Ethene Epoxidation Selectivity Inhibited by Twisted Oxametallacycle: A DFT Study on Ag Surface-Oxide.
Competitive ethene oxidation pathways are presented for a p(4 x 4) surface-oxide phase on Ag(111) obtained from density functional theory (DFT) calculations. Both parallel routes are found to proceed from a common oxametallacycle intermediate (OMME) in agreement with previous mechanistic studies on...
| Publicado en: | Journal of the American Chemical Society Vol. 127; no. 49; pp. 17207 - 17216 |
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| Autores principales: | , |
| Formato: | Artículo |
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American Chemical Society
12/14/2005
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| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=19332500&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 19332500 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 12/14/2005 vid: 127 iid: 49 pid: 997 pub: American Chemical Society artinfo: ui: 19332500 10.1021/ja051397f ppf: 17207 ppct: 9 formats: tig: atl: Ethene Epoxidation Selectivity Inhibited by Twisted Oxametallacycle: A DFT Study on Ag Surface-Oxide. aug: au: Bocquet, Marie-Laure Loffreda, David affil: Laboratoire de chimie, UMR CNRS 5182, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, F-69364 Lyon, Cedex 07, France. su: Alkenes Oxidation Density functionals Intermediates (Chemistry) Acetaldehyde Epoxy compounds sug: subj: Alkenes Oxidation Density functionals Intermediates (Chemistry) Acetaldehyde Epoxy compounds ab: Competitive ethene oxidation pathways are presented for a p(4 x 4) surface-oxide phase on Ag(111) obtained from density functional theory (DFT) calculations. Both parallel routes are found to proceed from a common oxametallacycle intermediate (OMME) in agreement with previous mechanistic studies on low coverage O adatom phase, although acetaldehyde (AcH) is favored by almost 2 kcal/mol. An even more striking difference with pure metal surface appears with the oxide regeneration pathways, which are found non-rate controlling. Furthermore, a kinetic model is developed on the basis of these DFT calculations and yields 96% selectivity in favor of AcH for a simulation in realistic catalytic conditions (600 K and respective partial pressures of 1 atm for ethene and oxygen reactants). As a key finding, this low ethene epoxide selectivity is proposed to be directly linked to the conformational barrier of the pivotal intermediate. In fact, the elasticity of the ultrathin oxide adlayer enables a twisted OMME structure as a true minimum, which agrees well with orbital prerequisite of the concerted H migration toward AcH. On the contrary, the desired selective ring closure forming ethene epoxide (EO) requires conformational inversion although the eclipsed form lies 2 kcal/mol above. pubtype: Academic Journal doctype: Article src: R language: Slovak refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2005 holdings: @attributes: islocal: N |
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