Influence of aromatics on the hydrodesulfurization reaction pathway of the NiMo/Al₂O₃ catalyst using quasi-in situ characterization techniques

Direct desulfurization (DDS) offers a promising route to reduce hydrogen consumption in diesel desulfurization. Herein, the impact of 1-methylnaphthalene (1-MN) on the conversion of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the selectivity between the hydrogenation desulfurization (HYD) and DDS pathways were systematically investigated. Multiple quasi-in situ characterizations were performed to monitor catalyst structural changes before and after reaction. The introduction of 1-MN exhibited remarkable suppression effects with the rate constants of HYD and DDS pathways being completely inhibited (100%) and diminished (86%), respectively. This pronounced deactivation was mechanistically associated with coke deposition-induced site blocking and 1-MN adsorption, which preferentially compromised the accessibility of catalytically active edge and corner sites. Notably, DDS pathway is less affected by the decrease in active phase concentration compared to the HYD pathway. This behavior is attributed to an increase in sulfur vacancies, enhanced electron deficiency of Ni, and the preferential adsorption of 4,6-DMDBT at corner sites, which collectively favor the DDS route. These results highlight the catalyst design strategy, specifically the increase in sulfur vacancies and tuning the electronic properties of Ni, which can effectively enhance DDS selectivity. This study contributes to the development of hydrotreating catalysts with enhanced DDS pathway selectivity from the perspective of active phase design, which facilitates a reduction in hydrogen consumption.