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Saim Ozkar - One of the best experts on this subject based on the ideXlab platform.
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ceria supported Rhodium nanoparticles superb catalytic activity in hydrogen generation from the hydrolysis of ammonia borane
Applied Catalysis B-environmental, 2016Co-Authors: Serdar Akbayrak, Yalcin Tonbul, Saim OzkarAbstract:Abstract We investigated the effect of various oxide supports on the catalytic activity of Rhodium nanoparticles in hydrogen generation from the hydrolysis of ammonia borane. Among the oxide supports (CeO2, SiO2, Al2O3, TiO2, ZrO2, HfO2) ceria provides the highest catalytic activity for the Rhodium(0) nanoparticles in the hydrolysis of ammonia borane. Rhodium(0) nanoparticles supported on nanoceria (Rh0/CeO2) were prepared by the impregnation of Rhodium(III) ions on the surface of ceria followed by their reduction with sodium borohydride in aqueous solution at room temperature. They were isolated from the reaction solution by centrifugation and characterized by a combination of advanced analytical techniques. The catalytic activity of Rh0/CeO2 samples with various Rhodium loading in the range of 0.1–4.0% wt. Rh was also tested in hydrogen generation from the hydrolysis of ammonia borane at room temperature. The highest catalytic activity was achieved by using 0.1% wt. Rhodium loaded nanoceria. The resulting Rh0/CeO2 with a metal loading of 0.1% wt. Rh show superb catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a record turnover frequency value (TOF) of 2010 min−1 at 25.0 ± 0.1 °C. The superb catalytic activity of Rh0/CeO2 is ascribed to the reducible nature of ceria. The reduction of cerium(IV) to cerium(III) leads to a build-up of negative charge on the oxide surface which favors the bonding of Rhodium(0) nanoparticles on the surface and, thus, their catalytic activity. Rh0/CeO2 are also reusable catalysts preserving 67% of their initial catalytic activity even after the fifth use in hydrogen generation from the hydrolysis of ammonia borane at room temperature (TOF = 1350 min−1. The work reported here also includes the kinetic studies depending on the temperature to determine the activation energy (Ea = 43 ± 2 kJ/mol) and the effect of catalyst concentration on the rate of hydrolysis of ammonia borane.
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Rhodium 0 nanoparticles supported on nanosilica highly active and long lived catalyst in hydrogen generation from the methanolysis of ammonia borane
Applied Catalysis B-environmental, 2016Co-Authors: Derya Ozhava, Saim OzkarAbstract:Abstract Nanosilica stabilized Rhodium(0) nanoparticles (Rh(0)/nanoSiO 2 ), in situ formed from the reduction of Rhodium(II) octanoate impregnated on the surface of nanosilica, are active catalyst in hydrogen generation from the methanolysis of ammonia borane at room temperature. Monitoring the hydrogen evolution enables us to follow the kinetics of nanoparticles formation. The resulting sigmoidal kinetic curves are analyzed by using the 2-step mechanism of the slow, continuous nucleation and autocatalytic surface growth. By using the temperature dependent kinetic data, we could calculate the activation energy for the nucleation and autocatalytic surface growth of Rhodium(0) nanoparticles as well as for the catalytic methanolysis of ammonia borane. Rh(0)/nanoSiO 2 could be isolated and characterized by a combination of advanced analytical techniques including XRD, TEM, EDX, XPS, and N 2 adsorption–desorption. The results reveal that Rhodium(0) nanoparticles are highly dispersed on nanosilica surface and have tunable particle size depending on the initial metal concentration. An increase in the mean particle size of Rhodium(0) nanoparticles is observed when the initial metal concentration increases. Rh(0)/nanoSiO 2 are highly active and long lived catalyst in hydrogen generation from the methanolysis providing an exceptional initial turnover frequency of TOF = 168 min −1 (504 min −1 corrected for the surface atoms) at 25.0 ± 0.5 °C, which is the highest value ever reported for Rhodium catalysts. An inverse dependence of TOF on the initial Rhodium concentration is observed and ascribed to the increasing size of Rhodium(0) nanoparticles. Carbon disulfide poisoning and filtration experiments unequivocally demonstrate that Rhodium(0) nanoparticles are the true heterogeneous catalyst in hydrogen generation from the methanolysis of ammonia borane.
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hydrogen generation from the hydrolysis of hydrazine borane catalyzed by Rhodium 0 nanoparticles supported on hydroxyapatite
International Journal of Hydrogen Energy, 2012Co-Authors: Derya Celik, Mehmet Zahmakiran, Senem Karahan, Saim OzkarAbstract:Abstract Herein, we report the preparation and characterization of Rhodium(0) nanoparticles supported on hydroxyapatite (Ca10(OH)2(PO4)6, HAP) and their catalytic use in the hydrolysis of hydrazine-borane, which attracts recent attention as promising hydrogen storage materials. Hydroxyapatite supported Rhodium(0) nanoparticles were readily prepared by the hydrazine-borane reduction of Rhodium(III)-exchanged hydroxyapatite in situ during the hydrolysis of hydrazine-borane at room temperature. Characterization of the resulting material by ICP–OES, TEM, SEM, EDX, XRD, XPS spectroscopies and N2 adsorption–desorption technique, which shows the formation of Rhodium(0) nanoparticles well dispersed on hydroxyapatite support. The catalytic performance of these new supported Rhodium(0) nanoparticles in terms of activity, lifetime and reusability was tested in the hydrolysis of hydrazine-borane. They were found to be highly active, long-lived and reusable catalyst in this important catalytic reaction even at low temperatures and high initial [substrate]/[catalyst] conditions. This report also includes the detailed kinetic study of the hydrolysis of hydrazine-borane catalyzed by hydroxyapatite supported Rhodium(0) nanoparticles depending on the catalyst concentration, substrate concentration, and temperature.
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zeolite confined Rhodium 0 nanoclusters as highly active reusable and long lived catalyst in the methanolysis of ammonia borane
Applied Catalysis B-environmental, 2010Co-Authors: Salim Caliskan, Mehmet Zahmakiran, Saim OzkarAbstract:Abstract Addressed herein is the preparation, characterization and the catalytic use of zeolite confined Rhodium(0) nanoclusters in the methanolysis of ammonia-borane. Rhodium(0) nanoclusters could be generated in zeolite-Y by a two-step procedure: (i) incorporation of Rhodium(III) cations into the zeolite-Y by ion-exchange and (ii) reduction of Rhodium(III) ions within the zeolite cages by sodium borohydride in aqueous solution, followed by filtration and dehydration by heating to 550 °C under 10 −4 Torr. Zeolite confined Rhodium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by ICP-OES, XRD, SEM, EDX, HR-TEM, XPS and N 2 adsorption–desorption technique. The zeolite confined Rhodium(0) nanoclusters are isolable, bottleable, redispersible and reusable as an active catalyst in the methanolysis of ammonia-borane even at low temperatures. They provide exceptional catalytic activity with an average value of TOF = 380 h −1 and unprecedented lifetime with 74,300 turnovers in the methanolysis of ammonia-borane at 25 ± 0.1 °C. The work reported here also includes the full experimental details of the collection of a wealth of previously unavailable kinetic data to determine the rate law, and activation parameters ( E a , Δ H ≠ and Δ S ≠ ) for the catalytic methanolysis of ammonia-borane.
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water soluble laurate stabilized Rhodium 0 nanoclusters catalyst with unprecedented catalytic lifetime in the hydrolytic dehydrogenation of ammonia borane
Applied Catalysis A-general, 2009Co-Authors: Feyyaz Durap, Mehmet Zahmakiran, Saim OzkarAbstract:Abstract Herein we report, for the first time, the preparation and characterization of water soluble Rhodium(0) nanoclusters stabilized by laurate (dodecanoate) anion and their catalytic activity in the hydrolysis of ammonia-borane. The water soluble laurate-stabilized Rhodium(0) nanoclusters were prepared from the reduction of Rhodium(III) chloride by dimethylamine-borane in solution containing sodium laurate at room temperature. The water soluble laurate-stabilized Rhodium(0) nanoclusters in average size of 5.2 ± 2.7 nm could be isolated from the reaction solution and characterized by using UV–vis, TEM, XPS, XRD and FTIR spectroscopic methods. Catalytic activity of Rhodium(0) nanoclusters was tested in the hydrolysis of ammonia-borane. They show exceptional catalytic activity and unprecedented catalytic lifetime in this reaction. They provide a TOF value of 200 mol H 2 /mol Rh min and 80,000 turnovers in the hydrolysis of ammonia-borane in air at 25.0 ± 0.1 °C.
Ken Tanaka - One of the best experts on this subject based on the ideXlab platform.
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Enantioselective Helicene Synthesis by Rhodium-Catalyzed [2+2+2] Cycloadditions
Bulletin of the Chemical Society of Japan, 2015Co-Authors: Ken Tanaka, Yuki Kimura, Koichi MurayamaAbstract:The highly enantioselective synthesis of functionalized helicenes and helicene-like molecules have been achieved via Rhodium-catalyzed [2+2+2] cycloaddition reactions. The Rhodium-catalyzed enantio...
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oxidative annulation of anilides with internal alkynes using an electron deficient η5 cyclopentadienyl Rhodium iii catalyst under ambient conditions
Advanced Synthesis & Catalysis, 2014Co-Authors: Yuki Hoshino, Yu Shibata, Ken TanakaAbstract:A dinuclear (electron-deficient η5-cyclopentadienyl)Rhodium(III) complex was synthesized on a preparative scale via the Rhodium-catalyzed cross [2+2+1] cyclotrimerization of silylacetylenes and two alkynyl esters, leading to substituted silylfulvenes, followed by reductive complexation with Rhodium(III) chloride in ethanol. The thus obtained dinuclear (electron-deficient η5-cyclopentadienyl)Rhodium(III) complex is a highly active precatalyst for the oxidative annulation of anilides with internal alkynes under ambient conditions (at room temperature under air). A preference for annulation across electron-rich substrates over electron-deficient substrates was observed using this electron-deficient Rhodium(III) complex.
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asymmetric synthesis of axially chiral biaryl diphosphine ligands by Rhodium catalyzed enantioselective intramolecular double 2 2 2 cycloaddition
Organic Letters, 2011Co-Authors: Fumiya Mori, Keiichi Noguchi, Naohiro Fukawa, Ken TanakaAbstract:The concise synthesis of axially chiral biaryl diphosphine ligands by the Rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition of hexayne diphosphine oxides has been achieved. These new chiral diphosphine ligands could be employed as a ligand for the Rhodium-catalyzed asymmetric catalyses.
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cationic Rhodium i complex catalyzed 3 2 and 2 1 cycloadditions of propargyl esters with electron deficient alkynes and alkenes
Journal of the American Chemical Society, 2010Co-Authors: Yu Shibata, Keiichi Noguchi, Ken TanakaAbstract:A cationic Rhodium(I) complex, [Rh(cod)2]SbF6, catalyzes the [3 + 2] cycloaddition of propargyl esters with dialkyl acetylenedicarboxylates in good yields, presumably through carbonyl-stabilized cationic Rhodium(I) alkenylcarbene intermediates. The same Rhodium(I) complex also catalyzes the [2 + 1] cycloaddition (cyclopropanation) of propargyl esters with N,N-disubstituted acrylamides in good yields with perfect diastereoselectivity.
Mehmet Zahmakiran - One of the best experts on this subject based on the ideXlab platform.
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hydrogen generation from the hydrolysis of hydrazine borane catalyzed by Rhodium 0 nanoparticles supported on hydroxyapatite
International Journal of Hydrogen Energy, 2012Co-Authors: Derya Celik, Mehmet Zahmakiran, Senem Karahan, Saim OzkarAbstract:Abstract Herein, we report the preparation and characterization of Rhodium(0) nanoparticles supported on hydroxyapatite (Ca10(OH)2(PO4)6, HAP) and their catalytic use in the hydrolysis of hydrazine-borane, which attracts recent attention as promising hydrogen storage materials. Hydroxyapatite supported Rhodium(0) nanoparticles were readily prepared by the hydrazine-borane reduction of Rhodium(III)-exchanged hydroxyapatite in situ during the hydrolysis of hydrazine-borane at room temperature. Characterization of the resulting material by ICP–OES, TEM, SEM, EDX, XRD, XPS spectroscopies and N2 adsorption–desorption technique, which shows the formation of Rhodium(0) nanoparticles well dispersed on hydroxyapatite support. The catalytic performance of these new supported Rhodium(0) nanoparticles in terms of activity, lifetime and reusability was tested in the hydrolysis of hydrazine-borane. They were found to be highly active, long-lived and reusable catalyst in this important catalytic reaction even at low temperatures and high initial [substrate]/[catalyst] conditions. This report also includes the detailed kinetic study of the hydrolysis of hydrazine-borane catalyzed by hydroxyapatite supported Rhodium(0) nanoparticles depending on the catalyst concentration, substrate concentration, and temperature.
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zeolite confined Rhodium 0 nanoclusters as highly active reusable and long lived catalyst in the methanolysis of ammonia borane
Applied Catalysis B-environmental, 2010Co-Authors: Salim Caliskan, Mehmet Zahmakiran, Saim OzkarAbstract:Abstract Addressed herein is the preparation, characterization and the catalytic use of zeolite confined Rhodium(0) nanoclusters in the methanolysis of ammonia-borane. Rhodium(0) nanoclusters could be generated in zeolite-Y by a two-step procedure: (i) incorporation of Rhodium(III) cations into the zeolite-Y by ion-exchange and (ii) reduction of Rhodium(III) ions within the zeolite cages by sodium borohydride in aqueous solution, followed by filtration and dehydration by heating to 550 °C under 10 −4 Torr. Zeolite confined Rhodium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by ICP-OES, XRD, SEM, EDX, HR-TEM, XPS and N 2 adsorption–desorption technique. The zeolite confined Rhodium(0) nanoclusters are isolable, bottleable, redispersible and reusable as an active catalyst in the methanolysis of ammonia-borane even at low temperatures. They provide exceptional catalytic activity with an average value of TOF = 380 h −1 and unprecedented lifetime with 74,300 turnovers in the methanolysis of ammonia-borane at 25 ± 0.1 °C. The work reported here also includes the full experimental details of the collection of a wealth of previously unavailable kinetic data to determine the rate law, and activation parameters ( E a , Δ H ≠ and Δ S ≠ ) for the catalytic methanolysis of ammonia-borane.
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water soluble laurate stabilized Rhodium 0 nanoclusters catalyst with unprecedented catalytic lifetime in the hydrolytic dehydrogenation of ammonia borane
Applied Catalysis A-general, 2009Co-Authors: Feyyaz Durap, Mehmet Zahmakiran, Saim OzkarAbstract:Abstract Herein we report, for the first time, the preparation and characterization of water soluble Rhodium(0) nanoclusters stabilized by laurate (dodecanoate) anion and their catalytic activity in the hydrolysis of ammonia-borane. The water soluble laurate-stabilized Rhodium(0) nanoclusters were prepared from the reduction of Rhodium(III) chloride by dimethylamine-borane in solution containing sodium laurate at room temperature. The water soluble laurate-stabilized Rhodium(0) nanoclusters in average size of 5.2 ± 2.7 nm could be isolated from the reaction solution and characterized by using UV–vis, TEM, XPS, XRD and FTIR spectroscopic methods. Catalytic activity of Rhodium(0) nanoclusters was tested in the hydrolysis of ammonia-borane. They show exceptional catalytic activity and unprecedented catalytic lifetime in this reaction. They provide a TOF value of 200 mol H 2 /mol Rh min and 80,000 turnovers in the hydrolysis of ammonia-borane in air at 25.0 ± 0.1 °C.
Koichi Murayama - One of the best experts on this subject based on the ideXlab platform.
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Enantioselective Helicene Synthesis by Rhodium-Catalyzed [2+2+2] Cycloadditions
Bulletin of the Chemical Society of Japan, 2015Co-Authors: Ken Tanaka, Yuki Kimura, Koichi MurayamaAbstract:The highly enantioselective synthesis of functionalized helicenes and helicene-like molecules have been achieved via Rhodium-catalyzed [2+2+2] cycloaddition reactions. The Rhodium-catalyzed enantio...
Derya Ozhava - One of the best experts on this subject based on the ideXlab platform.
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Rhodium 0 nanoparticles supported on nanosilica highly active and long lived catalyst in hydrogen generation from the methanolysis of ammonia borane
Applied Catalysis B-environmental, 2016Co-Authors: Derya Ozhava, Saim OzkarAbstract:Abstract Nanosilica stabilized Rhodium(0) nanoparticles (Rh(0)/nanoSiO 2 ), in situ formed from the reduction of Rhodium(II) octanoate impregnated on the surface of nanosilica, are active catalyst in hydrogen generation from the methanolysis of ammonia borane at room temperature. Monitoring the hydrogen evolution enables us to follow the kinetics of nanoparticles formation. The resulting sigmoidal kinetic curves are analyzed by using the 2-step mechanism of the slow, continuous nucleation and autocatalytic surface growth. By using the temperature dependent kinetic data, we could calculate the activation energy for the nucleation and autocatalytic surface growth of Rhodium(0) nanoparticles as well as for the catalytic methanolysis of ammonia borane. Rh(0)/nanoSiO 2 could be isolated and characterized by a combination of advanced analytical techniques including XRD, TEM, EDX, XPS, and N 2 adsorption–desorption. The results reveal that Rhodium(0) nanoparticles are highly dispersed on nanosilica surface and have tunable particle size depending on the initial metal concentration. An increase in the mean particle size of Rhodium(0) nanoparticles is observed when the initial metal concentration increases. Rh(0)/nanoSiO 2 are highly active and long lived catalyst in hydrogen generation from the methanolysis providing an exceptional initial turnover frequency of TOF = 168 min −1 (504 min −1 corrected for the surface atoms) at 25.0 ± 0.5 °C, which is the highest value ever reported for Rhodium catalysts. An inverse dependence of TOF on the initial Rhodium concentration is observed and ascribed to the increasing size of Rhodium(0) nanoparticles. Carbon disulfide poisoning and filtration experiments unequivocally demonstrate that Rhodium(0) nanoparticles are the true heterogeneous catalyst in hydrogen generation from the methanolysis of ammonia borane.
