Catalytic oxidation of benzene to phenol by nitrous oxide over Fe-MFI zeolites was studied in relation to the active oxygen species taking part in the oxidation. A linear dependence of the reaction rate on the concentration of independently identified active sites generating O-radicals (a sites) was obtained within a broad range of values. The dependence is interpreted as convincing evidence of the O- involvement in the catalytic (not only stoichiometric) oxidation of benzene to phenol. This conclusion is of particular importance in connection with a long discussion in the literature on a possible role of O- radicals in selective oxidation catalysis over V and Mo oxides. Reliable evidence of the catalytic role of O- obtained with zeolites may renew general interest in the once-suggested but not recognized role of radical oxygen in oxidation over widely used metal oxide catalysts. (c) 2006 Elsevier Inc. All rights reserved.