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Free‐Radical Pathways in the Decomposition of Ketones over Polycrystalline TiO 2 : The Role of Organoperoxy Radicals
Author(s) -
Carter Emma,
Carley Albert F.,
Murphy Damien M.
Publication year - 2007
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600484
Subject(s) - radical , cyclopentanone , electron paramagnetic resonance , chemistry , photochemistry , cyclohexanone , crystallite , decomposition , reaction intermediate , acetone , thermal decomposition , organic chemistry , catalysis , crystallography , nuclear magnetic resonance , physics
The oxidative decomposition of various ketones (including acetone, 2‐butanone, 4‐heptanone, cyclopentanone and cyclohexanone) over dehydrated TiO 2 (P25) powder is investigated by electron paramagnetic resonance (EPR) spectroscopy. For the first time, a series of thermally unstable radical intermediates are observed both on the activated and reduced TiO 2 surface, depending on the adopted experimental conditions. These radical intermediates are identified as organoperoxy‐based species of general formula ROO . and RCO 3 . . They are formed by reaction of photogenerated charge carriers (either trapped electrons or trapped holes) with the adsorbed ketones in the presence of molecular oxygen. The organoperoxy intermediates are thermally unstable and decompose at temperatures in the region of 180–250 K. This work demonstrates that free‐radical pathways involving both organoperoxy and superoxide radicals can be responsible for the thermal‐ and photodecomposition of ketones over polycrystalline TiO 2 (P25).