The one-step oxidation of benzene to phenol with nitrous oxide has been studied over a variety of Fe/MFI catalysts at 400 and 450 degreesC. The turnover frequency (TOF) is found to strongly increase with decreasing Fe loading in accordance with the model of mononuclear Fe sites. The TOF is highest for steamed H-MFI catalysts with an iron impurity of Fe/Al = 0.014. A large increase in phenol yield upon steaming H-MFI at 650 degreesC indicates that Fe ions are transferred from lattice to extralattice positions. Treating such catalysts with H2S results in a dramatic decrease of the selectivity to phenol, proving the crucial role of Fe ions. A small residual activity for phenol formation after sulfidation could indicate a different reaction path of low rate or regeneration of Fe sites by oxidation of sulfide groups. In general, three types of Fe sites have been identified in Fe/MFI catalysts: (1) mononuclear Fe, catalyzing phenol formation, (2) dinuclear, oxygen-bridged Fe oxo-ions, catalyzing NO, reduction, and (3) Fe oxide nanoparticles, catalyzing deep oxidation. (C) 2003 Elsevier Inc. All rights reserved.