Browsing by Author "van Santen, Rutger A."

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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 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.
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.
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.