Effect of Sodium on Ni-Promoted MoS2 Catalyst for Hydrodesulfurization Reaction: Combined Experimental and Simulation Study

The presence of Na in Ni-promoted MoS2 provides an interesting case study as Na gets inadvertently incorporated during the reverse micelle synthesis of the nanocatalyst. The effect of Na in Ni-promoted MoS2 during hydrodesulfurization (HDS) of dibenzothiophene (DBT) is investigated here through combined experiment and density functional theory (DFT) studies. Computations suggest that Na replaces otherwise more HDS active Ni sites, which are likely to be present as metal atoms on S edge or on metallic edge sites of MoS2(100). The presence of Na dopant instead of Ni results in the molecular hydrogen dissociation step becoming more endothermic, leading to the lowering of HDS catalytic activity. The HDS of DBT decreases with an increase of Na concentration in Ni-promoted MoS2. However, the concentration of Na has a nonmonotonic effect on the selectivity of different mechanistic pathways of HDS. The selectivity toward a cost-effective direct desulfurization (DDS) pathway increases up to an optimal Na concentration, after which the selectivity decreases as observed from experiments and corroborated by DFT studies. However, DDS selectivity always remains higher, which is the critical feature of Na incorporation in Ni-promoted MoS2.

Automated summary

This study investigates the effect of Na on Ni-promoted MoS2 during the HDS of dibenzothiophene (DBT), revealing that Na reduces the HDS activity by replacing Ni sites and making the hydrogen dissociation step more endothermic. An increase in Na concentration decreases the HDS of DBT but has a nonmonotonic effect on the selectivity of different mechanistic pathways. Incorporation of Na in Ni-promoted MoS2 enhances the selectivity towards a cost-effective direct desulfurization (DDS) pathway, although the selectivity decreases after reaching an optimal Na concentration.