Hydrogenolysis and β–elimination mechanisms for C S bond scission of dibenzothiophene on CoMoS edge sites

Alexandre Dumon (1) , Amit Sahu (1, 2) , Pascal Raybaud (1, 2)

1 IFPEN - IFP Energies nouvelles
2 LC - Laboratoire de Chimie - UMR5182

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 Csingle bondS 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.

Mots clés: hydrodesulfurization; dibenzothiophene; hydrogenolysis; beta-elimination; CoMoS; edge sites; density functional theory

Domaines: Chimie; Catalyse

Alexandre Dumon, Amit Sahu, Pascal Raybaud. Hydrogenolysis and β–elimination mechanisms for C S bond scission of dibenzothiophene on CoMoS edge sites. Journal of Catalysis, 2021, 403, pp.32-42. ⟨10.1016/j.jcat.2021.01.030⟩. ⟨hal-03596645⟩