DFT Insights into Mg-Modified Support Effects in Hydrodesulfurization: Mo─O Bond Weakening and Sulfur Vacancy Formation

In this research, the theoretical investigations were conducted to discuss the impact of Mg-modification on the TiO₂/Al₂O₃ supported catalysts for regulating the MoO₃ precursor and the MoS₂ active phase in hydrodesulfurization (HDS). First, the DFT results verified that the Mg-modification could effectively modulate the d-band center of Mo in the MoO₃ precursor. Specifically, on Al₂O₃ (100) and Mg-Al₂O₃ (100) surfaces, the d-band centers of Mo atoms were calculated to be −1.25 eV and −0.04 eV, respectively. This significant shift in d-band center directly affected the adsorption of pre-sulfiding agents, thereby improving the sulfidation process. The COHP results also indicated that the Mo─O bond strength could be weakened after the addition of magnesium, clarifying that the incorporation of magnesium was favorable for the transformation process to the MoS₂ nanoclusters from MoO₃. Additionally, the phase diagrams of sulfur vacancy formation revealed that Mg-modification indeed had a significant impact on the sulfur vacancy formation processes, particularly on the Al₂O₃ (100) surface where the effect was most pronounced. This study presented a synthesized strategy for MoS₂-based catalysts with controllable sulfur vacancy concentration and helped establish rational design principles for future HDS catalysts.