Browsing by Author "Tunc, Mehmet"

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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.
Dissolution Kinetics of Ulexite in Phosphoric Acid
(Asian Journal of Chemistry, 2008) Tunc, Mehmet
In present study, the dissolution kinetics of ulexite in phosphoric acid was-studied. The effects on the dissolution rate of particle size, temperature, acid concentration, solid-to-liquid ratio and stirring speed were experimentally investigated. It was determined that the dissolution rate increased with decreasing particle size and solid-to-liquid ratio and increasing reaction temperature. For acid concentrations up to 1 mol L-1, dissolution rate increased with increasing acid concentration. For higher acid concentrations, the dissolution rate was decreased as acid concentration increased. No effect of stirring speed on the dissolution rate was observed. The dissolution kinetics of ulexite was examined taking into consideration the heterogeneous and homogeneous reaction models. The tests carried out by graphical and statistical methods were showed that the following models with chemical reaction control for two different concentration levels was best fitted to the experimental data. 1-(1-X)(1/3) = [0.164.(D-1.44C0.92) (S/L)(-1.41e-34.196/RT)].t + 0.166 for C <= 1.M 1-(1-X)(1/3) = [0.152.D-1.48C-1.32 (S/L)(-1.42e-34.196/RT)].t + 0.176 for 1.0 M <= C.
Dissolution of Colemanite in (Nh4)2so4 Solutions
(Korean institute Chemical Engineers, 2007) Tunc, Mehmet; Kocakerim, Mehmet Muhtar; Kucuk, Ozkan; Aluz, Mehmet
Turkey is the country having the richest boron ores in the world, and colemanite, tincal and ulexite are the ores being mined mostly in Turkey. These ores are used in the production of various boron compounds of which the production methods are generally patented. Colemanite ore also is reacted with sulfuric acid to product boric acid. Produced by this method, boric acid contains various impurities which reduce the market value and are difficult to remove. This study investigated the reaction between colemanite and ammonium sulfate as an alternative method to produce boric acid. Particle size, ammonium sulfate concentration, solid to liquid ratio and reaction temperature were chosen as parameters. In results, the conversion rate was increased by decreasing particle size and solid to liquid ratio, by increasing ammonium sulfate concentration and temperature. A semi-empirical model with 40.46 kJmol(-1) activation energy representing this process was found as follows: 1-(1-X)(1/3) =2.12 x 10(2) (.) C-1.38 (.) R-0.75 (.) (S/L)(0.44) (.) e(-4866/T .) t(0.61).
Palladium Nanoparticles Supported on Activated Carbon (C) for the Catalytic Hexavalent Chromium Reduction
(Springer int Publ Ag, 2022) Gozeten, Ibrahim; Tunc, Mehmet
Hexavalent chromium is widely used in industry and causes human health and environmental problems due to its extremely toxic properties. On the contrary, trivalent chromium is necessary for living ecosystems. Therefore, reducing hexavalent chromium to trivalent chromium is the best strategy for detoxifying hexavalent chromium. Pd(0)@C nanocatalyst was prepared by a simple impregnationreduction method in solution under mild conditions at 298 K and was identified by XPS, XRD, TEM, TEM-EDX, HR-TEM, and ICP-OES analyses. TEM results showed that very well-dispersed Pd nanoparticles were formed on the C surface (mean particle sizes 3.98 +/- 0.24 nm). The catalytic performance of Pd(0)NPs impregnated on cheap and easily available commercial activated carbon were tested as heterogeneous nanocatalysts in the catalytic reduction of hexavalent chromium in the medium of formic acid, which is a good reducing agent, and sodium formate as the promoter at 298 K. It was determined that the formed Pd(0) nanoclusters could successfully reduce Cr(VI) to Cr(III) with high selectivity (similar to 97%) in formic acid and sodium formate solution under mild conditions. It was also observed that the Pd(0)@C catalyst retained a significant (>75%) initial activity even after the 5th use. In addition, the kinetic studies of the catalytic reduction reaction of Cr(VI) catalyzed by Pd(0)@C nanoparticles were investigated depending on the substrate [Cr2O72-], catalyst [Pd(0)@C], sodium formate [HCOONa], formic acid [HCOOH] concentrations, and temperature parameter. From the rich kinetic data obtained, the nature of the velocity equation was explained, and the activation parameters were calculated.
Palladium Nanoparticles Supported on Aluminum Oxide (Al2o3) for the Catalytic Hexavalent Chromium Reduction
(Springer, 2022) Gozeten, Ibrahim; Tunc, Mehmet
While Cr(VI), a hazardous industrial waste, is an acute toxic, carcinogenic, and proven mutagenic pollutant, Cr(III) is thought to be an essential element for living things. In this study, Pd(0)@ Al2O3 nanoclusters supported on Al2O3 were reproducibly prepared in aqueous solution at 25 degrees C by a simple impregnation-reduction method. The results showed that Pd(0)@Al2O3 nanoclusters with average particle size of 3.01 +/- 0.19 nm were formed, well dispersed over the Al2O3 surface. The Al2O3-supported Pd(0)@Al2O3 nanoclusters were used as heterogeneous nanocatalysts in the catalytic reduction of Cr(VI) in formic acid medium, which is a good reducing agent under mild conditions. It has been observed that catalyst Pd(0)@Al2O3 can catalyze the catalytic reduction of Cr(VI) with high selectivity (- %99) and efficiency (TOF) (138 mol Cr2O72-/ mol Pd min.). More importantly, the exceptional stability of the Pd(0)@Al2O3 nanocatalyst against flocculation, leaching, and CO poisoning showed that this catalyst is a reusable catalytic material in the catalytic reduction reaction of Cr(VI). It was observed that the Pd(0)@Al2O3 catalyst maintained a significant (> 84%) initial TOF value even after the 5th use. The Pd(0)@Al2O3 nanocatalyst was identified by advanced analytical methods (XPS, XRD, TEM, TEM-EDX, HR-TEM, ICP-OES). In addition, for the kinetic data of the catalytic reduction reaction of Cr(VI) catalyzed by Pd(0)@Al2O3, the rate equation and Ea, Delta H-#, and Delta S-# activation parameters were derived depending on the [catalyst], [Cr2O72-], [HCOOH], and [HCOONa] concentrations and temperature.
Palladium Nanoparticles Supported on Multi-Walled Carbon Nanotube (Mwcnt) for the Catalytic Hexavalent Chromium Reduction
(Elsevier Science Sa, 2022) GOzeten, Ibrahim; Tunc, Mehmet
Chromium (VI) is widely accepted as an acute toxic contaminant in living ecosystems, while the trivalent Chromium form (III) is thought to be an important element for living beings. This study showed that zero palladium (Pd-0) metal nanoparticles supported onto a multi-walled carbon nanotube (MWCNT) catalyst (Pd@MWCNT) effectively catalyzed the reduction reaction of Chromium (VI) to Chromium (III) using HCOOH (formic acid) as a reducing agent. The catalyst (Pd@MWCNT) was prepared reproducibly in the aqueous mixture at room conditions through the impregnation-reduction technique and identified using some analytical characterization techniques (HRTEM, DR/UV-vis, TEM-EDX, TEM, XPS, ICP-OES, and P-XRD). The results of the characterization studies show that the palladium(0) nanoparticles (demean = 2.20 +/- 0.25 nm) are very well dispersed onto the MWCNT support material surface. The stability and activity of catalytic performance of Pd(0) metal nanoparticles were investigated in the reactions of Chromium (VI) to Chromium (III) in HCOOH solution. The results show that the Pd@MWCNT catalyst exhibited excellent activity (TOF = 281 mol Cr2O72-/mol Pd min), even after 5 times of reuse (<86%) in the reduction reaction of Chromium (VI) to Chromium (III) at 298K. In addition, this study includes very rich kinetic data depending on [Pd@MWCNT], [HCOOH], [HCOONa], [Cr2O72-] concentrations and temperature parameters to determine the nature of the reduction rate and activation parameters of Cr(VI) catalyzed by Pd@MWCNT nanocatalyst in the formic acid medium as a reducing agent.
Pyrolysis of Black Cumin Seed: Significance of Catalyst and Temperature Product Yields and Chromatographic Characterization
(Taylor & Francis inc, 2019) Durak, Halil; Genel, Salih; Tunc, Mehmet
In this study, black cumin seed cake was transformed into liquid and solid products via pyrolysis method at 300, 400 and 500 degrees C with Ca(OH)(2), Al2O3, SnCl4.5H(2)O catalysts and without catalyst. The obtained liquid and solid products were examined with GC-MS, Elemental, FT-IR, H-1 NMR and SEM analysis methods. The highest liquid product yield was obtained as 30% in the presence of Al2O3 catalyst. All catalysts were found to be effective on conversion. According to the results of the elemental analysis of the liquid products obtained at the end of the experiments, HHV values were found between 32.44 and 36.19 Mj/kg. According to the results of GC-MS analysis of the liquid products, in total, 77, 61 and 66 pieces of compounds consist of monoaromatics, aliphatics, oxygenated compounds with different properties were obtained at 300, 400 and 500 degrees C reaction temperatures respectively. The results of the FT-IR and H-1 NMR that are used to examine the liquid products support the results of GC-MS. [GRAPHICS] .