Investigation of cobalt promotion on TiO2-supported Mo catalysts using a 35S tracer method

A series of CoMo catalysts supported on TiO 2 with various Co/Mo molar ratios were prepared to investigate the relationship between the support and the promoting effect of cobalt. The catalytic activities of these catalysts were measured for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The HDS activity of Mo/TiO 2 catalysts increased remarkably with increased addition of cobalt up to Co/Mo ratio of 0.2 and then increased slightly above this value. The HYD activity of these catalysts remained almost constant with increasing Co/Mo ratio. Sulfur mobility on the sulfided CoMo/TiO 2 catalysts under the reaction conditions was investigated by a 35 S radioisotope tracer method using 35 S-labeled DBT. The rate constants of H 2 S release (k RE ) for Co-promoted catalysts were approximately the same as those for non-promoted Mo catalysts at a given temperature, indicating that the addition of cobalt did not affect the mobility of sulfur over Mo/TiO 2 catalysts. In contrast, the amount of labile sulfur (S 0 ) increased remarkably with the addition of cobalt up to Co/Mo ratio of 0.2 and then increased slightly above this value. The increase in the catalytic activity with the addition of cobalt is probably due to an increase in the number of active sites.