Sulfidability and HDS activity of Co-Mo/Al 2O 3 catalysts

Abstract

A series of Co-Mo/Al 2O 3 catalysts were investigated using Temperature-Programmed Sulfiding and HDS activity measurements. The effect of changing the cobalt content and the temperature of calcination on sulfidability, catalyst structure and thiophene HDS activity was studied in detail. It is found that the effect on the HDS activity of higher temperatures of calcination depends on the Co content: at low Co content the activity drops sharply, for intermediate Co loadings the decline is not as pronounced, while at high Co contents an increase in HDS activity is found when the temperature of calcination is raised above 785 K. The typical “synergistic” maximum observed when HDS activity is plotted versus Co content (or Co/Mo ratio) does not occur when catalysts are calcined above 785 K. Instead HDS activity rises monotonously with an increase in Co content. At least five Co species can be present in sulfided Co-Mo/Al 2O 3 catalysts but HDS activity can mainly be attributed in all catalysts to one particular phase which contains sulfided Mo and Co. After calcination at 1125 K the activity is increased because the interaction between the active phase and the support has weakened.