Abstract

High surface area MoO₃/MgO catalysts (200–270 m² g⁻¹) have been prepared by the reaction of MgO with the impregnation slurry (NH₄)₆Mo₇O₂₄/methanol. Molybdena was deposited and NH₃ was evolved. The texture of water sensitive MgO was stable in the slurry. The impregnation reaction was limited to the MgO surface at 25 °C where each Mo atom occupied about 0.24–0.28 nm² at saturation. However, impregnation probably continued into subsurface layers of MgO at 65 °C where the saturation loading corresponded to 0.13–0.16 nm² per Mo atom. Gradual penetration of molybdena into MgO extrudates indicated that the surface reaction between dissolved (NH₄)₆Mo₇O₂₄ and MgO was fast and the rate determining step of impregnation was dissolution or diffusion of (NH₄)₆Mo₇O₂₄. The MoO₃/MgO catalysts were prepared using various particle sizes of MgO, various loadings of MoO₃, different temperatures and impregnation times. The activity of the best MoO₃/MgO catalysts in the hydrodesulfurization of benzothiophene was similar to the activity of the commercial conventional hydrodesulfurization catalyst MoO₃/Al₂O₃.