Investigation of Cobalt Promotion on TiO2-supported Mo Catalysts Using a 35S Tracer Method.

Abstract

A series of CoMo catalysts supported on TiO2 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/TiO2 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/TiO2 catalysts under the reaction conditions was investigated by a 35S radioisotope tracer method using 35S-labeled DBT. The rate constants of H2S release (kRE) 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/TiO2 catalysts. In contrast, the amount of labile sulfur (S0) 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.