Yazar "Onal, Isik" seçeneğine göre listele

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    Density functional theory investigation of acetylene dehydrogenation on metal exchanged ZSM-5 clusters for initial step of carbon nanotube production
    (Elsevier Science Bv, 2013) Tezsevin, Ilker; Fellah, Mehmet Ferdi; Onal, Isik
    Adsorption and dehydrogenation of acetylene have been theoretically studied on [M(SiH3)(4)AlO4] and [(M-(mu-O)-M)Si6Al2O9H14] (where M = Co, Fe, Ni, and V) clusters representing ZSM-5 zeolite. Adsorption and dehydrogenation of acetylene were performed as an initial step of carbon nanotube synthesis by using Density Functional Theory calculations with utilization of B3LYP formalism. If activities of different clusters are compared, M-(mu-O)-M-ZSM5 clusters show better performance than the M-ZSM5 clusters for acetylene activation. Activation barriers of Ni-(mu-O)-Ni-ZSM5 and Co-(mu-O)-Co-ZSM5 clusters are lower than those of other ZSM-5 clusters. It can be therefore concluded that Ni-(mu-O)-Ni-ZSM5 and Co-(mu-O)-Co-ZSM5 catalysts can be used for H removal from acetylene as an initial step for carbon nanotube production. (C) 2013 Elsevier Inc. All rights reserved.
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    A Density Functional Theory Study of NO Reduction by C3H8 Aided Selective Catalytic Reduction Method
    (Springer, 2015) Tezsevin, Ilker; Onay, Deniz; Fellah, Mehmet Ferdi; Onal, Isik
    In this theoretical work sequential adsorption of H-2 and O-2 on a Ag (7) (+) cluster surface is first studied and Ag (7) (+) H2O2 cluster co-complex thereby obtained is used for the NO reduction process. This cationic charged silver nano cluster simulates small Ag crystals experimentally detected on gamma-Al2O3 support. For NO reduction, three different mechanisms and intermediate steps of these mechanisms reported in experimental literature are examined. Energy profiles, activation barriers and transition states of the reaction steps involved are studied. Some intermediate steps turned out to have high activation barriers. Hence a combined mechanism selected from the favorable steps found in these three mechanisms is proposed. By using this combined mechanism, reduction of NO to N-2 is achieved.
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    DFT Study of Direct Methanol Oxidation to Formaldehyde by N2O on the [Fe](2+)-ZSM-5 Zeolite Cluster
    (Amer Chemical Soc, 2012) Fellah, Mehmet Ferdi; Onal, Isik
    The mechanistic pathways of direct oxidation of methanol to formaldehyde by N2O were theoretically investigated by means of density functional theory (DFT) over an extra framework species in ZSM-5 zeolite represented by a [Si6Al2O9H14](2-)[Fe](2+) cluster model. The catalytic reactivity of these species is compared with that of mononuclear Fe1+ and (FeO)(1+) sites in ZSM-5 investigated in our earlier work at the same level of theory (J. Catal. 2011, 282, 191). The formation of the grafted species including methoxy on the [Fe](2+) site was calculated to be thermodynamically more stable than on the [FeO](1+) site and less stable than on the [Fe](1+) site. The order of activation barrier values of a critical step, proton transfer from grafted methoxy to form formaldehyde and water, on these sites is as follows: [Fe](1+) > [Fe](2+) >> [FeO](1+). The calculated vibrational frequencies for grafted species on the iron site on the surface are in good agreement with the experimental values.
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    A DFT study on the [VO](1+)-ZSM-5 cluster: direct methanol oxidation to formaldehyde by N2O
    (Royal Soc Chemistry, 2013) Fellah, Mehmet Ferdi; Onal, Isik
    The mechanism of direct oxidation of methanol to formaldehyde by N2O has been theoretically investigated by means of density functional theory over an extra framework species in ZSM-5 zeolite represented by a [(SiH3)(4)AlO4](1) [V-O](1+) cluster model. The catalytic reactivity of these species is compared with that of mononuclear (Fe-O)(1+) sites in ZSM-5 investigated in our earlier work at the same level of theory (J. Catal. 2011, 282, 191). The [V-O](1+) site in ZSM-5 zeolite shows an enhanced catalytic activity for the reaction. The calculated vibrational frequencies for grafted species on vanadium sites on the surface are in good agreement with the experimental values. According to the theoretical results obtained in this study the [V-O](1+) site in the ZSM-5 catalyst has an important role in the direct catalytic oxidation of methanol to formaldehyde by N2O.