A series of Fe/activated carbon catalysts were prepared by impregnation of activated carbon with aqueous solution of ferric nitrate and employed in phenol hydroxylation to dihydroxybenzenes using hydrogen peroxide as oxidant. The samples were characterized by thermal analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), N-2-adsorption, temperature-programmed oxidation mass spectrometry (TPO-MS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Part of the ferric (Fe(III)) species was reduced to ferrous (Fe(II)) species forming Fe3O4 when the Fe/activated carbon catalyst was heated at 400 degrees C for 3 h in air. Fe3O4 highly dispersed on activated carbon was found to be the active phase for the target reaction. The appearance of ferrous (Fe(II)) species greatly improved the catalytic activity. A phenol conversion of 41.3% and a yield of 36.0% to dihydroxybenzenes were obtained under the following optimal reaction conditions: catalyst amount, 0.1 g; reaction temperature, 30 degrees C; molar ratio of phenol/H2O2, 10.6/9.8; reaction time, 1 h.