Dibenzothiophene hydrodesulfurization activity and surface sites of silica-supported MoP, Ni₂P, and Ni-Mo-P catalysts

Silica-supported binary and ternary phosphides, MoP/SiO₂, Ni₂P/SiO₂, and Ni-Mo-P/SiO₂ have been prepared and characterized by X-ray diffraction (XRD), BET surface area, CO chemisorption, transmission electron microscopy (TEM), and infrared spectroscopy (IR). The hydrodesulfurization (HDS) activities of dibenzothiophene (DBT) were measured and compared at 593 K and 3.0 MPa for MoP/SiO₂, Ni ₂P/SiO₂, and Ni-Mo-P/SiO₂ catalysts with different Mo and Ni loadings. The activities of the phosphides follow the order Ni₂P/SiO₂ > Ni-Mo-P/SiO₂ > MoP/SiO ₂. The Ni sites in the Ni-Mo-P/SiO₂ catalysts play a major role in the conversion of DBT, and the activity of the catalysts increases with increasing Ni content. This is different from sulfides, nitrides, and carbides, as no synergetic effect is observed between the phosphided Ni and the Mo atoms. The surface of these phosphide catalysts is partially sulfided forming a surface phosphosulfide phase, while the bulk structure of the phosphides is maintained in the HDS reactions.