TiO₂-SiO₂ supported hydrotreating catalysts: physico-chemical characterization and activities

Abstract

Hydrotreating of model molecules over high specific surface area (SSA) Co(Ni)Mo/TiO₂-SiO₂ mixed oxide supported catalysts has been investigated in a micro-catalytic reactor at 400°C and atmospheric pressure. Activity studies are carried out for thiophene hydrodesulfurization (HDS) and 1-cyclohexene hydrogenation (HYD). The effect of support composition, molybdenum content (2-14 wt.% Mo) and promoters contents (1-5 wt.% Co or Ni) is examined. Supported catalysts are characterized by BET specific surface area, X-ray diffraction (XRD), pore volume, zero point charge (ZPC) and low temperature oxygen chemisorptions (LTOC). Sulfided catalysts showed wide range of activity variation with support composition which relishes that molybdenum sulfided active phases strongly depend on the nature and composition of support. LTOC and catalytic activity results showed similar trend with the effect of molybdenum variation indicating that the number of anion vacancies varies with variation of MoS₂ phases. The highest activities were observed at 8 wt.% Mo loading and after that activity decreases with decreasing the anionic vacancies. The characterization results of XRD, ZPC and LTOC are well agreed about the Mo monolayer formation. Incorporation of TiO₂ with SiO₂ alters the nature of weak interaction of active phases with SiO₂ support, and overcome it through poor dispersion on the support surface. Therefore, TiO₂ counterpart plays a role to provide high intrinsic activity and generate favorable morphology of MoS₂ phases and metal support interaction.