The dual role of Ni: From promotion to suppression of hydrodesulfurization in NiMoW catalysts

Ni loading governs the structure and electronic properties of NiMoWS phases. • Moderate Ni promotes an optimal -SH/CUS balance at Mo(W) edges. • Excess Ni disrupts -SH/CUS matching, suppressing hydrodesulfurization activity. Stringent environmental regulations and the need to process heavy, sour crudes are driving the development of advanced hydrodesulfurization (HDS) catalysts, particularly Ni-promoted Mo/W sulfide catalysts. Although the promotional role of Ni in sulfide HDS catalysts is well recognized, the origin of activity suppression under Ni-rich conditions remains unclear. In this work, a series of high-loading NiMoW/SiO 2 catalysts with varying Ni contents were investigated to clarify why further Ni addition leads to activity suppression in the HDS reaction under Ni-rich conditions. Combined Py-IR, EPR, Raman, XPS, and DFT analysis reveal that the key factor is the balance between -SH and coordinatively unsaturated sites (CUS) on the sulfide surface. An appropriate Ni content increases the abundance of catalytically effective sites while maintaining favorable -SH/CUS matching, leading to the highest HDS activity for Ni 1 Mo 1 W 1 . In contrast, excess Ni causes a continuous increase in the relative abundance of -SH species without a corresponding effective generation of additional CUS sites, thereby disrupting the -SH/CUS balance and suppressing DBT conversion. The optimized Ni 1 Mo 1 W 1 catalyst also exhibited stable performance over five cycles and a 1.47-fold higher relative volume activity than the industrial NiMo/γ-Al 2 O 3 reference catalyst (8 MPa, 300 °C), and good stability during a 360 h real-oil hydrotreating test. This work identifies -SH/CUS imbalance as a major origin of activity suppression under Ni-rich conditions in NiMoW catalysts. Download: Download high-res image (170KB) Download: Download full-size image