Browsing by Author "Onal, Isik"

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C-H Bond Activation of Methane on M- and Mo-Zsm (M = Ag, Au, Cu, Rh and Ru) Clusters: a Density Functional Theory Study
(Elsevier, 2011) Fellah, Mehmet Ferdi; Onal, Isik
Density functional theory (DFT) calculations were carried out in a study of C-H bond activation of methane on [(SiH3)(4)AlO4(M, MO)] (where M = Ag, Au, Cu, Rh and Ru) cluster models representing ZSM-5 surfaces. The following activity order of clusters with respect to their activation barriers could be qualitatively classified: Au >> Rh > Cu = Ru > Ag for metal-ZSM-5 clusters and Ag > Cu > Au >> Rh > Ru for Metal-O-ZSM-5 clusters. Therefore, activation barriers based on transition state calculations showed that Ag-O-, Cu-O- and Au-O-ZSM-5 clusters (4, 5, and 9 kcal/mol, respectively) are more active than all the other clusters for C-H bond activation of methane. (C) 2011 Elsevier B. V. All rights reserved.
A Comparative Experimental and Density Functional Study of Glucose Adsorption and Electrooxidation on the Au-Graphene and Pt-Graphene Electrodes
(Pergamon-elsevier Science Ltd, 2020) Caglar, Aykut; Duzenli, Derya; Onal, Isik; Tersevin, Ilker; Sahin, Ozlem; Kivrak, Hilal
At present, the graphene is covered on Cu foil with the 5 sccm hexane (C6H14) flow rate, 50 sccm hydrogen (H-2) flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil is then covered onto few-layer ITO electrode. Furthermore, the Pt and Au metals are electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes are characterized by Raman spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-Ray analysis (SEM-EDX). The graphene structure is approved via Raman analysis. Au, Pt, and graphene network are openly visible from SEM results. In addition, glucose (C6H12O6) electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. As a result, Pt-graphene/ITO indicates the best C6H12O6 electrooxidation activity with 9.21 mA cm(-2) specific activity (highly above the values reported in the literature). In all electrochemical measurements, Pt-graphene/ITO exhibits best electrocatalytic activity, stability, and resistance compared to the other electrodes. The adsorption of the C6H12O6 molecule is examined theoretically over metal atom (gold and platinum)-doped graphene surfaces using the density functional theory (DFT) method. The interaction between C6H12O6 molecule and OH adsorbed Pt-doped surface is stronger than that of OH adsorbed Au-doped graphene surface thermodynamically according to the reaction energy values. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
A Density Functional Study of 1, 1, 5-Tris(4
(Wiley, 2010) Fellah, Mehmet Ferdi; Onal, Isik
The optimized molecular structural parameters and UV-vis, IR and Raman spectra of a dye molecule with an open formula of 1,1,5-Tris(4-dimethylaminophenyl)-3-methyl-divinylene are determined by means of density functional theory (DFT) calculations using B3LYP/6-31G** formalism. Neutral and cationically charged molecules are used for DFT computations. C-C, C-C, and N-C bond distances of dimethylaminophenyl groups of the dye molecule are in reasonable agreement with the experimental and theoretical C-C, C=C, and N-C bond lengths of the group reported in the literature. Because Vis-NIR region is near UV-Vis region in the electromagnetic spectra, calculated maximum wavelengths of UV-vis spectra are close to those of the experimental VIS-NIR spectra reported. C-C stretching frequencies calculated for dimethylaminophenyl, alkene, and benzene ring groups are also in good agreement with experimentally reported values. All calculated frequencies fall within 2.2% of the experimental frequency region. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 1047-1047, 2010.
A Density Functional Theory Study of C-H Bond Activation of Methane on a Bridge Site of M-O Clusters (M = Au, Ag, Fe and Cu)
(Elsevier, 2011) Kurnaz, Emine; Fellah, Mehmet Ferdi; Onal, Isik
C-H bond activation of methane on a bridge site M-O-M- of ZSM-5 (M = Au, Ag, Fe and Cu) clusters has been performed by means of Density Functional Theory (DFT) calculations with the utilization of [Si6Al2O9H14(M-O-M](2+) (where M = Au, Ag, Fe and Cu) cluster models representing ZSM-5 surfaces. According to the activation barrier data based on TS calculations. The following activity order of clusters with respect to their activation barriers could be classified: Ag approximate to Au > Cu Fe for Metal-O-Metal-ZSM-5 clusters. Activation barriers for C-H bond activation of methane on Au-O-Au- and Ag-O-Ag-ZSM-5 clusters are calculated as 4.83 and 4.79 kcal/mol, respectively. These values are lower than the activation barrier values for C-H bond activation on Cu-O-Cu-ZSM-5 and Fe-O-Fe-ZSM-5 which are 9.69 and 26.30 kcal/mol, respectively. Activation process is exothermic on Au-O-Au-, Cu-O-Cu-, and Fe-O-Fe-ZSM-5 clusters whereas it is endothermic on Ag-O-Ag-ZSM-5 cluster. (C) 2010 Elsevier Inc. All rights reserved.
A Density Functional Theory Study of Direct Oxidation of Benzene To Phenol by N2o on a [feo]1+-Zsm Cluster
(Amer Chemical Soc, 2010) Fellah, Mehmet Ferdi; Onal, Isik; van Santen, Rutger A.
Density functional theory calculations were carried out in a study of the oxidation of benzene to phenol by N2O on a model (FeO)(1+)-ZSM-5 cluster: the [(SiH3)(4)AlO4(FeO)] cluster. This cluster models the reactivity of Fe3+ oxidic clusters. Results are to be compared with an earlier study (J. Phys. Chem. C 2009, 113, 15307) on a model Fe2+-ZSM-5 cluster. The true activation energies for the elementary reaction step in which phenol is produced appear to be comparable. The major difference between the two systems appears to be the relative stabilities of the intermediate phenolates. On the Fe3+-containing cationic cluster, this appears to be uniquely stable. This result suggests that the experimentally observed preference of Fe2+ sites over (FeO)(1+) on ZSM-5 for benzene oxidation to phenol by N2O is due to the reduced formation of adsorbed phenolate, which is possibly an intermediate for deactivation.
A Density Functional Theory Study of Ethylene Adsorption on Ni10(111), Ni13(100) and Ni10(110) Surface Cluster Models and Ni13 Nanocluster
(Elsevier Science Bv, 2010) Yilmazer, Nusret Duygu; Fellah, Mehmet Ferdi; Onal, Isik
Ethylene adsorption was studied by use of DFT/B3LYP with basis set 6-31G(d, p) in Gaussian' 03 software. It was found that ethylene has adsorbed molecularly on all clusters with pi adsorption mode. Relative energy values were calculated to be -50.86 kcal/mol, -20.48 kcal/mol, -32.44 kcal/mol and -39.27 kcal/mol for Ni-13 nanocluster, Ni-10(1 1 1), Ni-13(1 0 0) and Ni10(1 1 0) surface cluster models, respectively. Ethylene adsorption energy is inversely proportional to Ni coordination number when Ni-10(1 1 1), Ni-13(1 0 0) and Ni-10(1 1 0) cluster models and Ni-13 nanocluster are compared with each other. (C) 2010 Elsevier B.V. All rights reserved.
A Density Functional Theory Study of Oxidation of Benzene To Phenol by N2o on Fe- and Co-Zsm Clusters
(Tubitak Scientific & Technological Research Council Turkey, 2009) Fellah, Mehmet Ferdi; Onal, Isik
Density functional theory (DFT) calculations were carried out in the study of oxidation of benzene to phenol by N2O on relaxed [(SiH3)(4)AlO4M] (where M=Fe, Co) cluster models representing Fe- and Co-ZSM-5 surfaces. The catalytic cycle steps are completed for both Fe-ZSM-5 and Co-ZSM-5 clusters. The general trend of the results that were obtained in terms of activation barriers for the Fe-ZSM-5 cluster is in agreement with the experimental and theoretical literature. It was observed that the phenol formation step is the rate-limiting step for both clusters and Co-ZSM-5 surface has a lower activation barrier than the Fe-ZSM-5 surface (i.e. 35.82 kcal/mol vs. 45.59 kcal/mol, respectively).
A Dft Study of Direct Oxidation of Benzene To Phenol by N2o Over [fe(μ-O)fe]2+ Complexes in Zsm-5 Zeolite
(Amer Chemical Soc, 2011) Fellah, Mehmet Ferdi; Pidko, Evgeny A.; van Santen, Rutger A.; Onal, Isik
Density functional theory (DFT) calculations were carried out in a study of the mechanism of benzene oxidation by N2O to phenol over an extra framework dimeric [FeOFe](2+) species in ZSM-5 zeolite represented by a [Si6Al2O9H14(Fe(mu-O)Fe)] cluster model. The catalytic reactivity of such a binuclear species is compared with that of mononuclear Fe2+ and (FeO)(+) sites in ZSM-5 investigated in our earlier works at the same level of theory (J. Phys. Chem. C 2009, 113, 15307; 2010, 114, 12580). The activation energies for the elementary reaction step involved in the benzene hydroxylation over the binuclear and the mononuclear iron sites are comparable. The major difference in the catalytic behavior of the systems considered is related to the ability of Fe3+-containing sites to promote side reactions leading to the active site deactivation. Regeneration of the active site via the phenol desorption is much less favorable than its dissociation resulting in the formation of very stable grafted phenolate species on both the [Fe(mu-O)Fe](2+) and (FeO)(+) sites. In the case of Fe2+ sites such an alternative reaction path does not exist resulting in their stable catalytic performance. Benzene hydroxylation and phenol formation over the binuclear (Fe(mu-O)Fe)(2+) sites in ZSM-5 are promoted in the presence of water. These computational findings are consistent with the experimental observations and allow their rationalization at the molecular level.
Direct Gas-Phase Epoxidation of Propylene To Propylene Oxide Through Radical Reactions: a Theoretical Study
(Elsevier, 2010) Kizilkaya, Ali Can; Fellah, Mehmet Ferdi; Onal, Isik
The gas-phase radical chain reactions which utilize O-2 as the oxidant to produce propylene oxide (PO) are investigated through theoretical calculations. The transition states and energy profiles were obtained for each path. The rate constants were also calculated. The energetics for the competing pathways indicate that PO can be formed selectively due to its relatively low activation barrier (9.3 kcal/mol) which is in a good agreement with the experimental value (11 kcal/mol) of gas-phase propylene epoxidation. The formation of the acrolein and combustion products have relatively high activation barriers and are not favored. These results also support the recent experimental findings. (C) 2010 Elsevier B.V. All rights reserved.
Direct Methane Oxidation To Methanol by N2o on Fe- and Co-Zsm Clusters With and Without Water: a Density Functional Theory Study
(Amer Chemical Soc, 2010) Fellah, Mehmet Ferdi; Onal, Isik
Density functional theory (DFT) calculations were carried Out ill a Study of oxidation of methane to methanol by N2O on the Fe- and Co-ZSM-5 clusters. The catalytic cycle steps have been Studied oil model Clusters ((SiH3)(4)AlO4M) (where M = Fe, Co). Calculations indicate very low methanol selectivity Without water and increasing rate of methanol formation with water. These results are in qualitative agreement with the experimental literature. The methanol formation step is also found to be the rate-limiting step, and this result is in agreement with other theoretical work. Co-ZSM-5 cluster has a lower activation barrier when compared to that of Fe-ZSM-5 cluster (49 kcal/mol vs 53 kcal/mol). Activation barrier values decrease to 48 and 39 kcal/mol for Fe- and Co-ZSM-5 Clusters, respectively, in the presence of water molecule adsorbed after the formation of I hydroxy group oil the ZSM-5 surface. The methanol formation step is the most difficult reaction for both Clusters with and without water.
Epoxidation of Ethylene by Silver Oxide (Ag2o) Cluster: a Density Functional Theory Study
(Springer, 2011) Fellah, Mehmet Ferdi; van Santen, Rutger A.; Onal, Isik
Density functional theory (DFT) calculations were employed to study epoxidation of ethylene on a [Ag14O9] cluster model representing silver oxide (001) surface. Theoretical results obtained in this study showed that formation paths of acetaldehyde and vinyl alcohol have higher activation barriers than that of ethylene oxide formation path on silver oxide (35 and 35 vs. 20 kcal/mol). Formation of the ethylene oxometallocycle intermediate is found to have a low probability on Ag2O(001) surface. The essential reason for this may be lower basicity of surface oxygen atom on silver oxide surface and the absence of a surface vacancy position to activate ethylene. Adsorbed EO is formed on Ag2O surface cluster without an activation barrier. The activation barriers of the rate-limiting steps for the production of EO mechanisms (via ethyleneoxy and non-activated paths, 20 vs. 14 kcal/mol) are in relatively good agreement with the experimental activation energy values (14, 17 and 22 kcal/mol) reported for EO formation on silver catalyst.
Epoxidation of Propylene on a [Ag14o9] Cluster Representing Ag2o (001) Surface: a Density Functional Theory Study
(Springer, 2012) Fellah, Mehmet Ferdi; Onal, Isik
Density functional theory calculations were employed to study partial oxidation of propylene on a [Ag14O9] cluster representing Ag2O (001) surface for which positive effect for ethylene oxide formation has been reported in our earlier work at the same level of theory (Fellah et al., Catal Lett 141: 762, 2011). Propylene oxide (PO), propanal, acetone and G-allyl radical formation reaction mechanisms were investigated. P-allyl formation path and two propylene adsorption paths resulting in PO formation are competing reactions on silver oxide (001) surface because of their comparable activation barriers (9, 8 and 9 kcal/mol, respectively) while P-allyl formation path is generally a more favorable path on Ag (111) surface as reported in previous theoretical literature. SO2 adsorption calculations indicate that silver oxide has lower Lewis basicity relative to oxygen atom adsorbed on silver. Calculations also showed that surface oxygen atom of Ag2O (001) has a higher spin density compared to that of oxygen atom adsorbed on Ag (111), which indicates that oxygen atom on Ag2O (001) cluster has a more radical character.
Glucose Electrooxidation Modelling Studies on Carbon Nanotube Supported Pd Catalyst With Response Surface Methodology and Density Functional Theory
(Pergamon-elsevier Science Ltd, 2022) Kaya, Sefika; Ulas, Berdan; Duzenli, Derya; Onal, Isik; Er, Omer Faruk; Yilmaz, Yonca; Kivrak, Hilal
In this study, carbon nanotube supported Pd catalysts (Pd/CNT) are synthesized at different weight percentages by the sodium borohydride (NaBH4) reduction method to investigate catalytic performance of glucose electrooxidation reaction. 0.5% Pd/CNT, 3% Pd/CNT, and 7% Pd/CNT catalysts are characterized by using X-ray diffraction (XRD), electron microscopy with energy dispersive X-ray (SEM-EDX), and N2 adsorption-desorption measurements. The average particle size and surface area of 3% Pd/CNT catalyst are determined as 46.33 nm and 129.48 m2/g, respectively. Characterization results indicate that Pd/CNT catalysts are successfully prepared by NaBH4 reduction method. Cyclic voltammetry measurements are performed to investigate the effect of Pd loading for the glucose electrooxidation. CV results reveal that 3% Pd/CNT catalyst exhibits best glucose electrooxidation activity. Following this, experimental optimization is performed to obtain maximum glucose electrooxidation activity via response surface methodology (RSM). Estimated and experimental specific activities at optimum experimental conditions are assigned as 6.186 and 5.832 mA/cm2, respectively. To understand the glucose electrooxidation activity on the surface of Pd/CNT, surface modeling is also performed with density functional theory (DFT) method to investigate adsorption of glucose molecule on CNT supported Pd surface. The DFT results emphasize that the addition of Pd atom to the CNT structure significantly improves the catalytic performance in glucose electrooxidation.
Ni55 Nanocluster: a Density Functional Theory Study of the Binding Energy of Nickel and Ethylene Adsorption
(Tubitak Scientific & Technological Research Council Turkey, 2012) Yilmazer, Nusret Duygu; Fellah, Mehmet Ferdi; Onal, Isik
Ethylene adsorption on a Ni-55 nanocluster was studied by Weal IS of the density functional theory (DFT)/B3LYP using the basis sets of 6-31G(d,p) and 86-411(41d)G in Gaussian 03. The Ni-55 nanocluster was found to have a distorted icosahedral geometry, in accordance with the experimental findings. The binding energy value for the Ni-55 nanocluster was calculated to be 3.51 eV/atom using equilibrium geometry calculations. The estimated bulk nickel binding energy was in reasonable agreement with the experimental value (4.85 versus 4.45 eV/atom). In addition, equilibrium geometry calculations were performed for ethylene adsorption on the Ni-55 nanocluster for 2 different coordination numbers of 6 and 8 with pi-adsorption modes. The related adsorption energies were computed as -0.87 and -0.68 eV, respectively.
A Novel Experimental and Density Functional Theory Study on Palladium and Nitrogen Doped Few Layer Graphene Surface Towards Glucose Adsorption and Electrooxidation
(Pergamon-elsevier Science Ltd, 2021) Caglar, Aykut; Duzenli, Derya; Onal, Isik; Tezsevin, Ilker; Sahin, Ozlem; Kivrak, Hilal
At present, few layer graphene (G) and nitrogen doped few layer graphene (N doped-G) are firstly coated on Cu foil via chemical vapor deposition (CVD) method and G and N doped-G coated Cu foil is transferred to the indium tin oxide (ITO) substrate surface to obtain electrodes. Pd metal is electrodeposited onto the N doped-G/ITO electrode (Pd-N doped-G/ITO). Pd-N doped-G/ITO electrode are characterized with advanced surface characterization methods such as Raman spectroscopy and SEM-EDX. Characterization results reveal that G and N structures are succesfully obtained and the presence of Pd on Pd-N doped-G/ITO is confirmed with SEM-EDX mapping. The cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) are employed to examine glucose electrooxidation of G/ITO, N-doped G/ITO, and Pd-N-doped G/ITO electrodes. P-N-dopedG/ITO electrode exhibits the best glucose electrooxidation activity with 2 mA/cm(2) specific activity. Density functional theory (DFT) calculations are also carried out to better understand the interaction of the molecules on Pd modified G (Pd-G) and Pd modified N-doped G (Pd-3NG) surfaces.
An Oniom and Dft Study of Water Adsorption on Rutile Tio2 (110) Cluster
(Wiley-blackwell, 2011) Erdogan, Rezan; Fellah, Mehmet Ferdi; Onal, Isik
Density functional theory (DFT) calculations performed at ONIOM DFT B3LYP/6-31G**-MD/UFF level are employed to study molecular and dissociative water adsorption on rutile TiO2 (110) surface represented by partially relaxed Ti25O37 ONIOM cluster. DFT calculations indicate that dissociative water adsorption is not favorable because of high activation barrier (23.2 kcal/mol). The adsorption energy and vibration frequency of both molecularly and dissociatively adsorbed water molecule on rutile TiO2 (110) surface compare well with the values reported in the literature. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 174-181, 2011
Oxidation of Benzene To Phenol by N2o on an Fe2+-Zsm Cluster: a Density Functional Theory Study
(Amer Chemical Soc, 2009) Fellah, Mehmet Ferdi; van Santen, Rutger A.; Onal, Isik
Density functional theory (DFT) calculations were carried out in a study of the oxidation of benzene to phenol by N2O on an Fe2+-ZSM-5 cluster. The catalytic cycle has been studied oil a model [Si6Al2O9H14Fe] cluster. It is found that Fe2+ is preferred over Fe1+ as a site for phenol oxidation. A high desorption value of 126.4 kJ/mol suggests that at low temperature phenol desorption is the rate limiting step on the Fe2+-ZSM-5 cluster. It competes with the N2O decomposition step. The computed activation energy for phenol desorption is in good agreement with the experimental activation energy value of 125.94 kJ/mol reported in the literature for benzene oxidation to phenol by N2O on Fe-ZSM-5.