Abstract

SOLIS, D. et al. Synthesis and Characterization of CoMo/Al₂O₃-MgO-(X) catalysts doped with alkaline oxides (K, Li). Superf. vacío [online]. 2007, vol.20, n.4, pp.19-26. ISSN 1665-3521.

CoMo catalysts were prepared using Al₂O₃-MgO-(X) hybrid supports, where X = K₂O or Li₂O. The textural, structural and acid-base properties of these materials were characterized by several techniques. The catalysts were preliminarily evaluated in the hydrodesulfurization (HDS), hydrogenation (HYD) and hydrocracking (HCK) model reactions. The aims of this work are to identify the effect of the addition of an alkaline oxide (either K₂O or Li₂O) to the Lewis acid sites in the CoMo/Al₂O₃-MgO formulation; and on the other hand, to establish a relationship between the acidity and the catalytic performance (hydrogenation function). The results obtained from the pyridine thermodesorption analysis and the n-butyl amine titration techniques show that the incorporation of an alkaline oxide to the CoMo/Al₂O₃-MgO formulation causes a slight decrease in the total number of acid sites (TNAS) with respect to Al₂O₃ and the Al₂O₃-MgO hybrid supports. Both the enhanced textural and structural stability of the CoMo/Al₂O₃-MgO-(X) catalytic formulations, which could be probably attributed to the incorporation of Li or K cations to the MgO framework, stabilizing it, can also be observed. As for the catalytic performance, the CoMo/Al₂O₃-MgO-(X) catalysts containing either Li₂O or K₂O, show a decrease in both the HYD and HYC conversions; however, the formulation containing Li₂O shows the best catalytic behavior due to both the low n-octane yield and the low hydrocracking activity.

Keywords : Lithium; Potassium; Magnesia; Acid sites; Hydrodesulfurization; Hydrogenation.