MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts

Abstract

The most common preparation of high surface area MgO (100–500 m 2 g −1) is calcination of Mg(OH) 2 obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO 3/MgO catalyst is complicated by the high reactivity of MgO to H 2O and MoO 3. During conventional aqueous impregnation, MgO is transformed to Mg(OH) 2, and well soluble MgMoO 4 is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO 3. Mo species of MoO 3/MgO catalyst are dissolved as MgMoO 4 during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al 2O 3-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al 2O 3. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al 2O 3.