Titania-alumina mixed oxides as supports for molybdenum hydrotreating catalysts

Abstract

A series of coprecipitated TiO2-Al2O3 supports containing between 0 and 100% TiO2 were prepared and characterized by various methods. These solids were impregnated with molybdenum and tested in their sulphide form as catalysts in the hydrodesulphurization (HDS) of thiophene. The results showed that in the prepared mixed oxides supports, an interaction between TiO2 and Al2O3 exists and that the coprecipitated solid is different, in its surface properties, from a mechanical mixture of the two oxides. Acidity measurements show that Lewis and not Brønsted sites exist in the mixed oxides. The number of acid sites increases sharply at high TiO2 content. High-resolution electron microscopy shows that a better dispersion of MoS2 on the supports is obtained when the TiO2 content is increased. Activity measurements in the thiophene hydrodesulphurization reaction show that the intrinsic activity, expressed on a molybdenum atom basis, increases sharply at high TiO2 loadings in the mixed oxides supports. Comparison of the activity and acidity measurements point to a correlation between HDS activity and the number of acid sites on the support that affects the dispersion during the impregnation step and the reactivity of the MoS2 sites.