The V/MgO catalysts with different V2O5 loadings were prepared by impregnating MgO with aqueous vanadyl sulfate solution. All of the catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). It was observed that the 2S removal capacity with respect to vanadia content increased up to 6 wt%, and then decreased with further increase in vanadia loading. The prepared catalysts had BET surface areas of 11.3-95.9 m2/g and surface coverages of V2O5 of 0.1-2.97. The surface coverage calculation of V2O5 suggested that a vanadia addition up to a monomolecular layer on MgO support increased the H2S removal capacity of V/MgO, but the further increase of VOx surface coverage rather decreased that. Raman spectroscopy showed that the small domains of Mg3(VO4)2 could be present on V/MgO with less than 6 wt% vanadia loading. The crystallites of bulk Mg3(VO4)2 and Mg2(V2O7) became evident on V/MgO catalysts with vanadia loading above 15 wt%, which were confirmed by a XRD. The TPR experiments showed that V/MgO catalysts with the loading below 6 wt% V 2O5 were more reducible than those above 15 wt% V 2O5. It indicated that tetrahedrally coordinated V 5+ in well-dispersed Mg3(VO4)2 domains could be the active species in the H2S wet oxidation. The XPS studies indicated that the H2S oxidation with V/MgO could proceed from the redox mechanism (V5+ ↔ V4+) and that V3+ formation, deep reduction, was responsible for the deactivation of V/MgO.
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