Yazar "Bulut, Ahmet" seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • [ X ]
    Öğe
    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.
  • Küçük Resim
    Öğe
    Bimetallic PdxNi1-x and PdxCo1-x nanoparticles supported on K-OMS-2: Highly active, environmentally friendly and reusable nanocatalysts for the Suzuki–Miyaura cross-coupling reactions in water
    (Wiley, 2021) Durap, Feyyaz; Gülen, Yasemin; Abay, Ayşe; Bulut, Ahmet; Yurderi, Mehmet; Aydemir, Murat; Baysal, Akın; 0000-0003-0899-1948; 0000-0002-5520-0558; 0000-0001-5472-4213; 0000-0002-1697-8623; 0000-0002-0233-8940; 0000-0002-4238-5012; 0000-0001-7294-6792; 0000-0002-5633-3811
    Addressed herein is the catalysis of bimetallic PdxNi1-x and PdxCo1-x nanoparticles (NPs) supported on a cryptomelane-type manganese oxide (K-OMS-2) solid for the Suzuki-Miyaura cross-couplings of phenylboronic acid with various aryl halides. Bimetallic PdxNi1-x and PdxCo1-x NPs were prepared by using a conventional one-step impregnation-reduction method. Among these catalysts with different compositions of Ni and Pd or Co and Pd, the Pd0.2Ni0.8 and Pd0.2Co0.8 catalysts showed the highest activity in the Suzuki-Miyaura cross-couplings of various aryl halides including iodides, bromides, and even chlorides with phenylboronic acid in ambient air and water under reflux conditions. The Suzuki-Miyaura cross-coupling reaction proceeded efficiently in the presence of Pd0.2Ni0.8@K-OMS-2 and Pd0.2Co0.8@K-OMS-2 NPs under the optimized conditions in water. Pd0.2Ni0.8@K-OMS-2 and Pd0.2Co0.8@K-OMS-2 NPs provided high conversions up to 98% and 99% and turnover frequencies of 11,760 and 11,880 h(-1) in the cross-coupling of phenylboronic acid with 1-bromo-4-nitrobenzene. More importantly, these new supported Pd0.2Ni0.8@K-OMS-2 and Pd0.2Co0.8@K-OMS-2 NPs were found to be highly durable nanocatalyst throughout the reusability experiments, and they maintain almost their inherent activity after 10th and 5th catalytic cycle, respectively. Bimetallic Pd0.2Ni0.8@K-OMS-2 and Pd0.2Co0.8@K-OMS-2 NPs were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ICAPQ inductively coupled plasma mass spectroscopy (ICP-MS) analyses.
  • [ X ]
    Öğe
    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.
  • Küçük Resim
    Öğe
  • [ X ]
    Öğe
    Kranial pediküllü dorsal sıçan flebinde alfa tokoferolün distal flep nekrozuna etkisi: Deneysel çalışma
    (1999) Uzunlar, Ali Kemal; Yılmaz, Fahri; Gezici, Ayten; Yağmur, Yusuf; Arıncı, Atilla; Bulut, Ahmet
    Literatürde, güvenle hazırlanabilecek flep uzunluğunu artırmaya yönelik çeşitli farmakolojik ajanlarla yapılmış birçok çalışma vardır. Çalışmamız sıçanlarda kranial pediküllü random pattern bir flep modeli olan Mc Farlane flebi üzerinde yapıldı. Toplam 50 adet sıçan 25'i kontrol, 25'i de deney grubu olmak üzere iki eşit gruba ayrıldı. Kontrol grubundaki sıçanlara, plasebo amacıyla preoperatif 1. saatte ve postoperatif 1. günden itibaren izotonik NaCl subkütan olarak, deney grubundaki sıçanlara ise preoperatif 1. saatte alfa tokoferol intramüsküler olarak . verildi. Uygulamaya 10 gün süre ile devam edildi. Kontrol grubundaki fleplerde postoperatif 5. günde ortalama % 41.1, 10. günde % 49.16 oranında nekroz görülürken; E vitamini verilen grupta postoperatif 5. günde % 12.4, 10. günde ise % 15.44 oranında nekroz saptandı. Histopatolojik ve sintigrafik sonuçlar bu oranları destekler nitelikteydi. Sonuç olarak; E vitamininin antioksidan özelliği ile flep viabilitesini artırdığını gözlemledik.
  • Küçük Resim
    Öğe
    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%).