Inhibition effect of nitrogen compounds on CoMoP/Al2O3 catalysts with alkali or zeolite added in hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

The HDS of DBT as a reference probe molecule is thought to proceed first through direct desulfurization pathways, then to hydrogenolysis. A significant amount of benzene was detected in the case of CoMoP/zeolite-Al2O3. The HDS of 4,6-DMDBT over CoMoP/zeolite-Al2O3 in the absence of quinoline proceeds through a very complex mechanism that involves several other reactions, such as isomerization, alkylation, and hydrocracking. This can probably be attributed to the acidic properties of zeolite. In the presence of quinoline, a strong inhibition effect was observed for all the catalysts. The inhibition effects of quinoline on CoMoP/Al2O3-Li were smaller than its effects on the other catalysts; this fact resulted in the enhancement of HDS activity. Moreover, from the XPS investigations we can conclude that CoMoP/Al2O3-Li showed a relatively higher sulfidation degree for both Mo and Co. Thus, it seems to have a relatively higher catalytic activity.