New insights on the role of H2S and sulfur vacancies on dibenzothiophene hydrodesulfurization over MoS2 edges.

Graphical abstract Highlights • Sulfur coverage at the edge of MoS 2 influences the effect of H 2 S on HDS activity. • Synergy of hematite and MoS 2 leads to favored DDS pathway. • The sigma adsorption of DBT is favored with vacancies present at edges of MoS 2. • Iron synergy with MoS 2 leads to the formation of a vacancy site over Mo-edge. • Acid sites are produced more readily by H 2 S dissociation than their H 2 counterparts. Abstract Experimental and computational studies were performed to investigate the effect of varying sulfur coverage over MoS 2 in hydrodesulfurization (HDS) of dibenzothiophene (DBT). Hematite and iron particles were employed as H 2 S scavengers. MoS 2 showed high hydrogenation (HYD) preference in HDS of DBT which was explained by the DFT calculations showing that HYD pathway is more favorable in brim adsorption. The addition of hematite drastically shifted this preference to direct desulfurization (DDS) pathway. DFT calculations showed that MoS 2 forms edges with 25% sulfur coverage in presence of hematite. The hydrogen dissociation was found to be energetically unfavorable (deactivated) over the Mo-edge with such sulfur coverage and becomes exothermic (reactivated) only after sigma adsorption of DBT on a vacancy site. In agreement with experimental results, calculations also showed that in the presence of vacancies, the sigma adsorption of DBT and therefore DDS pathway is more favorable. MoS 2 with iron particles present, favored the HYD reaction route, however, compared to MoS 2 the biphenyl (BP) selectivity increased while the selectivity for isomerized products was reduced. DFT calculations showed that in the presence of iron, Mo-edge has 37% coverage with a vacancy site formed over this edge which explains the higher DDS activity for this catalyst compared to MoS 2. A difference was observed in the ability of H 2 and H 2 S in creation of acid sites upon their dissociation at the edges. This was attributed to the difference in S H bond energies in each molecule and the change in oxidation sate of neighboring Mo atoms. [ABSTRACT FROM AUTHOR]