LAUSR

Abstract Unraveling the mechanisms of hydrodesulfurization (HDS) of dibenzothiophene (DBT) and the corresponding active sites represents a scientific challenge to improve the intrinsic performances of Co-promoted MoS2 (CoMoS) catalysts. By using density functional theory calculations, we compare two historical mechanisms for the C S bond scission of DBT (direct desulfurization): direct hydrogenolysis of DBT and β–elimination of α,β–dihydro-diobenzothiophene (α,β–DHDBT) on four relevant sites of the two CoMoS M- and S-edges. On the Co promoted M-edge, the α,β–DHDBT is formed through dihydrogenation which is kinetically competing with hydrogenolysis (both exhibiting activation free energies, ΔG‡, smaller than +1.24 eV). On the S-edge, both dihydrogenation and hydrogenolysis exhibit higher ΔG‡ (>+1.78 eV). Interestingly, on the S-edge, the β–elimination (E2 type) on the α,β–DHDBT is found to be kinetically competing (ΔG‡ = +1.14 eV). The elimination of Hβ atom involves a S2 dimer close to the S-vacancy site where DHDBT is adsorbed. Since this leaving Hβ atom is distinct from the one added at dihydrogenation step, this may explain why direct desulfurization of 4,6-alkyl substituted DBT compounds is hampered according to the elimination mechanism. We finally discuss the possible synergy between the two edges of CoMoS for HDS of DBT.