Effects of Saccharose Passivation on Oxidation Resistance and Hydrodesulfurization Activity of Sulfurized NiMo/Al₂O₃...

Saccharose (SA) was used as a passivation agent to post-treat an oxidic NiMo/Al₂O₃ hydrotreating catalyst to inhibit the ambient oxidation of the sulfurized catalyst. The effect of SA usage and passivation temperature on oxidation resistance and dibenzothiophene (DBT) hydrodesulfurization (HDS) activity was investigated. Porous carbonaceous deposits with pore sizes of 3-4 nm formed after passivation could effectively prevent ambient air from entering but allow sulfurizing agents and reactants to access metals under high pressure and temperature. SA passivation significantly improved the oxidation resistance of the sulfurized catalyst. Higher SA usage reduced the oxidation resistance, but higher passivation temperatures enhanced it. For the catalyst passivated at 450 °C with a SA/Ni molar ratio of 1.5 (LHT-1.5-450), the oxidation degrees of Mo and Ni sulfides determined by TG were decreased by 50.3% and 53.6%, respectively, after air exposure for 7 days. Additionally, carbonaceous deposits could act as support-like carbon to prevent metals from aggregation and weaken the metal-alumina interaction, resulting in similar activity between the sulfurized catalysts with and without passivation. The passivated catalysts show a considerable reduction in activity loss after exposure to air. LHT-1.5-450 exhibits the lowest activity loss with a 2.7% reduction in DBT removal over each Mo atom, much less than that of the unpassivated catalyst (12.9%). By combining the oxidation resistance of carbonaceous deposits with their promotional effects on activity, the sulfurized catalyst can preserve its activity after exposure to air.