The functionalities of Pt-Mo catalysts in hydrotreatment reactions

The catalytic functionalities of bimetallic Pt-Mo/γ-Al₂O₃ catalysts in hydrotreatment were studied by performing simultaneous and independent dibenzothiophene (DBT) hydrodesulfurization (HDS) and naphthalene hydrodearomatization (HDA) reactions as a function of the activating agent and the MoO₃ content. Pt-Mo/γ-Al₂O₃ catalysts always displayed a higher selectivity to both the direct route of desulfurization (DDS) of DBT and to HDS over HDA than the one exhibited by conventional CoMo and NiMo/γ-Al₂O₃. It was established that for the Pt-Mo catalytic system, the selectivity DDS to the hydrogenation route of desulfurization of DBT can be indirectly described by the selectivity HDS/HDA in simultaneous HDS-HDA catalytic tests. The model of an active phase composed of separated metallic Pt particles, PtS_x species, and sulfided Mo which can either act as independent or cooperative active centers seems to be suitable to explain both the observed kinetic trends and the synergy effect between Pt and Mo.