Yazar "Zahmakiran, Mehmet" seçeneğine göre listele

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    Amine-functionalized graphene nanosheet-supported PdAuNi alloy nanoparticles: efficient nanocatalyst for formic acid dehydrogenation
    (Royal Soc Chemistry, 2018) Bulut, Ahmet; Yurderi, Mehmet; Kaya, Murat; Aydemir, Murat; Baysal, Akin; Durap, Feyyaz; Zahmakiran, Mehmet
    Formic acid (HCOOH), a major by-product of biomass processing with high energy density, stability and non-toxicity, has a great potential as a safe and a convenient liquid hydrogen (H-2) storage material for combustion engines and fuel cell applications. However, high-purity hydrogen release from the catalytic decomposition of aqueous formic acid solution at desirable rates under mild conditions stands as a major challenge that needs to be solved for the practical use of formic acid in on-demand hydrogen generation systems. Described herein is a new nanocatalyst system comprised of 3-aminopropyltriethoxysilane-functionalized graphene nanosheet-supported PdAuNi alloy nanoparticles (PdAuNi/f-GNS), which can reproducibly be prepared by following double solvent method combined with liquid-phase chemical reduction, all at room temperature. PdAuNi/f-GNS selectively catalyzes the decomposition of aqueous formic acid through the dehydrogenation pathway (similar to 100% H-2 selectivity), in the absence of any promoting additives (alkali formates, Bronsted bases, Lewis bases, etc.). PdAuNi/f-GNS nanocatalyst provides CO-free H-2 generation with a turnover frequency of 1090 mol H-2 mol metal(-1) h(-1) in the additive-free dehydrogenation of formic acid at almost complete conversion (>= 92%) even at room temperature. The catalytic activity provided by PdAuNi/f-GNS nanocatalyst is higher than those obtained with the heterogeneous catalysts reported to date for the additive-free dehydrogenation of formic acid. Moreover, PdAuNi/f-GNS nanoparticles show high durability against sintering, clumping and leaching throughout the catalytic runs, so that the PdAuNi/f-GNS nanocatalyst retains almost its inherent catalytic activity and selectivity at the end of the 10th recycle.
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    Cobalt nanoparticles supported on alumina nanofibers (Co/Al2O3): Cost effective catalytic system for the hydrolysis of methylamine borane
    (Pergamon-Elsevier Science Ltd, 2019) Baguc, Ismail Burak; Yurderi, Mehmet; Bulut, Ahmet; Celebi, Metin; Kanberoglu, Gulsah Saydan; Zahmakiran, Mehmet; Kaya, Murat
    Amongst different amine-borane derivatives, methylamine-borane (CH3NH2BH3) seems to be one of the capable aspirants in the storing of hydrogen attributable to its high hydrogen capacity, stability and aptitude to generate hydrogen through its catalytic hydrolysis reaction under ambient conditions. In this research paper, we report that cobalt nano-particles supported on alumina nanofibers (Co/Al2O3) are acting as active nanocatalyst for catalytic hydrolysis of methylamine-borane. Co/Al2O3 nanocatalyst was fabricated by double-solvent method followed with wet-chemical reduction, and was characterized by utilizing various spectroscopic methods and imaging techniques. The results gathered from these analyses showed that the formation Al2O3 nanofibers supported cobalt(0) nanoparticles with a mean diameter of 3.9 +/- 1.2 nm. The catalytic feat of these cobalt nanoparticles was scrutinized in the catalytic hydrolysis of methylamine-borane by considering their activity and durability performances. They achieve releasing of 3.0 equivalent of H-2 via methylamine-borane hydrolysis at room temperature (initial TOF = 297 mol H-2/mol metal x h). Along with activity the catalytic durability of Co/Al2O3 was also studied by carrying out recyclability tests and it was found that these supported cobalt nanoparticles have good durability during the course of the catalytic recycles so that Co/Al2O3 preserves almost its innate activity at 5th catalytic recycle. The studies presented here also contains kinetic investigation of Co/Al2O3 catalyzed methylamine borane hydrolysis depending on the temperature, cobalt and methylamine borane concentrations, which were used to define rate expression and the activation energy of the catalytic reaction. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    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.
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    Highly active Pd nanoparticles decorated on benzene-ring doped g-C3N4 as catalyst in methylene Blue degradation and Cr (VI) ions reduction
    (Wiley, 2024) Önal, Halil İbrahim; Durap, Feyyaz; Aydemir, Murat; Zahmakiran, Mehmet
    The development of simply prepared, highly active and reusable nanocatalysts for methylene blue degradation (MB) or Cr (VI) ions reduction under sunlight conditions in wastewater remains a challenge in the field of green chemistry. Addressed herein is the catalyst of Pd(0) nanoparticles supported on benzene ring doped graphitic carbon nitride (Pd@BD-g-C3N4) for MB degradation or Cr (VI) ions reduction under visible light irradiation. Pd@BD-g-C3N4 nanocatalyst has been synthesized using the facile wet impregnation-chemical reduction method to boost the catalytic efficiency of BD-g-C3N4. The MB degradation or Cr (VI) ions reduction proceeded efficiently in the presence of Pd@BD-g-C3N4. Compared with pure BD-g-C3N4 in both studies, the hybrid photocatalyst Pd@BD-g-C3N4-exhibited enhanced visible light photoactivity was higher than of pure BD-g-C3N4. In addition, in the reusability tests, it was observed that the Pd@BD-g-C3N4 photocatalyst has good stability and repeated cycle performance. The electronic and morphologic structure of support material and nanocatalyst were characterized by several techniques such as FT-IR, DR/UV-Vis, BET, SEM-EDX, HR-TEM, P-XRD, and XPS analyses.
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    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.
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    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.
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    Palladium nanoparticles supported on hydroxyapatite nanospheres: Highly active, reusable and green catalyst for Suzuki - Miyaura cross coupling reactions under aerobic conditions
    (Wiley-V C H Verlag Gmbh, 2018) Bulut, Ahmet; Aydemir, Murat; Durap, Feyyaz; Gülcan, Mehmet; Zahmakiran, Mehmet
    The development of simply prepared, highly active and reusable nanocatalysts for Suzuki-Miyaura cross coupling reactions under mild and green conditions remains a challenge in the field of synthetic organic chemistry. Herein, we describe a new nanocatalyst comprising of palladium nanoparticles supported on hydroxyapatite nanospheres, which can reproducibly be formed in-situ during the Suzuki-Miyaura coupling reactions starting with Pd(II)-exchanged nanohydroxyapatite. The characterization of the resulting catalyst by using ICP-OES, P-XRD, XPS, TEM, HRTEM, SEM and N-2-adsorption-desorption analyses revealed that the formation of 3.7 +/- 1.3nm palladium(0) nanoparticles (Pd(0)(similar to 430) nanoclusters) on the surface of nano-sized (similar to 50nm) hydroxyapatite (nano-HAp) support by keeping the host framework intact. This previously unappreciated combination of Pd NPs and nano-HAp (PdNPs@nano-HAp) shows excellent activities (TOF's > 3x10(5) h(-1)) in the Suzuki-Miyaura cross coupling reactions of different arylbromides with phenylboronic acid under mild, green and aerobic conditions. More importanly, these new supported palladium(0) nanoparticles were found to be highly durable nanocatalyst throughout the reusability experiments, they maintain almost their inherent activity after 10(th) catalytic cycle at high conversion (> 98%).