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The V/MgO catalysts with different V 2 O 5 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 H 2 S 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 m 2 /g and surface coverages of V 2 O 5 of 0:1 $ 2:97. The surface coverage calculation of V 2 O 5 suggested that a vanadia addition up to a monomolecular layer on MgO support increased the H 2 S removal capacity of V/MgO, but the further increase of VO x surface coverage rather decreased that. Raman spectroscopy showed that the small domains of Mg 3 (VO 4 ) 2 could be present on V/MgO with less than 6 wt% vanadia loading. The crystallites of bulk Mg 3 (VO 4 ) 2 and Mg 2 (V 2 O 7 ) 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 2 O 5 were more reducible than those above 15 wt% V 2 O 5 . It indicated that tetrahedrally coordinated V 5þ in well-dispersed Mg 3 (VO 4 ) 2 domains could be the active species in the H 2 S wet oxidation. The XPS studies indicated that the H 2 S oxidation with V/MgO could proceed from the redox mechanism (V 5þ M V 4þ ) and that V 3þ formation, deep reduction, was responsible for the deactivation of V/MgO.

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The effect of CuO loading on CuO/MgO catalysts was investigated for liquidphase oxidation of H 2 S to sulfur. CuO/MgO catalysts were prepared by impregnating MgO with aqueous copper nitrate solution. All of the catalysts were characterized by BET surface analyzer, X-ray diffraction (XRD), and temperature-programmed reduction (TPR). It was observed that the H 2 S removal capacity with respect to CuO loading increased up to 4 wt.%, and then decreased with further increase in CuO loading. CuO addition up to 4 wt.% increased the BET surface areas, but beyond that it was decreased. The XRD showed that well dispersed CuO particles could be present on CuO/MgO at less than 4 wt. % CuO loading. The crystallites of bulk CuO became evident on CuO/MgO with more than 6 wt.% CuO loading, which were confirmed by a XRD. TPR experiments showed that CuO/MgO catalysts with CuO loading above 6 wt.% consisted of two phases of a well-dispersed and crystalline CuO. It was suggested that Cu 2+ in the well-dispersed copper oxide domain could be the active species in the wet oxidation of H 2 S.