The peculiar electrophilic behaviour of active oxygen formed over Fe-ZSM-5 zeolites upon nitrous oxide decomposition has been investigated in toluene oxidation. Fe-ZSM-5 catalysts have been produced by hydrothermal and post-synthetic techniques, with particular attention given to preparation by chemical vapour deposition of anhydrous FeCl3 into H-ZSM-5. Higher yields of hydroxylated product are possible over Fe-zeolites prepared by hydrothermal synthesis, with para-cresol being the predominant oxygenate formed, though the formation of tars and polycondensed aromatic hydrocarbons retards catalytic activity over time. Oxidation of para-xylene, isopropylbenzene, benzaldehyde, chlorobenzene and phenol demonstrate that the oxidative competition between aliphatic and aromatic C-H bonds is influenced considerably by the steric and electronic nature of the substituent groups. (c) 2004 Elsevier B.V. All rights reserved.