Abstract: Effect of basic nitrogen compound (quinoline) and non-basic nitrogen compound (indole) on the catalytic activity and product selectivity of the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were investigated over sulfided NiW/Al2O3 catalyst. The results for DBT and 4,6-DMDBT were varied. With the existence of nitrogen compounds, the HDS reactions of DBT enhanced due to the improved DDS reaction activity, yet for 4,6-DMDBT, its HDS reaction activity decreased significantly. The adsorption of nitrogen compounds on the hydrogenation active sites of catalyst could inhibit the adsorption of sulfur compounds, resulting in the suppression of HYD reactions, and simultaneously, the accessible active sites on the catalyst surface seemed to be redistributed. In this case, the molecule size and stereo structure of the sulfur compounds become essential. Smaller size DBT molecules could access hydrogenolysis active sites via sulfur atom easily and its hydrogenolysis activity improved; large 4,6-DMDBT molecules were suffocated by overcrowding nitrogen compounds to access active sites, thus the hydrogenolysis activity of 4,6-DMDBT decreased with the increase of nitrogen content.

Key words: nitrogen compound, dibenzothiophene, 4,6-dimethyldibenzothiophene, hydrodesulfurization