We investigated the phenanthrene (PHE) hydrogenation (HYD) reaction over a Ni-Mo/Al2O3 and a Pt-Pd/Al2O3 catalyst. The catalyst deactivation in the presence of dibenzothiophene (DBT) and/or acridine (ACR) was studied. Near 300degreesC, the main product of the PHE HYD reaction was 1,2,3,4,5,6,7,8-octahydrophenanthrene (1,8-OHP) in the case of the NiMo catalyst and perhydrophenanthrene (PHP) in the case of the PtPd catalyst. Further, the PHE conversion over the NiMo catalyst in the presence of DBT slightly increased with decreasing the DBT concentration (from 1 to 0 wt%). However, the reintroduction of DBT in the feed after a temporary cut did not permit recovery of the initial PHE HYD and DBT hydrodesulfurization (HDS) conversions. It was deduced that the mixed NiMoS phase deteriorated when no sulfur was present in the feed. In the case of the PtPd catalyst, the PHE conversion increased when the DBT concentration decreased. Further, the initial conversions (PHE HYD and DBT HDS) observed after a temporary DBT feed cut and a subsequent DBT reintroduction were substantially recovered. Indeed, contrary to the NiMo catalyst, the PtPd catalyst activity was hindered when sulfur was present in the system, while the absence of sulfur permitted regeneration of the active phase by reduction. In a second part, the effect of the ACR introduction was studied. The ACR introduction led to a drastic decrease in the PHE conversion over the Ni-Mo/Al2O3 catalyst while the decrease was less pronounced over the PtPd catalyst. At the same time, unlike the NiMo catalyst, the Pt-Pd/Al2O3 catalyst showed a drastic decrease in CHB yield (poisoning of the HYD active sites) leading to a drastic decrease in DBT conversion. Moreover, on both catalysts the activity was not fully recovered after the ACR feed was cut, indicating that some HYD catalytic sites were permanently poisoned.