol yield depends on the Sn/metal ratio. The analyses of the catalyst surface by XPS have shown that there are coexistence of metallic particles (Co 0 ) and/or oxides (CoO) with two different tin oxides (SnO x , SnO y ), the SnO x species being close to zerovalent metallic particles. It is suggested that (1) [Co 0 ⋯(SnO x ) 2 ] should be the active sites for the selective hydrogenation of ester, (2) the SnO y species favor the reaction of transesterification and (3) the free metallic particles favor the hydrogenation of ethylenic bonds. On the other hand, the preparation method of the catalyst and the nature of the support modify the surface composition of the solid. The use of alumina or zinc oxide lead to the same yield of Unsaturated Alcohol whereas silica which has much more metallic Co 0 species gives a low activity due to a large tin enrichment. Over CoSn catalysts reduced with NaBH 4 , owing to the formation of cobalt aluminate, a small content of metallic cobalt is observed. The preparation of CoSn catalyst via a sol–gel method improves the homogeneity and the dispersion of the active sites. But the strong interactions between cobalt and the support do not allow the formation of both metallic cobalt and mixed active centers (Co 0 , SnO x ). Furthermore, some kinetic studies obtained with cobalt catalysts show that (1) the transesterification reaction is faster than the hydrogenation of esters, (2) the presence of methanol issued from the hydrogenation and from the transesterification strongly modifies the oleyl oleate hydrogenation.
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Preparation of oleyl Alcohol from the hydrogenation of methyl oleate in the presence of cobalt-tin catalysts
Applied Catalysis A: General, 1998Co-Authors: Yannick Pouilloux, A. Piccirilli, F Autin, Claude Guimon, Joël BarraultAbstract:Abstract The hydrogenation of methyl oleate into oleyl Alcohol was studied in the presence of a CoSn catalyst at 270°C and 8.0 MPa. The selectivity of the CoSn catalyst to oleyl Alcohol is comparable to that of the RuSn catalyst but the CoSn catalyst is less active. The activity and the selectivity to Unsaturated Alcohol was maximum for an atomic Sn/Co ratio of 1. Nevertheless, the side reaction, the transesterification between methyl oleate and Alcohol, still occurs in the presence of CoSn catalysts. The method of preparation influenced the activity, impregnation and reduction with sodium borohydride dry>impregnation>sol–gel technique, but the oleyl Alcohol yields, obtained over the catalyst reduced with sodium borohydride or over the catalyst prepared by a sol–gel technique, are similar. From XPS analysis, Co0 and two tin-oxide species were identified at the surface of the CoSnB/Al2O3 catalyst after reduction with sodium borohydride. The addition of tin species does not modify the surface cobalt content. The reduction with sodium borohydride increased the reducibility of the metal oxide species.
Albert M Vannice - One of the best experts on this subject based on the ideXlab platform.
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liquid phase citral hydrogenation over sio2 supported group viii metals
Journal of Catalysis, 2001Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Abstract Liquid-phase citral hydrogenation over SiO 2 -supported Group VIII metals at 300 K and 1 atm was studied in the absence of all transport limitations as verified by the Madon–Boudart test and the Weisz–Prater criterion. The initial TOF (turnover frequency) for citral hydrogenation varied by three orders of magnitude and exhibited the following trend: Pd>Pt>Ir>Os>Ru>Rh>Ni>Co⪢Fe (no activity was detected over Fe/SiO 2 ). When TOF is correlated with percentage d-character, a volcano plot results. There are significant differences in product distribution among the different metals, with Os, Ru, and Co exhibiting high selectivity toward the Unsaturated Alcohol isomers (geraniol and nerol), while Rh, Ni, and Pd were more selective for citronellal and isopulegol. The variation in product distribution among the various metals is rationalized on the basis of the d-band widths that affect the relative importance of the stabilizing two-electron interactions and destabilizing four-electron interactions. With the exception of Ni/SiO 2 , all catalysts exhibited substantial deactivation that was attributed to inhibition by adsorbed CO produced by the decomposition of either citral or the Unsaturated Alcohol. In contrast, Ni/SiO 2 exhibited an initially low, stable TOF during the first 7 h that then increased fourfold and again remained constant to 84% citral conversion, at which point the run was terminated.
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influence of metal support interactions on the kinetics of liquid phase citral hydrogenation
Journal of Molecular Catalysis A-chemical, 2000Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Abstract The kinetics of liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) on Pt/TiO 2 catalysts were studied between 298–423 K and 7–21 atm H 2 and compared to those reported earlier for Pt/SiO 2 catalysts. The kinetic data were shown to be free of transport limitations by application of the Madon–Boudart test and the Weisz–Prater criterion. Near zero- and first-order kinetics were observed for the initial rate of citral hydrogenation over the Pt/TiO 2 -LTR ( T red =473 K ) and Pt/SiO 2 catalysts with respect to citral concentration and hydrogen pressure, respectively. In contrast, each dependency dropped by about one order with Pt/TiO 2 -HTR ( T red =773 K ) catalysts as they were negative first-order on citral concentration and near zero-order on hydrogen pressure. Furthermore, the initial rates over Pt/TiO 2 -LTR and Pt/SiO 2 exhibited an activity minimum as temperature increased whereas conventional Arrhenius behavior was exhibited by Pt/TiO 2 -HTR with an activation energy of 18 kcal/mol. Pt/TiO 2 -LTR and HTR catalysts initially exhibited 90% selectivity to the Unsaturated Alcohol as compared to 40% for hydrogenation over Pt/SiO 2 . Metal–support interactions (MSI) resulted in a dramatic enhancement in specific activity at 373 K, 20 atm H 2 and 1 M citral in hexane as Pt/TiO 2 -HTR exhibited a turnover frequency of 1.0 compared to 0.02 s −1 for Pt/TiO 2 -LTR and 0.004 s −1 for Pt/SiO 2 . The reaction kinetics with Pt/TiO 2 -HTR in the differential conversion regime were described by a conventional Langmuir–Hinshelwood model assuming quasi-equilibrium for reactant adsorption, competitive adsorption between citral and hydrogen, and addition of the first H atom as the rate determining step. The reaction rate at higher conversions was modeled by invoking a decarbonylation reaction similar to that proposed earlier for this reaction over Pt/SiO 2 catalysts to explain any observed deactivation.
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liquid phase hydrogenation of citral over pt sio2 catalysts i temperature effects on activity and selectivity
Journal of Catalysis, 2000Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) over Pt/SiO2 catalysts was studied in the temperature and pressure ranges 298–423 K and 7–21 atm, respectively. The reaction kinetics were shown to be free of artifacts arising from transport limitations and poisoning effects. The reaction rate in hexane as the solvent exhibited an activity minimum at 373 K. The initial turnover frequency for citral disappearance over 1.44% Pt/SiO2 catalyst at 20 atm H2 pressure decreased from 0.19 s−1 at 298 K to 0.02 s−1 at 373 K, but exhibited normal Arrhenius behavior between 373 and 423 K with an activation energy of 7 kcal/mol. Reaction at 298 K produced substantial deactivation, with the rate decreasing by more than an order of magnitude during the first 4 h of reaction; however, reaction at temperatures greater than 373 K exhibited negligible deactivation and a constant rate up to citral conversions greater than 70%. These unusual temperature effects were modeled using Langmuir–Hinshelwood kinetics invoking dissociative adsorption of hydrogen, competitive adsorption between hydrogen and the organic compounds, and addition of the second hydrogen atom to each reactant as the rate-determining step. Decomposition of the Unsaturated Alcohol (either geraniol or nerol) was proposed to occur concurrently with the hydrogenation steps to yield adsorbed CO and carbonaceous species which cause the deactivation, but at higher temperatures these species could be removed from the Pt surface by desorption or rapid hydrogenation, respectively. The activity minimum observed in the present study is attributed to the relative rates of the Alcohol decomposition reaction and CO desorption, with the decomposition reaction having an activation barrier lower than that for CO desorption.
Yannick Pouilloux - One of the best experts on this subject based on the ideXlab platform.
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high efficiency cosn zno catalysts for the hydrogenation of methyl oleate
Catalysis Today, 2012Co-Authors: Karine De Oliveira Vigier, Yannick Pouilloux, Joël BarraultAbstract:Abstract The hydrogenation of methyl oleate (methyl cis-9-octadecenoate) to oleyl Alcohol (methyl cis-9-octadecen-1-ol) was studied in the presence of a bimetallic CoSn supported over zinc oxide catalyst in a stainless steel batch reactor at 270 °C and 8.0 MPa of hydrogen. The active species in the reduction of methyl oleate into Unsaturated Alcohols was CoSn2. In order to increase the amount of these active species the nature of the precursor salts was studied. These results have shown that the carbonyl cobalt precursor is the optimum salt for the hydrogenation of methyl oleate into Unsaturated Alcohol since the selectivity to Unsaturated Alcohol reached 55% at 80% of conversion. Moreover, the selectivity is governed by the reduction of the heavy esters (oleyl oleate and oleyl stearate) formed, which can occur in the presence of small Co–Sn2 particles, well dispersed on the catalyst surface and with a high surface content.
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selective hydrogenation of methyl oleate into Unsaturated Alcohols relationships between catalytic properties and composition of cobalt tin catalysts
Catalysis Today, 2000Co-Authors: Yannick Pouilloux, F Autin, Joël BarraultAbstract:Abstract The selective hydrogenation of methyl oleate into oleyl Alcohol, intermediate in the formulation of surfactant agents, is carried out over bimetallic catalysts containing cobalt and tin. However the tin content modifies the rates of the hydrogenation of the esters (methyl oleate and oleyl oleate) and of the side reaction of the transesterification between the methyl oleate and the Alcohol formed. Indeed, the maximum of the Unsaturated Alcohol yield depends on the Sn/metal ratio. The analyses of the catalyst surface by XPS have shown that there are coexistence of metallic particles (Co 0 ) and/or oxides (CoO) with two different tin oxides (SnO x , SnO y ), the SnO x species being close to zerovalent metallic particles. It is suggested that (1) [Co 0 ⋯(SnO x ) 2 ] should be the active sites for the selective hydrogenation of ester, (2) the SnO y species favor the reaction of transesterification and (3) the free metallic particles favor the hydrogenation of ethylenic bonds. On the other hand, the preparation method of the catalyst and the nature of the support modify the surface composition of the solid. The use of alumina or zinc oxide lead to the same yield of Unsaturated Alcohol whereas silica which has much more metallic Co 0 species gives a low activity due to a large tin enrichment. Over CoSn catalysts reduced with NaBH 4 , owing to the formation of cobalt aluminate, a small content of metallic cobalt is observed. The preparation of CoSn catalyst via a sol–gel method improves the homogeneity and the dispersion of the active sites. But the strong interactions between cobalt and the support do not allow the formation of both metallic cobalt and mixed active centers (Co 0 , SnO x ). Furthermore, some kinetic studies obtained with cobalt catalysts show that (1) the transesterification reaction is faster than the hydrogenation of esters, (2) the presence of methanol issued from the hydrogenation and from the transesterification strongly modifies the oleyl oleate hydrogenation.
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Preparation of oleyl Alcohol from the hydrogenation of methyl oleate in the presence of cobalt-tin catalysts
Applied Catalysis A: General, 1998Co-Authors: Yannick Pouilloux, A. Piccirilli, F Autin, Claude Guimon, Joël BarraultAbstract:Abstract The hydrogenation of methyl oleate into oleyl Alcohol was studied in the presence of a CoSn catalyst at 270°C and 8.0 MPa. The selectivity of the CoSn catalyst to oleyl Alcohol is comparable to that of the RuSn catalyst but the CoSn catalyst is less active. The activity and the selectivity to Unsaturated Alcohol was maximum for an atomic Sn/Co ratio of 1. Nevertheless, the side reaction, the transesterification between methyl oleate and Alcohol, still occurs in the presence of CoSn catalysts. The method of preparation influenced the activity, impregnation and reduction with sodium borohydride dry>impregnation>sol–gel technique, but the oleyl Alcohol yields, obtained over the catalyst reduced with sodium borohydride or over the catalyst prepared by a sol–gel technique, are similar. From XPS analysis, Co0 and two tin-oxide species were identified at the surface of the CoSnB/Al2O3 catalyst after reduction with sodium borohydride. The addition of tin species does not modify the surface cobalt content. The reduction with sodium borohydride increased the reducibility of the metal oxide species.
Utpal K Singh - One of the best experts on this subject based on the ideXlab platform.
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liquid phase citral hydrogenation over sio2 supported group viii metals
Journal of Catalysis, 2001Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Abstract Liquid-phase citral hydrogenation over SiO 2 -supported Group VIII metals at 300 K and 1 atm was studied in the absence of all transport limitations as verified by the Madon–Boudart test and the Weisz–Prater criterion. The initial TOF (turnover frequency) for citral hydrogenation varied by three orders of magnitude and exhibited the following trend: Pd>Pt>Ir>Os>Ru>Rh>Ni>Co⪢Fe (no activity was detected over Fe/SiO 2 ). When TOF is correlated with percentage d-character, a volcano plot results. There are significant differences in product distribution among the different metals, with Os, Ru, and Co exhibiting high selectivity toward the Unsaturated Alcohol isomers (geraniol and nerol), while Rh, Ni, and Pd were more selective for citronellal and isopulegol. The variation in product distribution among the various metals is rationalized on the basis of the d-band widths that affect the relative importance of the stabilizing two-electron interactions and destabilizing four-electron interactions. With the exception of Ni/SiO 2 , all catalysts exhibited substantial deactivation that was attributed to inhibition by adsorbed CO produced by the decomposition of either citral or the Unsaturated Alcohol. In contrast, Ni/SiO 2 exhibited an initially low, stable TOF during the first 7 h that then increased fourfold and again remained constant to 84% citral conversion, at which point the run was terminated.
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influence of metal support interactions on the kinetics of liquid phase citral hydrogenation
Journal of Molecular Catalysis A-chemical, 2000Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Abstract The kinetics of liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) on Pt/TiO 2 catalysts were studied between 298–423 K and 7–21 atm H 2 and compared to those reported earlier for Pt/SiO 2 catalysts. The kinetic data were shown to be free of transport limitations by application of the Madon–Boudart test and the Weisz–Prater criterion. Near zero- and first-order kinetics were observed for the initial rate of citral hydrogenation over the Pt/TiO 2 -LTR ( T red =473 K ) and Pt/SiO 2 catalysts with respect to citral concentration and hydrogen pressure, respectively. In contrast, each dependency dropped by about one order with Pt/TiO 2 -HTR ( T red =773 K ) catalysts as they were negative first-order on citral concentration and near zero-order on hydrogen pressure. Furthermore, the initial rates over Pt/TiO 2 -LTR and Pt/SiO 2 exhibited an activity minimum as temperature increased whereas conventional Arrhenius behavior was exhibited by Pt/TiO 2 -HTR with an activation energy of 18 kcal/mol. Pt/TiO 2 -LTR and HTR catalysts initially exhibited 90% selectivity to the Unsaturated Alcohol as compared to 40% for hydrogenation over Pt/SiO 2 . Metal–support interactions (MSI) resulted in a dramatic enhancement in specific activity at 373 K, 20 atm H 2 and 1 M citral in hexane as Pt/TiO 2 -HTR exhibited a turnover frequency of 1.0 compared to 0.02 s −1 for Pt/TiO 2 -LTR and 0.004 s −1 for Pt/SiO 2 . The reaction kinetics with Pt/TiO 2 -HTR in the differential conversion regime were described by a conventional Langmuir–Hinshelwood model assuming quasi-equilibrium for reactant adsorption, competitive adsorption between citral and hydrogen, and addition of the first H atom as the rate determining step. The reaction rate at higher conversions was modeled by invoking a decarbonylation reaction similar to that proposed earlier for this reaction over Pt/SiO 2 catalysts to explain any observed deactivation.
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liquid phase hydrogenation of citral over pt sio2 catalysts i temperature effects on activity and selectivity
Journal of Catalysis, 2000Co-Authors: Utpal K Singh, Albert M VanniceAbstract:Liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) over Pt/SiO2 catalysts was studied in the temperature and pressure ranges 298–423 K and 7–21 atm, respectively. The reaction kinetics were shown to be free of artifacts arising from transport limitations and poisoning effects. The reaction rate in hexane as the solvent exhibited an activity minimum at 373 K. The initial turnover frequency for citral disappearance over 1.44% Pt/SiO2 catalyst at 20 atm H2 pressure decreased from 0.19 s−1 at 298 K to 0.02 s−1 at 373 K, but exhibited normal Arrhenius behavior between 373 and 423 K with an activation energy of 7 kcal/mol. Reaction at 298 K produced substantial deactivation, with the rate decreasing by more than an order of magnitude during the first 4 h of reaction; however, reaction at temperatures greater than 373 K exhibited negligible deactivation and a constant rate up to citral conversions greater than 70%. These unusual temperature effects were modeled using Langmuir–Hinshelwood kinetics invoking dissociative adsorption of hydrogen, competitive adsorption between hydrogen and the organic compounds, and addition of the second hydrogen atom to each reactant as the rate-determining step. Decomposition of the Unsaturated Alcohol (either geraniol or nerol) was proposed to occur concurrently with the hydrogenation steps to yield adsorbed CO and carbonaceous species which cause the deactivation, but at higher temperatures these species could be removed from the Pt surface by desorption or rapid hydrogenation, respectively. The activity minimum observed in the present study is attributed to the relative rates of the Alcohol decomposition reaction and CO desorption, with the decomposition reaction having an activation barrier lower than that for CO desorption.
Philippe Sautet - One of the best experts on this subject based on the ideXlab platform.
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influence of sn additives on the selectivity of hydrogenation of α β Unsaturated aldehydes with pt catalysts a density functional study of molecular adsorption
Journal of Catalysis, 2003Co-Authors: Francoise Delbecq, Philippe SautetAbstract:Abstract In this study, the adsorption and the reactive properties of α - β -Unsaturated aldehydes are studied by means of density functional calculations (DFT) on two well-defined PtSn alloy surfaces, p(2×2) Pt 3 Sn(111) and ( 3 × 3 )R30 ° Pt 2 Sn(111). First the electronic structure of the bulk alloys is determined: a charge transfer occurs from Sn to Pt, the work function decreases, and the d-band center is shifted away from the Fermi level. Then various adsorption structures of acrolein (propenal), crotonaldehyde (2-butenal), and prenal (3-methyl, 2-butenal) are considered on the two alloys. The results are compared with those obtained on Pt(111). A large decrease of the adsorption energies is observed for the alloys. For acrolein, there is almost no change in the best adsorption modes, the adsorption through the CC bond being predominant. This explains why the selectivity of the acrolein hydrogenation is not changed much when PtSn alloys and Pt are compared. For prenal on the contrary, only the atop mode is stable on the alloys, whereas a structure parallel to the surface is the most stable one on Pt. This explains the modified reaction selectivity with a larger amount of Unsaturated Alcohol in the products in the case of the Sn alloys.
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a density functional study of adsorption structures of Unsaturated aldehydes on pt 111 a key factor for hydrogenation selectivity
Journal of Catalysis, 2002Co-Authors: Francoise Delbecq, Philippe SautetAbstract:Various adsorption structures of acrolein (propenal), crotonaldehyde (2-butenal), and prenal (3-methyl-2-butenal) on Pt(111) are compared by means of first-principle density functional theory calculations (DFT). Methyl substituents are added one by one at the C1 carbon of the CC–CO frame and the substitution induces a general decrease in the adsorption energy. Over a large range of coverages, acrolein shows its main interaction with the surface with the CC bond, with an eventual additional weak interaction with the oxygen atom. This could clearly result in a predominant hydrogenation of the CC bond, as was seen experimentally. The influence of the substituents is subtle in the case of crotonaldehyde but clear for prenal. In that case, at low coverage a flat adsorption mode by both the CC and the CO bonds is favored. This larger implication of the CO bond in the adsorption is a first explanation for the higher selectivity in Unsaturated Alcohol during the hydrogenation of prenal compared with acrolein. Additionally, if high coverage is considered, the prenal molecule is too large to keep a flat adsorption mode and it can switch to a vertical geometry, interacting with the surface by the oxygen atom, while acrolein remains bonded by the CC bond. Such a vertical structure prevents CC hydrogenation and could also explain the increased selectivity to Unsaturated Alcohol.
