Browsing by Author "Karakas, Kadir"

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The Catalytic Activity of Halloysite-Supported Ru Nanoparticles in the Methanolysis of Sodium Borohydride for Hydrogen Production
(Pergamon-elsevier Science Ltd, 2023) Gozeten, Ibrahim; Karakas, Kadir; Karatas, Yasar; Tunc, Mehmet; Gulcan, Mehmet
Finding environmentally friendly new energy sources is very urgent for a sustainable and clean energy future. It is vital to reach clean energy sources such as hydrogen, which does not create a polluting by-product when burned with oxygen. In this study, for a livable clean universe, hydrogen production studies were carried out from sodium borohydride (NaBH4), which is a very good hydrogen storage material, in a methanolysis environment, over ruthenium nanoparticles (Ru (0) NPs) impregnated on halloysite (Hall) support ma-terial (Ru (0)@Hall) at room conditions. The catalytic performance of the newly synthesized Ru (0)@Hall nanocatalyst was tested in the NaBH4 methanolysis reaction for hydrogen production. It was determined that Ru (0)/Hall nanocatalyst showed excellent activity (initial turn-over frequency (TOFinitial) = 1882 h-1; 31.37 min-1) and reusability (at the end of the 5th cycle, it retained 90% of its initial activity) performance in the catalytic meth-anolysis of NaBH4. The analyzes of the Ru (0)@Hall nanocatalyst, both fresh and at the end of the 5th catalytic cycle, were made with advanced analytical methods (ICP-OES, XRD, XPS, SEM, HRTEM, TEM, TEM-EDX, BET) and the nature of the catalytic material was clarified. The results showed the homogeneous distribution of Ru (0) NPs on the Hall surface (mean size = 1.53 +/- 0.17 nm). Kinetic studies of hydrogen production from catalytic methanolysis reaction of NaBH4 were performed based on nanocatalyst [Ru (0)@Hall], substrate [NaBH4] concentrations, and temperature (298-318 K). From the kinetic data, the kinetic parameters (Ea, DH*, and DS*) were calculated and the rate equation was determined.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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.
Nanohydrotalcite Supported Ruthenium Nanoparticles: Highly Efficient Heterogeneous Catalyst for the Oxidative Valorization of Lignin Model Compounds
(Wiley-v C H verlag Gmbh, 2017) Baguc, Ismail Burak; Celebi, Metin; Karakas, Kadir; Ertas, Ilknur Efecan; Keles, Muhammed Nuri; Kaya, Murat; Zahmakiran, Mehmet
The catalytic transformation of lignocellulosic biomass derived chemicals into value-added chemicals under mild conditions remains a challenge in the fields of synthetic chemistry and catalysis. Herein, we describe a new heterogeneous catalyst system that efficiently works in the oxidative valorization of lignin model compounds. This new heterogeneous catalyst system comprised of nano-sized hydrotalcite (n-HT; Mg6Al2 (CO3)(OH)(16)) supported ruthenium(0) nanoparticles (Ru/ n-HT) was prepared by ion-exchange of [Ru(OH2)Cl-5](2-) anions with the extraframework CO32- anions of n-HT followed by their borohydride reduction (NaBH4) in water at room temperature. The characterization of Ru/n-HT was done by the combination of various spectroscopic and the sum of their results revealed that the formation of well-dispersed ruthenium(0) nanoparticles with a mean diameter of 3.2 +/- 0.9 nm on the surface of n-HT structure. The catalytic performance of Ru/n-HT in terms of activity, selectivity and stability was tested in the aerobic oxidation of cinnamyl, veratryl and vanillyl alcohols, which are important lignin model compounds used to mimic the propyl side chain, the phenolic and non-phenolic, respectively functional groups of lignin. We found that Ru/ n-HT nanocatalyst displays remarkable activity at high selectivity and almost complete conversion in these catalytic transformations under mild reaction conditions (at 373 K under 3 bar initial O-2 pressure).
Nickel Nanoparticles Decorated on Electrospun Polycaprolactone/Chitosan Nanofibers as Flexible, Highly Active and Reusable Nanocatalyst in the Reduction of Nitrophenols Under Mild Conditions
(Elsevier Science Bv, 2017) Karakas, Kadir; Celebioglu, Asli; Celebi, Metin; Uyar, Tamer; Zahmakiran, Mehmet
Today, the reduction of nitro aromatics stands a major challenge because of the pollutant and detrimental nature of these compounds. In the present study, we show that nickel(0) nanoparticles (Ni-NP) decorated on electrospun polymeric (polycaprolactone(PCL)/chitosan) nanofibers (Ni-NP/ENF) effectively catalyze the reduction of various nitrophenols (2-nitrophenol, 2,4-dinitrophenol, 2,4,6-trinitrophenol) under mild conditions. Ni-NP/ENF nanocatalyst was reproducibly prepared by deposition-reduction technique. The detailed characterization of these Ni-NP/ENF based nanocatalyst have been performed by using various spectroscopic tools including ICP-OES, P-XRD, XPS, SEM, BFTEM, HRTEM and BFTEM-EDX techniques. The results revealed the formation of well-dispersed nickel(0) NP (d(mean) = 2.71-2.93 nm) on the surface of electrospun polymeric nanofibers. The catalytic activity of the resulting Ni-NP/ENF was evaluated in the catalytic reduction of nitrophenols in aqueous solution in the presence of sodium borohydride (NaBH4) as reducing agent, in which Ni-NP/ENF nanocatalyst has shown high activity (TOF=46.2 mol 2-nitrophenol/mol Ni min; 48.2 mol 2,4-dinitrophenol/mol Ni min; 65.6 mol 2,4,6-trinitrophenol/mol Ni min). More importantly, due to the nanofibrous polymeric support, Ni-NP/ENF has shown a flexible characteristics along with reusability property. Testing the catalytic stability of Ni-NP/ENF revealed that this new catalytic material provides high reusability performance (at 3rd reuse 86% for 2-nitrophenol, 83% 2,4-dinitrophenol and 82% 2,4,6-trinitrophenol) for the reduction of nitrophenols even at room temperature and under air. The present study reported here also includes the compilation of wealthy kinetic data for Ni-NP/ENF catalyzed the reduction of nitrophenols in aqueous sodium borohydride solution depending on temperature and type of support material (Al2O3, C, SiO2) to understand the effect of the support material and determine the activation parameters. (C) 2016 Elsevier B.V. All rights reserved.
Palladium Nanoparticles Decorated Graphene Oxide: Active and Reusable Nanocatalyst for the Catalytic Reduction of Hexavalent Chromium(Vi)
(Wiley-v C H verlag Gmbh, 2017) Celebi, Metin; Karakas, Kadir; Ertas, Ilknur Efecan; Kaya, Murat; Zahmakiran, Mehmet
Today, the catalytic reduction of Cr(VI) to Cr(III) stands one of the most important challenges in the environmental chemistry and catalysis due to highly stable, contaminant and toxic nature of Cr(VI). In this study, we show that a new nanocatalyst system comprised of 3-aminopropyltriethoxysilane (APTS) stabilized palladium(0) nanoparticles grafted onto the surface of graphene oxide (Pd/GO) efficiently works in the catalytic reduction of Cr(VI) to Cr(III) under mild reaction conditions. Pd/GO nanocatalyst was reproducibly prepared through two-steps procedure: (i) H-2 reduction of Pd(dba)2(dba= dibenzylideneacetone) in the presence of APTS in THF to synthesize colloidal APTS stabilized palladium(0) nanoparticles and then (ii) the deposition of 3-aminopropyltriethoxysilane stabilized palladium 0) nanoparticles onto the surface of graphene oxide (GO) by impregnation. The characterization of Pd/GO was carried out by advanced analytical techniques. The summation of the results acquired from these analyses reveals that the formation of well-dispersed and highly crystalline palladium(0) nanoparticles on the surface of GO. The catalytic performance of the resulting Pd/GO in terms of activity and stability was assessed in the catalytic reduction of Cr(VI) to Cr(III) in aqueous solution in the presence of formic acid (HCOOH) as a reducing agent. We found that Pd/GO nanocatalyst exhibits high activity (TOF= 3.6 mol Cr2O72-/mol Pdxmin) and reusability (> 90% at 5th reuse) in this catalytic transformation at room temperature.