Cis- and trans-propylcyclohexylamine were identified as primary reaction intermediates of the aliphatic C-N bond cleavage in the hydrodenitrogenation (HDN) network of decahydroquinoline (DHQ). The kinetic parameters of the HDN network were calculated assuming a Langmuir-Hinshelwood mechanism. Three kinds of catalytic sites could be distinguished : aliphatic C(sp(3))-N bond cleavage, (de)hydrogenation of a (aromatic) heterocyclic ring, and alkene hydrogenation. The adsorption constants over NiMo/Al2O3 and NiMoP/Al2O3 catalysts were the same for the C(sp(3))-N bond cleavage site, while different for the hydrogenation sites. The decreased rate constant of the first C(sp(3))-N bond cleavage accounts for the negative effect of phosphorus in the HDN of DHQ. Introduction of Ni to a Mo(P)/Al2O3 catalyst increased the rate constant of the C(sp(3))-N bond cleavage by a factor of 2, and that of alkene hydrogenation by a factor of 6.