Selective hydrogenation of dienes to olefins and sulfur removal from model FCC gasoline over Ni-Mo sulfide catalyst supported on MCM-41 type silica

Abstract

The transformation of 2,5-dimethyl-hexadiene-2,4 and benzothiophene over mesoporous MCM-41 silica supported Ni-Mo sulfide catalyst was estimated. The physico-chemical properties of support and catalyst were evaluated by XRD, low-temperature N₂ adsorption, TEM, EDX mapping and XPS analysis. The catalyst reveals the sulfide particles with 5.4 nm in length and 3.5 stacks supported on MCM-41 silica having hexagonal porous arrangement with 2.5 nm in diameter. The effective content of Mo in MoS₂ was 48.3 wt%. According to thermodynamic calculations, the equilibrium mixture contains 2,5-dimethylhexane (82 %) and n-octane (18 %). For catalytic tests, at 260–340 °C for 1–2 h selectivity to olefins reaches 85–90 %, whereas 100 % benzothiophene conversion to ethylbenzene was achieved at 300–340 °C for 6–10 h. n-Octane was detected as the product of skeletal isomerization of 2,5-dimethyl-hexadiene-1,5. For model FCC gasoline, the optimal conditions providing effective sulfur removal and selective hydrogenation were defined as 300–320 °C and 2–4 h under 3–5 MPa hydrogen pressure. The reusability of the catalyst was evaluated using model feed containing BT and C₈H₁₄ with molar ratio of 2:1 under 5 MPa hydrogen pressure at 320 °C for 2 h without any pre-treatment or regeneration of the catalyst before the next reaction run. In was established that HDS/HYDO selectivity increases with reaction run, which is due to the conversion of C₈H₁₄ decrease more significant as compared to that for BT, whereas conversion and product distribution maintain unchanged from 5 reaction run, indicating that the catalyst is running-in. For the spent NiMoS/MCM-41 catalyst the effective content of Mo in MoS₂ phase reaches 42.8 wt%, whereas that for Ni in NiS and NiMoS phase was 1.7 wt% and 0.7 wt%, respectively, which is compared to those values for the fresh sample.