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Gabor A. Somorjai - One of the best experts on this subject based on the ideXlab platform.
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platinum nanoparticle shape effects on benzene hydrogenation selectivity
Nano Letters, 2007Co-Authors: Kaitlin M. Bratlie, Kyriakos Komvopoulos, Peidong Yang, Hyunjoo Lee, Gabor A. SomorjaiAbstract:Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C−H···Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and Cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 ± 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and Cyclohexene production are 8.3 ± 0.2 and 12.2 ± 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnov...
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platinum nanoparticle shape effects on benzene hydrogenation selectivity
Nano Letters, 2007Co-Authors: Kaitlin M. Bratlie, Kyriakos Komvopoulos, Peidong Yang, Hyunjoo Lee, Gabor A. SomorjaiAbstract:Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and Cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and Cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.
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in situ sum frequency generation vibrational spectroscopy observation of a reactive surface intermediate during high pressure benzene hydrogenation
Journal of Physical Chemistry B, 2006Co-Authors: Kaitlin M. Bratlie, Lucio D Flores, Gabor A. SomorjaiAbstract:Sum frequency generation surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to identify a reactive surface intermediate in situ during hydrogenation of benzene on a Pt(111) single crystal surface at Torr pressures. Upon adsorption at 310 K, both chemisorbed and physisorbed benzene coexist on the surface, a result which has not previously been observed. Kinetic measurements show a linear compensation effect for the production of both cyclohexane and Cyclohexene. From these data the isokinetic temperature was identified and correlated to the chemisorbed benzene species, which were probed by means of vibrational spectroscopy. Additionally, chemisorbed benzene was determined to be a reactive intermediate, which is critical for hydrogenation.
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1 3 and 1 4 cyclohexadiene reaction intermediates in Cyclohexene hydrogenation and dehydrogenation on pt 111 crystal surface a combined reaction kinetics and surface vibrational spectroscopy study using sum frequency generation
Journal of Molecular Catalysis A-chemical, 1999Co-Authors: Gabor A. Somorjai, Kyle Kung, Jouko Lahtinen, Ron Y ShenAbstract:Abstract The hydrogenation and dehydrogenation reactions of Cyclohexene on Pt(111) surface were investigated by surface vibrational spectroscopy via sum frequency generation (SFG) both under ultrahigh vacuum (UHV) and high pressure conditions with 10 Torr Cyclohexene and various hydrogen pressures up to 590 Torr. Under UHV, Cyclohexene on Pt(111) undergoes a change from π/σ-bonded, σ-bonded, and c-C6H9 surface species to adsorbed benzene when the surface was heated. A site-blocking effect was observed at saturation coverage of Cyclohexene and caused the dehydrogenation to shift to higher surface temperature. At high pressures, however, none of the species observed in UHV condition were seen. 1,4-cyclohexadiene (CHD) was found to be the major species on the surface at 295 K even in the presence of nearly 600 Torr of hydrogen. Hydrogenation was the only detectable reaction at the temperature range between 300–400 K with 1,3-CHD on the surface as revealed by SFG. Further increasing surface temperature results in a decrease in hydrogenation reaction rate and an increase in dehydrogenation reaction rate with both 1,3-CHD and 1,4-CHD detectable on the surface simultaneously. Monitoring the reaction kinetics and the chemical nature of surface species together allows us to postulate a reaction mechanism: Cyclohexene hydrogenates to cyclohexane via a 1,3-CHD intermediate, and dehydrogenates to benzene through both 1,4-CHD and 1,3-CHD intermediates. Both 1,3- and 1,4-CHD dehydrogenate to benzene at sufficiently high temperature on Pt(111).
Kaitlin M. Bratlie - One of the best experts on this subject based on the ideXlab platform.
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platinum nanoparticle shape effects on benzene hydrogenation selectivity
Nano Letters, 2007Co-Authors: Kaitlin M. Bratlie, Kyriakos Komvopoulos, Peidong Yang, Hyunjoo Lee, Gabor A. SomorjaiAbstract:Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C−H···Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and Cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 ± 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and Cyclohexene production are 8.3 ± 0.2 and 12.2 ± 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnov...
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platinum nanoparticle shape effects on benzene hydrogenation selectivity
Nano Letters, 2007Co-Authors: Kaitlin M. Bratlie, Kyriakos Komvopoulos, Peidong Yang, Hyunjoo Lee, Gabor A. SomorjaiAbstract:Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and Cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and Cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.
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in situ sum frequency generation vibrational spectroscopy observation of a reactive surface intermediate during high pressure benzene hydrogenation
Journal of Physical Chemistry B, 2006Co-Authors: Kaitlin M. Bratlie, Lucio D Flores, Gabor A. SomorjaiAbstract:Sum frequency generation surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to identify a reactive surface intermediate in situ during hydrogenation of benzene on a Pt(111) single crystal surface at Torr pressures. Upon adsorption at 310 K, both chemisorbed and physisorbed benzene coexist on the surface, a result which has not previously been observed. Kinetic measurements show a linear compensation effect for the production of both cyclohexane and Cyclohexene. From these data the isokinetic temperature was identified and correlated to the chemisorbed benzene species, which were probed by means of vibrational spectroscopy. Additionally, chemisorbed benzene was determined to be a reactive intermediate, which is critical for hydrogenation.
Joao Costa Pessoa - One of the best experts on this subject based on the ideXlab platform.
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oxidovanadium iv complexes of tetradentate ligands encapsulated in zeolite y as catalysts for the oxidation of styrene Cyclohexene and methyl phenyl sulfide
European Journal of Inorganic Chemistry, 2011Co-Authors: Mannar R Maurya, Priyanka Saini, Amit Kumar, Joao Costa PessoaAbstract:The reaction of oxidovanadium(IV)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I), N,N′-propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) and H2pydx-1,2-pn (III) in methanol heated at reflux leads to the formation of the corresponding complexes, abbreviated herein as [VIVO(pydx-en)]-Y (4), [VIVO(pydx-1,3-pn)]-Y (5) and [VIVO(pydx-1,2-pn)]-Y (6) in the supercages of zeolite-Y. The neat complexes [VIVO(pydx-en)] (1), [VIVO(pydx-1,3-pn)] (2) and [VIVO(pydx-1,2-pn)] (3) were also prepared. Spectroscopic studies (IR, UV/Vis and EPR), elemental analyses, thermal studies, field-emission scanning electron micrographs (FESEM) and X-ray diffraction patterns were used to characterize these complexes. Oxidations of styrene, Cyclohexene and methyl phenyl sulfide were investigated using these complexes as catalyst precursors in the presence of H2O2 as oxidant. Under the optimized reaction conditions, a maximum of 85.5 % conversion of styrene was obtained with 4, 84.6 % conversion with 5 and 82.9 % conversion with 6 in 6 h of reaction time. The selectivity of the various products was similar for the catalyst precursors 4–6 and followed the order: benzaldehyde > 1-phenylethane-1,2-diol > benzoic acid > phenyl acetaldehyde. With Cyclohexene, a maximum conversion of 95.9 % was achieved with 4, 94.5 % with 5 and 94.2 % conversion with 6, also in 6 h of reaction time. The selectivity of the various products was similar for the three catalysts: 2-cyclohexen-1-one > 2-cyclohexen-1-ol > cyclohexane-1,2-diol. The oxidation of methyl phenyl sulfide was achieved with 4, 5 and 6 in 2.5 h of reaction time with 85.5, 82.1 and 80 % conversion, with higher selectivity towards sulfoxide. Overall, the encapsulated catalysts were significantly more active than their neat counterparts and have the further advantage of being recyclable. No relevant difference in activity was found due to a change in the diamine in the Schiff base ligands I–III. UV/Vis and 51V NMR spectroscopic experiments with 1 confirmed the plausible formation of VVO(O2)L as intermediates in the catalytic oxidations.
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zeolite encapsulated copper ii complexes of pyridoxal based tetradentate ligands for the oxidation of styrene Cyclohexene and methyl phenyl sulfide
European Journal of Inorganic Chemistry, 2007Co-Authors: Mannar R Maurya, Baljit Singh, Pedro Adao, Fernando Avecilla, Joao Costa PessoaAbstract:Interaction of copper(II)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I) and N,N′-propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) ligands in refluxing methanol leads to the formation of the corresponding complexes, abbreviated herein as [Cu(pydx-en)]-Y (3) and [Cu(pydx-1,3-pn)]-Y (4), in the supercages of zeolite-Y. The neat complexes, [Cu(pydx-en)] (1) and [Cu(pydx-1,3-pn)] (2), have also been prepared with these ligands. Spectroscopic studies (IR, UV/Vis and EPR), elemental analyses, thermal studies, field emission scanning electron micrographs (FE-SEM) and X-ray diffraction patterns have been used to characterise these complexes. The crystal and molecular structures of 1 and of 2·CH3OH, have been determined, confirming the ONNO binding mode of the ligands. The geometry around the metal ion is very slightly distorted square-planar in 1 and distorted square-pyramidal in 2. The encapsulated complexes catalyse the oxidation, by H2O2 and tert-butyl hydroperoxide, of styrene, Cyclohexene and thioanisole efficiently. Under optimised reaction conditions, the oxidation of styrene catalysed by 3 and 4 gave 23.6 % and 28.0 % conversion, respectively, using tert-butyl hydroperoxide as oxidant, where styrene oxide, benzaldehyde, benzoic acid and phenylacetaldehyde are the major products. Better conversions have been obtained using H2O2 as oxidant. Oxidation of Cyclohexene catalysed by these complexes gave Cyclohexene oxide, 2-cyclohexen-1-ol, cyclohexane-1,2-diol and 2-cyclohexen-1-one as the major products. A maximum of 90.1 % conversion of Cyclohexene with 3 and 83.0 % with 4 was obtained under optimised conditions. Similarly, a maximum of 80.3 % conversion of methyl phenyl sulfide with 3 and 81.0 % with 4 was observed, where the selectivity of the major product methyl phenyl sulfoxide was found to be about 60 %. Tests for the recyclability and heterogeneity of the reactions have also been carried out, and the results indicate their recyclability. A possible reaction mechanism has been proposed by titrating a methanol solution of 1 and 2 with H2O2 to identify the possible intermediates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Margarita Sanchotello - One of the best experts on this subject based on the ideXlab platform.
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isobaric vapor liquid equilibria for binary and ternary mixtures with cyclohexane Cyclohexene and methyl isobutyl ketone at 100 kpa
Journal of Chemical & Engineering Data, 2010Co-Authors: Beatriz Marrufo, Sonia Loras, Margarita SanchotelloAbstract:Consistent vapor−liquid equilibrium (VLE) data at 100 kPa have been determined for the ternary system cyclohexane + Cyclohexene + methyl isobutyl ketone and two constituent binary systems: cyclohexane + methyl isobutyl ketone and Cyclohexene + methyl isobutyl ketone. Both binary systems show positive deviations from ideal behavior and do not present an azeotrope. The VLE data have been correlated by the Wilson, UNIQUAC, and NRTL equations. The ternary system does not present an azeotrope and is well predicted from binary interaction parameters. Prediction with the UNIFAC method has also been obtained.
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isobaric vapor liquid equilibria for binary and ternary mixtures with cyclohexane Cyclohexene and 2 methoxyethanol at 100 kpa
Journal of Chemical & Engineering Data, 2010Co-Authors: Beatriz Marrufo, Sonia Loras, Margarita SanchotelloAbstract:Consistent vapor−liquid equilibria (VLE) data at 100 kPa have been determined for the ternary system cyclohexane + Cyclohexene + 2-methoxyethanol and two constituent binary systems: cyclohexane + 2-methoxyethanol and Cyclohexene + 2-methoxyethanol. Both binary systems deviate remarkably from ideal behavior presenting a minimum boiling point azeotrope. The VLE data have been correlated by the Wilson, UNIQUAC, and NRTL equations. The ternary system does not present an azeotrope and is well predicted from binary interaction parameters. Prediction with the UNIFAC method has been also obtained.
Mannar R Maurya - One of the best experts on this subject based on the ideXlab platform.
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oxidovanadium iv complexes of tetradentate ligands encapsulated in zeolite y as catalysts for the oxidation of styrene Cyclohexene and methyl phenyl sulfide
European Journal of Inorganic Chemistry, 2011Co-Authors: Mannar R Maurya, Priyanka Saini, Amit Kumar, Joao Costa PessoaAbstract:The reaction of oxidovanadium(IV)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I), N,N′-propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) and H2pydx-1,2-pn (III) in methanol heated at reflux leads to the formation of the corresponding complexes, abbreviated herein as [VIVO(pydx-en)]-Y (4), [VIVO(pydx-1,3-pn)]-Y (5) and [VIVO(pydx-1,2-pn)]-Y (6) in the supercages of zeolite-Y. The neat complexes [VIVO(pydx-en)] (1), [VIVO(pydx-1,3-pn)] (2) and [VIVO(pydx-1,2-pn)] (3) were also prepared. Spectroscopic studies (IR, UV/Vis and EPR), elemental analyses, thermal studies, field-emission scanning electron micrographs (FESEM) and X-ray diffraction patterns were used to characterize these complexes. Oxidations of styrene, Cyclohexene and methyl phenyl sulfide were investigated using these complexes as catalyst precursors in the presence of H2O2 as oxidant. Under the optimized reaction conditions, a maximum of 85.5 % conversion of styrene was obtained with 4, 84.6 % conversion with 5 and 82.9 % conversion with 6 in 6 h of reaction time. The selectivity of the various products was similar for the catalyst precursors 4–6 and followed the order: benzaldehyde > 1-phenylethane-1,2-diol > benzoic acid > phenyl acetaldehyde. With Cyclohexene, a maximum conversion of 95.9 % was achieved with 4, 94.5 % with 5 and 94.2 % conversion with 6, also in 6 h of reaction time. The selectivity of the various products was similar for the three catalysts: 2-cyclohexen-1-one > 2-cyclohexen-1-ol > cyclohexane-1,2-diol. The oxidation of methyl phenyl sulfide was achieved with 4, 5 and 6 in 2.5 h of reaction time with 85.5, 82.1 and 80 % conversion, with higher selectivity towards sulfoxide. Overall, the encapsulated catalysts were significantly more active than their neat counterparts and have the further advantage of being recyclable. No relevant difference in activity was found due to a change in the diamine in the Schiff base ligands I–III. UV/Vis and 51V NMR spectroscopic experiments with 1 confirmed the plausible formation of VVO(O2)L as intermediates in the catalytic oxidations.
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zeolite encapsulated copper ii complexes of pyridoxal based tetradentate ligands for the oxidation of styrene Cyclohexene and methyl phenyl sulfide
European Journal of Inorganic Chemistry, 2007Co-Authors: Mannar R Maurya, Baljit Singh, Pedro Adao, Fernando Avecilla, Joao Costa PessoaAbstract:Interaction of copper(II)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I) and N,N′-propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) ligands in refluxing methanol leads to the formation of the corresponding complexes, abbreviated herein as [Cu(pydx-en)]-Y (3) and [Cu(pydx-1,3-pn)]-Y (4), in the supercages of zeolite-Y. The neat complexes, [Cu(pydx-en)] (1) and [Cu(pydx-1,3-pn)] (2), have also been prepared with these ligands. Spectroscopic studies (IR, UV/Vis and EPR), elemental analyses, thermal studies, field emission scanning electron micrographs (FE-SEM) and X-ray diffraction patterns have been used to characterise these complexes. The crystal and molecular structures of 1 and of 2·CH3OH, have been determined, confirming the ONNO binding mode of the ligands. The geometry around the metal ion is very slightly distorted square-planar in 1 and distorted square-pyramidal in 2. The encapsulated complexes catalyse the oxidation, by H2O2 and tert-butyl hydroperoxide, of styrene, Cyclohexene and thioanisole efficiently. Under optimised reaction conditions, the oxidation of styrene catalysed by 3 and 4 gave 23.6 % and 28.0 % conversion, respectively, using tert-butyl hydroperoxide as oxidant, where styrene oxide, benzaldehyde, benzoic acid and phenylacetaldehyde are the major products. Better conversions have been obtained using H2O2 as oxidant. Oxidation of Cyclohexene catalysed by these complexes gave Cyclohexene oxide, 2-cyclohexen-1-ol, cyclohexane-1,2-diol and 2-cyclohexen-1-one as the major products. A maximum of 90.1 % conversion of Cyclohexene with 3 and 83.0 % with 4 was obtained under optimised conditions. Similarly, a maximum of 80.3 % conversion of methyl phenyl sulfide with 3 and 81.0 % with 4 was observed, where the selectivity of the major product methyl phenyl sulfoxide was found to be about 60 %. Tests for the recyclability and heterogeneity of the reactions have also been carried out, and the results indicate their recyclability. A possible reaction mechanism has been proposed by titrating a methanol solution of 1 and 2 with H2O2 to identify the possible intermediates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
