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    A general approach to halloysite clay mineral
    (Nova Science Publishers, Inc., 2020) Karaismailoğlu, Meltem; Kutlu, Sena Zeynep; Demir, T. U.
    Halloysite is a natural clay mineral that belongs to the kaolin group. Its chemical formula is Al2(OH)4Si2O5.nH2O. When n is equal to 2, it is hydrated, and when n is equal to 0, the halloysite is dehydrated. Generally, halloysite has a tubular structure; however, as a result of different deposits and crystallization conditions, this mineral can consist of spheroidal and plate-like particles. Its main deposits are in the United States, China, New Zealand, Mexico, Brazil, and Turkey where halloysite is formed by weathering or hydrothermal alteration of pumice, ultramafic, and volcanic rocks. Halloysite can be used in various fields due to its characteristic features. Primarily, this mineral is an ideal nanofiller for polymer composites. It is also utilized in the manufacture of ceramic wares and encapsulation of drugs in the pharmaceutical industry. Moreover, its higher specific surface area makes halloysite a good candidate for catalyst support. © 2020 Nova Science Publishers, Inc. All rights reserved.
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    Hydrogen production by catalytic methane decomposition over yttria doped nickel based catalysts
    (Pergamon-Elsevier Science Ltd, 2019) Karaismailoğlu, Meltem; Figen, Halit Eren; Baykara, Sema Zeynep
    Catalytic methane decomposition can become a green process for hydrogen production. In the present study, yttria doped nickel based catalysts were investigated for catalytic thermal decomposition of methane. All catalysts were prepared by sol-gel citrate method and structurally characterized with X-ray powder diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Brunauer, Emmet and Teller (BET) surface analysis techniques. Activity tests of synthesized catalysts were performed in a tubular reactor at 500 ml/min total flow rate and in a temperature range between 390 degrees C and 845 degrees C. In the non-catalytic reaction, decomposition of methane did not start until 880 degrees C was reached. In the presence of the catalyst with higher nickel content, methane conversion of 14% was achieved at the temperature of 500 degrees C. Increasing the reaction temperature led to higher coke formation. Lower nickel content in the catalyst reduced the carbon formation. Consequently, with this type of catalyst methane conversion of 50% has been realized at the temperature of 800 degrees C. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Methane decomposition over Fe-based catalysts
    (Elsevier Ltd, 2020) Karaismailoğlu, Meltem; Figen, Halit Eren; Baykara, Sema Z.
    Catalytic approach for methane decomposition can be seriously considered as a promising process for COx free hydrogen generation. In this study, catalytic methane decomposition was performed using Fe-based catalysts, and catalytic performance tests were carried out in a CH4:N2 flow at 750 and 800 °C. The analyses of reaction products were carried out by a mass spectrometer. For the preparation of Fe-based catalysts, sol-gel method was utilized. Yttria (Y2O3) and alumina (Al2O3) were used as support materials. Theoretical molar ratios (Fe2O3/Y2O3/Al2O3) of the samples C1–C5 were 1:0:0, 1:1:0, 1:1:5, 2:1:4 and 3:1:6, respectively. The characterization analyses of fresh and spent catalysts were performed with XRD, SEM, TPR, TG-FTIR and BET surface analysis techniques. Surface basicity of catalysts was determined via CO2-TPD measurements. In the presence of Fe2O3/Y2O3 and Fe2O3/Y2O3/Al2O3 catalysts, methane conversions of 29% and 4% were achieved at 750 °C. Adding alumina into Fe2O3/Y2O3 catalyst leads to the formation of garnet type crystal structure which reduces catalytic activity. © 2020 Hydrogen Energy Publications LLC
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    Molybdenum- and vanadium-containing perovskite electrocatalysts for dissociation of H2S
    (Wiley, 2020) Karaismailoğlu, Meltem; Güldal, Nafi Özgür; Figen, Halit Eren; Baykara, Sema Zeynep
    Catalytic operations, achieving considerable energy savings, continue getting wider application especially in clean energy systems. Perovskite materials, owing to their chemical and thermal stability, can be conveniently used as catalysts and electrode materials at wide temperature ranges. Hydrogen sulfide (H2S) offers a new and abundant source of hydrogen, the ultimate energy carrier. In the present work, change in electrical conductivity of catalysts obtained by adding molybdenum (Mo) and vanadium (V) as B to the perovskite structure with lanthanum (La) and strontium (Sr) as A and A ', respectively, has been studied within a temperature range of up to 1100 K. Samples La0.75Sr0.25MoO3 and LaSr0.5V0.5O3 demonstrated the highest values of conductivity at 1100 K. At lower temperatures, Cr-added Mo and V catalysts La0.9Sr0.1Cr0.5Mo0.5O3 and La0.9Sr0.1Cr0.5V0.5O3 had higher conductivity, closely followed by LaSr0.5V0.5O3.