Formation mechanism of active sites with enhanced DBT hydrodesulfurization performance in high-loading NiMoW/SiO2 catalysts during secondary sulfidation

The petroleum refining industry faces increasing challenges in processing sulfur-rich crude oils while meeting stringent environmental regulations. Increasing the metal loading is the most straightforward approach to enhancing catalyst activity. However, under high metal loading conditions, the catalyst tends to form a significant amount of isolated low-activity NiS x and NiO x species. This study presents an effective " sulfidation-oxidation-secondary sulfidation" reconstruction process to enhance the hydrogenation performance of high-loading sulfide NiMoW/SiO 2 catalysts. The migration of active species on the metal surface was induced through high-temperature calcination and sulfur-oxygen transformation processes, leading to the conversion of isolated NiS x and NiO x species into a distinctive NiMoWS/NiS x -SiO 2 composite active phase, with NiS x functioning as a secondary support. Extensive characterization using XRD, HRTEM-EDS, XPS, and DFT calculations revealed that this structural modification substantially increased metal dispersion, sulfidation degree, and hydrogen spillover effects. The optimized NiMoW-300(S) catalyst displayed excellent hydrodesulfurization (HDS) activity and hydrogenation selectivity, with a relative volumetric activity (RVA) 2.49 times higher than that of the conventional NiMo/γ-Al 2 O 3 catalyst, while also demonstrating outstanding stability.