Ultra-deep hydrodesulfurization on MoS₂ and Co₀.₁MoS₂: Intrinsic vs. environmental factors

A hydrogenation index (HI), measured in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), is used to estimate the intrinsic hydrogenation selectivities of MoS₂, Co₀.₁MoS₂, and two supported HDS catalysts. The HI and catalyst activity for desulfurizing 4,6-diethyl-DBT follow the same trend: MoS₂≫Co₀.₁MoS₂≫supported catalysts. For desulfurizing a petroleum fraction rich in 4,6-alkyl-DBTs and 4-alkyl-DBTs, the activity decreases as follows: Co₀.₁MoS₂>supported catalysts≫MoS₂. These results introduce an apparent conundrum: MoS₂ has such a high hydrogenation power and activity for desulfurizing 4,6-diethyl-DBT, why does it perform poorly in real-feed tests? This conundrum is resolved by showing that an ultra-deep HDS catalyst requires an optimum balance between an intrinsic factor (hydrogenation function) and an environmental factor (tolerance of organonitrogen). Incorporating Co into MoS₂ lowers the hydrogenation function of MoS₂ and hence improves tolerance of organonitrogen. This conclusion corroborates the prediction of an early modeling study.