Nickel-Induced Promotion Over Hydrogenation Catalysts: Insights from Model Porphyrin Deposition in the Absence of Vanadium Effects

The hydrotreating of residual oil is crucial for producing cleaner fuels, as catalyst deactivation due to metal deposits, particularly nickel (Ni) and vanadium (V), remains a significant challenge. Contrary to the conventional view that metal deposits invariably poison catalysts, our recent studies have observed an unexpected enhancement in the activity of commercial NiMo/Al₂O₃ catalysts during industrial operation. This study systematically investigates the mechanism behind this counter-intuitive phenomenon, with a particular focus on the effects induced by nickel. X-ray photoelectron spectroscopy (XPS) analysis revealed that low-concentration of Ni deposits preferentially formed highly active NiMoS phases during the reaction process, thereby minimized the formation of NiS_x, a typical poisoning species. This increases the number of reactive sulfur sites, boosting the hydrodesulfurization (HDS) activity for 4,6-dimethyldibenzothiophene (4,6-DMDBT), with the conversion rate rising from 17.1 to 73.3%. Similar promoting trends were also observed in conventional NiMo/Al₂O₃ catalysts upon Ni deposition, demonstrating the generality of this effect. Our findings not only provide new insights into the dual role of Ni deposits in catalyst performance but also offer a promising strategy designing industrial metal-poisoning-resistant catalysts with significantly enhanced operational lifespan as well as catalytic performance.