Physical and Chemical Properties of MoP, Ni₂P, and MoNiP Hydrodesulfurization Catalysts:  Time-Resolved X-ray Diffraction, Density Functional, and Hydrodesulfurization Activity Studies

Synchrotron-based time-resolved X-ray diffraction was used to study in situ the crystalline phases present during the preparation of bulk and silica-supported MoP, Ni2P, and MoNiP by reduction of oxidic precursors in hydrogen. Independent of the type of oxidic precursor used or the presence of silica as a support, the formation of the metal phosphides occurs at temperatures between 600 and 800 °C. Since the common species in all the cases are phosphate-type groups (POx), it seems that their reduction by hydrogen is the final and determining step in the formation of MoP, Ni2P, and MoNiP. Silica-stabilized phosphide phases were detected during the synthesis of Ni2P/SiO2 and MoP/SiO2 catalysts. In the case of Ni2P/SiO2, before the appearance of the final phosphide, strong diffraction lines are observed for Ni12P5. First-principles density functional calculations for bulk MoP, Ni2P, and MoNiP indicate that the Ni−P and Mo−P bonds in these compounds have a small degree of ionic character. For MoP, Ni2P, and Mo...