The Mo/MgO catalysts with different MoO3 loadings were prepared by impregnating MgO support with aqueous ammonium heptamolybdate solution. They were characterized by BET surface analysis, X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman spectroscopy. and X-ray photoelectron spectroscopy (XPS). The highest removal capacity of H2S was obtained with a molybdenum content of 6 wt.%, which was almost close to the theoretical monolayer capacity on MgO support. The surface coverage calculation of MoO3 suggested that a molybdenum oxide addition LIP to a monomolecular layer on MgO support increased the H2S removal capacity of Mo/MgO, but that further increase of Mo-O surface coverage rather decreased it. Raman spectroscopy showed that small domains of MgMoO4 could be present on Mo/MgO with molybdena loadings below 6 wt.%. The crystallites of bulk MgMoO4 and Mg2Mo3O11 became evident on Mo/MgO with molybdena loadings above 15 wt.%, which were confirmed by XRD. TPR profiles showed that the reducibility of Mg molybdate phases was strongly related to the loading amounts of MoO3 on MgO support. Results indicated that tetrahedrally coordinated Mo6+ in well-dispersed MgMoO4 domains could be the active species in the H2S wet oxidation. XPS studies indicated that the H2S oxidation with Mo/MgO could proceed from the redox mechanism (Mo6+ <----> M5+) and that Mo4+ formation, deep reduction, was responsible for the deactivation of Mo/MgO. (C) 2004 Elsevier B.V. All rights reserved.