The addition of 4,6-dimethyldibenzothiophene at 10 times the molar ratio to carbazole during carbazole hydrodenitrogenation caused bicyclohexyl, 2-ethylbicyclo[4.4.0]decane and hexylcyclohexane to desorb at the amount of 7.88 µmol g·cat−1 from one site of the sulfided 3.5 wt % phosphorus-doped NiMo/Al2O3 catalyst, while the other site remained unaffected by the addition. The number of special adsorption sites for the 4,6-dimethyldibenzothiophene was estimated.