The hydrodenitrogenation of o-propylaniline on MoS2/gamma-Al2O3 and NiMoS/gamma-Al2O3 catalysts proceeds via two parallel routes, i.e., direct denitrogenation (DDN) by C(sp(2))-N bond cleavage to form propylbenzene and hydrogenation (HYD) of the phenyl ring to form propylcyclohexylamine, followed by C(sp(3))-N bond cleavage. Coordinatively unsaturated sites (CUS) at the edges of the sulfide slabs are catalytically active for the DDN. Dibenzothiophene (DBT) decreases the DDN rate, while it is mainly converted via direct desulfurization. Adding Ni to MoS2 increases the CUS concentration and promotes the HYD but inhibits the DDN, suggesting that Ni cations are not involved in the active sites for DDN route. Catalytically active sites for the HYD route are the sites at the basal plane near the edges of the sulfide slabs (brim sites). The presence of DBT strongly increases the HYD rate on NiMoS/gamma-Al2O3, increasing the electron density at the brim sites due the electron pair donor properties of DBT and biphenyl. (C) 2011 Published by Elsevier Inc.