The interaction of a coadsorbed mixture of acetone and oxygen with a clean oxidized polycrystalline sample
of TiO2 (P25) was investigated using electron paramagnetic resonance (EPR) spectroscopy. UV illumination
of the sample at low temperature (100 K) generated an unstable radical intermediate at the dehydrated (and
hydrated) TiO2 surface. The radical decayed irreversibly at temperatures greater than 150 K but was regenerated
by subsequent irradiation at low temperatures. Using a series of isotopically labeled gases (CH3COCH3, CD3COCD3, 16O2, and 17O2) to aid in the interpretation of the EPR spectrum, the radical was identified as an
alkylperoxy species RCH2OO• with the spin Hamiltonian parameters of g
1 = 2.0345, g
2 = 2.0070, g
3 =
2.0010, H
A
1 = 0.34 mT, H
A
2 = 0.10 mT, H
A
3 = 0.29 mT, 17Ο
A
||(i) = 9.45 mT (for RO17O•), and 17O
A
||(ii) =
5.52 mT (for R17OO•). By consideration of the different mechanistic pathways involved in the oxidation of
acetone, it was concluded that the observed radical is generated initially by hole transfer to the adsorbed
acetone and the identity of the unstable peroxy intermediate must be CH3COCH2OO•.
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