ABSTRACT: (WO3)3 clusters deposited on the (110) rutile TiO2 surface are excellent catalysts for the formaldehyde (CH2O) polymerization reaction (J. Phys. Chem. C 2010, 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.

DI VALENTIN, C., Rosa, M., Pacchioni, G. (2012). Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110). JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134, 14086-14098 [10.1021/ja304661g].

Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110)

DI VALENTIN, CRISTIANA;PACCHIONI, GIANFRANCO
2012

Abstract

ABSTRACT: (WO3)3 clusters deposited on the (110) rutile TiO2 surface are excellent catalysts for the formaldehyde (CH2O) polymerization reaction (J. Phys. Chem. C 2010, 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.
Articolo in rivista - Articolo scientifico
polimerization, heterogeneous catalysis, WO3, TiO2, radical
English
2012
134
14086
14098
reserved
DI VALENTIN, C., Rosa, M., Pacchioni, G. (2012). Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110). JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134, 14086-14098 [10.1021/ja304661g].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/37361
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