Browsing by Author "Ozkar, Saim"

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Catalytic Methanolysis of Hydrazine Borane: a New and Efficient Hydrogen Generation System Under Mild Conditions
(Royal Soc Chemistry, 2012) Karahan, Senem; Zahmakiran, Mehmet; Ozkar, Saim
Safe and efficient hydrogen storage is a major obstacle for using hydrogen as an energy carrier. Therefore, intensive efforts have been focused on the development of new materials for chemical hydrogen storage. Of particular importance, hydrazine borane (N2H4BH3) is emerging as one of the most promising solid hydrogen carriers due to its high gravimetric hydrogen storage capacity (15.4 wt%) and low molecular weight. Herein, we report metal catalyzed methanolysis of hydrazine borane (N2H4BH3, HB) as a fast hydrogen generation system under mild conditions. When trace amounts of nickel(II) chloride (NiCl2) is added to the methanol solution of hydrazine borane ([HB]/[Ni] >= 200) the reaction solution releases 3 equiv. of H-2 with a rate of 24 mol H-2 (mol Ni min)(-1) at room temperature. The results reported here also includes (i) identification of the reaction products by using ATR-IR, DP-MS, H-1 and B-11 NMR spectroscopic techniques and the establishment of the reaction stoichiometry, (ii) investigation of the effect of substrate and catalyst concentrations on the hydrogen generation rate to determine the rate law for the catalytic methanolysis of hydrazine borane, (iii) determination of the activation parameters (E-a, Delta H-#, and Delta S-#) for the catalytic methanolysis of hydrazine borane by using the temperature dependent rate data of the hydrogen generation.
Copper(0) Nanoparticles Supported on Silica-Coated Cobalt Ferrite Magnetic Particles: Cost Effective Catalyst in the Hydrolysis of Ammonia-Borane With an Exceptional Reusability Performance
(Amer Chemical Soc, 2012) Kaya, Murat; Zahmakiran, Mehmet; Ozkar, Saim; Volkan, Murvet
Herein we report the development of a new and cost-effective nanocomposite catalyst for the hydrolysis of ammonia-borane (NH3BH3), which is considered to be one of the most promising solid hydrogen carriers because of its high gravimetric hydrogen storage capacity (19.6% wt) and low molecular weight. The new catalyst system consisting of copper nanoparticles supported on magnetic SiO2/CoFe2O4 particles was reproducibly prepared by wet-impregnation of Cu(II) ions on SiO2/CoFe2O4 followed by in situ reduction of the Cu(II) ions on the surface of magnetic support during the hydrolysis of NH3BH3 and characterized by ICP-MS, XRD, XPS, TEM, HR-TEM and N-2 adsorption-desorption technique. Copper nanoparticles supported on silica coated cobalt(II) ferrite SiO2/CoFe2O4 (CuNPs@SCF) act as highly active catalyst in the hydrolysis of ammonia-borane, providing an initial turnover frequency of TOF = 2400 h(-1) at room temperature, which is not only higher than all the non-noble metal catalysts but also higher than the majority of the noble metal based homogeneous and heterogeneous catalysts employed in the same reaction.. More importantly, they were easily recovered by using a permanent magnet in the reactor wall and reused for up, to 10 recycles without losing their inherent catalytic activity significantly, which demonstrates the exceptional reusability of the CuNPs@SCF catalyst.
Dihydrogen Phosphate Stabilized Ruthenium(0) Nanoparticles: Efficient Nanocatalyst for the Hydrolysis of Ammonia-Borane at Room Temperature
(Mdpi Ag, 2015) Durap, Feyyaz; Caliskan, Salim; Ozkar, Saim; Karakas, Kadir; Zahmakiran, Mehmet
Intensive efforts have been devoted to the development of new materials for safe and efficient hydrogen storage. Among them, ammonia-borane appears to be a promising candidate due to its high gravimetric hydrogen storage capacity. Ammonia-borane can release hydrogen on hydrolysis in aqueous solution under mild conditions in the presence of a suitable catalyst. Herein, we report the synthesis of ruthenium(0) nanoparticles stabilized by dihydrogenphosphate anions with an average particle size of 2.9 +/- 0.9 nm acting as a water-dispersible nanocatalyst in the hydrolysis of ammonia-borane. They provide an initial turnover frequency (TOF) value of 80 min(-1) in hydrogen generation from the hydrolysis of ammonia-borane at room temperature. Moreover, the high stability of these ruthenium(0) nanoparticles makes them long-lived and reusable nanocatalysts for the hydrolysis of ammonia-borane. They provide 56,800 total turnovers and retain similar to 80% of their initial activity even at the fifth catalytic run in the hydrolysis of ammonia-borane at room temperature.
A Facile One-Step Synthesis of Polymer Supported Rhodium Nanoparticles in Organic Medium and Their Catalytic Performance in the Dehydrogenation of Ammonia-Borane
(Royal Soc Chemistry, 2012) Karahan, Senem; Zahmakiran, Mehmet; Ozkar, Saim
A new type of supported rhodium nanoparticles were reproducibly prepared from N2H4BH3 reduction of [Rh(mu-Cl)(1,5-cod)](2) without using any solid support and pre-treatment technique. Their characterization shows the formation of well dispersed rhodium(0) nanoparticles within the framework of a polyaminoborane based polymeric support. These new rhodium(0) nanoparticles were found to be the most active supported catalyst in the catalytic dehydrogenation of ammonia-borane in water at room temperature.
Hydrogen Generation From the Hydrolysis of Hydrazine-Borane Catalyzed by Rhodium(0) Nanoparticles Supported on Hydroxyapatite
(Pergamon-elsevier Science Ltd, 2012) Celik, Derya; Karahan, Senem; Zahmakiran, Mehmet; Ozkar, Saim
Herein, we report the preparation and characterization of rhodium(0) nanoparticles supported on hydroxyapatite (Ca-10(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 N-2 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) nanopaiticles 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. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Hydrogen Liberation From the Hydrolytic Dehydrogenation of Dimethylamine-Borane at Room Temperature by Using a Novel Ruthenium Nanocatalyst
(Royal Soc Chemistry, 2012) Caliskan, Salim; Zahmakiran, Mehmet; Durap, Feyyaz; Ozkar, Saim
Herein we report the discovery of an in situ generated, highly active nanocatalyst for the room temperature dehydrogenation of dimethylamine-borane in water. The new catalyst system consisting of ruthenium(0) nanoparticles stabilized by the hydrogenphosphate anion can readily and reproducibly be formed under in situ conditions from the dimethylamine-borane reduction of a ruthenium(III) precatalyst in tetrabutylammonium dihydrogenphosphate solution at 25 +/- 0.1 degrees C. These new water dispersible ruthenium nanoparticles were characterized by using a combination of advanced analytical techniques. The results show the formation of well-dispersed ruthenium(0) nanoparticles of 2.9 +/- 0.9 nm size stabilized by the hydrogenphosphate anion in aqueous solution. The resulting ruthenium(0) nanoparticles act as a highly active catalyst in the generation of 3.0 equiv. of H-2 from the hydrolytic dehydrogenation of dimethylamine-borane with an initial TOF value of 500 h(-1) at 25 +/- 0.1 degrees C. Moreover, they provide exceptional catalytic lifetime (TTO = 11 600) in the same reaction at room temperature. The work reported here also includes the following results; (i) monitoring the formation kinetics of the in situ generated ruthenium nanoparticles, by using the hydrogen generation from the hydrolytic dehydrogenation of dimethylamine-borane as a catalytic reporter reaction, shows that sigmoidal kinetics of catalyst formation and concomitant dehydrogenation fits well to the two-step, slow nucleation and then autocatalytic surface growth mechanism, A -> B (rate constant k(1)) and A + B -> 2B (rate constant k(2)), in which A is RuCl3 center dot 3H(2)O and B is the growing, catalytically active Ru(0)(n) nanoclusters. (ii) Hg(0) poisoning coupled with activity measurements after solution infiltration demonstrates that the in situ generated ruthenium(0) nanoparticles act as a kinetically competent heterogeneous catalyst in hydrogen generation from the hydrolytic dehydrogenation of dimethylamine-borane. (iii) A compilation of kinetic data depending on the temperature and catalyst concentration is used to determine the dependency of reaction rate on catalyst concentration and the activation energy of the reaction, respectively.
Hydroxyapatite-Nanosphere Supported Ruthenium(0) Nanoparticle Catalyst for Hydrogen Generation From Ammonia-Borane Solution: Kinetic Studies for Nanoparticle Formation and Hydrogen Evolution
(Royal Soc Chemistry, 2014) Durak, Halil; Gulcan, Mehmet; Zahmakiran, Mehmet; Ozkar, Saim; Kaya, Murat
The development of readily prepared effective heterogeneous catalysts for hydrogen generation from ammonia-borane (AB; NH3BH3) solution under mild conditions still remains a challenge in the field of "hydrogen economy". In this study, we report our finding of an in situ generated, highly active ruthenium nanocatalyst for the dehydrogenation of ammonia-borane in water at room temperature. The new catalyst system consists of ruthenium(0) nanoparticles supported on nanohydroxyapatite (RuNPs@nano-HAp), and can be reproducibly prepared under in situ conditions from the ammonia-borane reduction of Ru3+ ions exchanged into nanohydroxyapatite (Ru3+@nano-HAp) during the hydrolytic dehydrogenation of ammonia-borane at 25 +/- 0.1 degrees C. Nanohydroxyapatite-supported ruthenium(0) nanoparticles were characterized by a combination of advanced analytical techniques. The sum of their results shows the formation of well-dispersed ruthenium(0) nanoparticles with a mean diameter of 2.6 +/- 0.6 nm on the surface of the nanospheres of hydroxyapatite by keeping the host matrix intact. The resulting RuNPs@nano-HAp are highly active catalyst in the hydrolytic dehydrogenation of ammonia-borane with an initial TOF value of 205 min(-1) by generating 3.0 equiv. of H-2 per mole of ammonia-borane at 25 +/- 0.1 degrees C. Moreover, they are sufficiently stable to be isolated and bottled as solid materials, which can be reused as active catalyst under the identical conditions of first run. The work reported here also includes the following results: (i) monitoring the formation kinetics of the in situ generated RuNPs@nano-HAp by hydrogen generation from the hydrolytic dehydrogenation of ammonia-borane as the reporter reaction. The sigmoidal kinetics of catalyst formation and concomitant dehydrogenation fits well to the two-step, slow nucleation, followed by autocatalytic surface growth mechanism, P -> Q (rate constant k(1)) and P + Q -> 2Q (rate constant k(2)), in which P is Ru3+@nano-HAp and Q is the growing, catalytically active RuNPs@nano-HAp; (ii) the compilation of kinetic data for the RuNPs@nano-HAp catalyzed hydrolytic dehydrogenation of ammonia-borane depending on the temperature and catalyst concentration to determine the dependency of reaction rate on catalyst concentration and activation parameters (E-a, Delta H-#, and Delta S-#) of the reaction.
Iridium(O) Nanoparticles Dispersed in Zeolite Framework: a Highly Active and Long-Lived Green Nanocatalyst For-The Hydrogenation of Neat Aromatics at Room Temperature
(Elsevier, 2014) Tonbul, Yalcin; Zahmakiran, Mehmet; Ozkar, Saim
The complete hydrogenation of aromatic molecules is one of the key transformation employed in the synthetic and petroleum chemistry. Described herein is a new catalytic nanomaterial for the hydrogenation of neat aromatics under mild conditions. A novel nanocatalyst, consisting of iridium(O) nanoparticles stabilized by zeolite with EAU framework could reproducibly been prepared from the reduction of iridium(III)-exchanged zeolite in an aqueous sodium borohydride solution at room temperature and characterized by ICP-MS, P-XRD, HRTEM, XPS, N-2-Ads.-Des., and P(C6H11)(3) poisoning. The results reveal the formation of iridium(O) nanoparticles of 5.8 +/- 2.1 nm size dispersed on the external surface along with iridium(O) nanolclusters in cavities of zeolite-Y whereby the host matrix remains intact. The resulting iridium(O) nanoparticles were employed as heterogeneous catalyst in the hydrogenation of various aromatic substrates (benzene, toluene, o-xylene and mesitylene) in the solvent-free systems at room temperature and 3 bar initial Hy pressure. They are highly active catalyst in the hydrogenation of neat aromatics, such as they can completely hydrogenate benzene to cyclohexane with an initial turnover frequency value of TOE= 3215 h(-1). Moreover, they show high durability against to leaching and sintering throughout the catalytic runs, which make them reusable catalyst. More importantly, testing the catalytic lifetime of our iridium(O) nanoparticles showed that they provide previously unprecedented total turnover number of TO = 197,000 over 92 h before deactivation in the hydrogenation of benzene at room temperature and 3 bar initial H-2 pressure. (C) 2013 Elsevier B.V. All rights reserved.
Palladium(0) Nanoparticles Supported on Metal Organic Framework as Highly Active and Reusable Nanocatalyst in Dehydrogenation of Dimethylamine-Borane
(Elsevier Science Bv, 2014) Gulcan, Mehmet; Zahmakiran, Mehmet; Ozkar, Saim
Palladium(0) nanoparticles supported on the external surface of Cu-3(btc)(2) framework (PdNPs@Cu-3(btc)(2)) were in-situ generated from the reduction of Pd(acac)2 precursor impregnated on the Cu-3(btc)(2) support during the dehydrogenation of dimethylamine-borane in toluene at room temperature. The characterization of PdNPs@Cu-3(btc)(2) by using advanced analytical techniques shows the formation of well-dispersed palladium(0) nanoparticles supported on Cu-3(btc)(2) surface. These new palladium(0) nanoparticles were found to be the most active and the longest-lived nanocatalyst with superior reusability performance in the dehydrogenation of dimethylamine-borane at room temperature. (C) 2013 Elsevier B.V. All rights reserved.
Ruthenium(0) Nanoparticles Stabilized by Metal-Organic Framework (zif-8): Highly Efficient Catalyst for the Dehydrogenation of Dimethylamine-Borane and Transfer Hydrogenation of Unsaturated Hydrocarbons Using Dimethylamine-Borane as Hydrogen Source
(Elsevier Science Bv, 2014) Yurderi, Mehmet; Bulut, Ahmet; Zahmakiran, Mehmet; Gulcan, Mehmet; Ozkar, Saim
Ruthenium(0) nanoparticles supported on zeolitic imidazolate framework (ZIF-8), RuNPs/ZIF-8, were reproducibly prepared by borohydride reduction of RuCl3/ZIF-(8) precatalyst in water at room temperature. The characterization of the dehydrated RuNPs/ZIF-8 was done by a combination of complimentary techniques, which reveals that the formation of well-dispersed ruthenium(0) nanoparticles (1.9 +/- 0.6 nm) on the surface of ZIF-8 by keeping the host framework intact. The catalytic activity of RuNPs/ZIF-8 was firstly tested in the dehydrogenation of dimethylamine-borane ((CH3)(2)NHBH3) in toluene. We found that ruthenium(0) nanoparticles supported on ZIF-8 can catalyze the dehydrogenation of dimethylamineborane with an initial TOF value of 59 min(-1) at 40 degrees C. Additionally, RuNPs/ZIF-8 catalyze the transfer hydrogenation of various unsaturated substrates in the presence of dimethylamine borane as hydrogen source even at low catalyst loadings. More importantly, they show high durability against leaching and sintering throughout the catalytic runs, which make them reusable catalyst in these important catalytic transformations. (C) 2014 Elsevier B.V. All rights reserved.
Size-Controllable Apts Stabilized Ruthenium(0) Nanoparticles Catalyst for the Dehydrogenation of Dimethylamine-Borane at Room Temperature
(Royal Soc Chemistry, 2012) Zahmakiran, Mehmet; Philippot, Karine; Ozkar, Saim; Chaudret, Bruno
Dimethylamine-borane, (CH3)(2)NHBH3, has been considered as one of the attractive materials for the efficient storage of hydrogen, which is still one of the key issues in the "Hydrogen Economy". In a recent communication we have reported the synthesis and characterization of 3-aminopropyltriethoxysilane stabilized ruthenium(0) nanoparticles with the preliminary results for their catalytic performance in the dehydrogenation of dimethylamine-borane at room temperature. Herein, we report a complete work including (i) effect of initial [APTS]/[Ru] molar ratio on both the size and the catalytic activity of ruthenium(0) nanoparticles, (ii) collection of extensive kinetic data under non-MTL conditions depending on the substrate and catalyst concentrations to define the rate law of Ru(0)/APTS-catalyzed dehydrogenation of dimethylamine-borane at room temperature, (iii) determination of activation parameters (E-a, Delta H# and Delta S#) for Ru(0)/APTS-catalyzed dehydrogenation of dimethylamine-borane; (iv) demonstration of the catalytic lifetime of Ru(0)/APTS nanoparticles in the dehydrogenation of dimethylamine-borane at room temperature, (v) testing the bottlability and reusability of Ru(0)/APTS nanocatalyst in the room-temperature dehydrogenation of dimethylamine-borane, (vi) quantitative carbon disulfide (CS2) poisoning experiments to find a corrected TTO and TOF values on a per-active-ruthenium-atom basis, (vii) a summary of extensive literature review for the catalysts tested in the catalytic dehydrogenation of dimethylamine-borane as part of the results and discussions.
Transition Metal Nanoparticles in Catalysis for the Hydrogen Generation From the Hydrolysis of Ammonia-Borane
(Springer/plenum Publishers, 2013) Zahmakiran, Mehmet; Ozkar, Saim
Over the last decade, transition metal nanoparticles have attracted much attention owing to their unique properties, different to their bulk counterparts, which facilitate their application in different fields from materials science to engineering. Of particular interest, the use of transition metal nanoparticles in catalysis has brought transcendent efficiency in terms of activity, selectivity and lifetime to heterogeneous catalysis. In this account, we summarize the recent developments in the synthesis routes and the catalytic performance of transition metal nanoparticles tested in the hydrogen generation from the hydrolysis of ammonia-borane, which has been considered as one of the attractive materials for the efficient storage of hydrogen that is still one of the key issues in the "Hydrogen Economy".