Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110).
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| Title: | Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO |
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| Authors: | Di Valentin, Cristiana1 cristiana.divalentin@mater.unimib.it, Rosa, Massimo1, Pacchioni, Gianfranco1 |
| Source: | Journal of the American Chemical Society. 8/29/2012, Vol. 134 Issue 34, p14086-14098. 13p. |
| Subjects: | Polymerization, Polymers, Formaldehyde, Physical & theoretical chemistry, Chemical reactions, Intermediates (Chemistry) |
| Abstract: | (WO3)3 clusters deposited on the (110) rutile TiO2 surface are excellent catalysts for the formaldehyde (CH2O) polymerization reaction (J. Phys. Chem. C2010, 114, 17017). The present B3LYP study unravels the possible paths of this catalyzed reaction. According to the stoichiometry of the r-TiO2 surface, the (WO3)3 clusters can be neutral, singly charged, or doubly charged. We find that only neutral (WO3)3 and anionic (WO3)3- clusters are reactive toward CH2O molecules. In both cases it is possible to determine more than one mechanism on the basis of a nucleophilic attack of the formaldehyde O atom to the W ions of the cluster. The reaction proceeds through successive attacks of other CH2O molecules and the formation of acetal and polyacetal intermediates, which inhibits the chain propagation. Only in the case of the anionic (WO3)3- catalyst is a totally different reaction path possible at low temperatures. This path involves the formation of radical species where the unpaired electron is localized on the organic moiety bound to the cluster. The polymer chain propagation follows a radical mechanism with low activation barriers. Thus, a cluster's electron charging speeds up the formaldehyde polymerization at low temperatures. On the basis of these unexpected results, we conclude that electron-rich supports and low working temperatures are the keys to kinetic control of the reaction favoring a fast radical chain propagation mechanism. [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
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| Items | – Name: Title Label: Title Group: Ti Data: Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO<subscript>3</subscript>)<subscript>3</subscript> Clusters on Reduced or Stoichiometric TiO<subscript>2</subscript>(110). – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Di+Valentin%2C+Cristiana%22">Di Valentin, Cristiana</searchLink><relatesTo>1</relatesTo><i> cristiana.divalentin@mater.unimib.it</i><br /><searchLink fieldCode="AR" term="%22Rosa%2C+Massimo%22">Rosa, Massimo</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Pacchioni%2C+Gianfranco%22">Pacchioni, Gianfranco</searchLink><relatesTo>1</relatesTo> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+the+American+Chemical+Society%22">Journal of the American Chemical Society</searchLink>. 8/29/2012, Vol. 134 Issue 34, p14086-14098. 13p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Polymerization%22">Polymerization</searchLink><br /><searchLink fieldCode="DE" term="%22Polymers%22">Polymers</searchLink><br /><searchLink fieldCode="DE" term="%22Formaldehyde%22">Formaldehyde</searchLink><br /><searchLink fieldCode="DE" term="%22Physical+%26+theoretical+chemistry%22">Physical & theoretical chemistry</searchLink><br /><searchLink fieldCode="DE" term="%22Chemical+reactions%22">Chemical reactions</searchLink><br /><searchLink fieldCode="DE" term="%22Intermediates+%28Chemistry%29%22">Intermediates (Chemistry)</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: (WO3)3 clusters deposited on the (110) rutile TiO2 surface are excellent catalysts for the formaldehyde (CH2O) polymerization reaction (J. Phys. Chem. C2010, 114, 17017). The present B3LYP study unravels the possible paths of this catalyzed reaction. According to the stoichiometry of the r-TiO2 surface, the (WO3)3 clusters can be neutral, singly charged, or doubly charged. We find that only neutral (WO3)3 and anionic (WO3)3- clusters are reactive toward CH2O molecules. In both cases it is possible to determine more than one mechanism on the basis of a nucleophilic attack of the formaldehyde O atom to the W ions of the cluster. The reaction proceeds through successive attacks of other CH2O molecules and the formation of acetal and polyacetal intermediates, which inhibits the chain propagation. Only in the case of the anionic (WO3)3- catalyst is a totally different reaction path possible at low temperatures. This path involves the formation of radical species where the unpaired electron is localized on the organic moiety bound to the cluster. The polymer chain propagation follows a radical mechanism with low activation barriers. Thus, a cluster's electron charging speeds up the formaldehyde polymerization at low temperatures. On the basis of these unexpected results, we conclude that electron-rich supports and low working temperatures are the keys to kinetic control of the reaction favoring a fast radical chain propagation mechanism. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1021/ja304661g Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 13 StartPage: 14086 Subjects: – SubjectFull: Polymerization Type: general – SubjectFull: Polymers Type: general – SubjectFull: Formaldehyde Type: general – SubjectFull: Physical & theoretical chemistry Type: general – SubjectFull: Chemical reactions Type: general – SubjectFull: Intermediates (Chemistry) Type: general Titles: – TitleFull: Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110). Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Di Valentin, Cristiana – PersonEntity: Name: NameFull: Rosa, Massimo – PersonEntity: Name: NameFull: Pacchioni, Gianfranco IsPartOfRelationships: – BibEntity: Dates: – D: 29 M: 08 Text: 8/29/2012 Type: published Y: 2012 Identifiers: – Type: issn-print Value: 00027863 Numbering: – Type: volume Value: 134 – Type: issue Value: 34 Titles: – TitleFull: Journal of the American Chemical Society Type: main |
| ResultId | 1 |
