Contrast activities of four alumina and alumina-silica-supported nickel-molybdenum sulfide catalysts for deep desulfurization of gas oils

Four NiMoS catalysts on conventional alumina (NMA-1), acidified alumina (NMA-2), and on two alumina-silica mixtures of different preparation procedures with 70% (NMASA1-70) and 50% (NMASA2-50) silica supports were prepared. In HDS and HDN of straight run gas oil (SRGO) and its desulfurized oil (HSRGO), their selective activities toward above reactions were compared since the best combination of two catalysts in two-layer bed was expected to achieve deep HDS of SRGO rather easily. NMA-1 removed reactive sulfur species effectively and refractory sulfur species moderately but failed to remove nitrogen species in SRGO. The catalyst was not effective to remove refractory sulfur species in HSRGO to achieve the total sulfur level of less than 10 ppm S in the second layer. NiMoS on acidified alumina (NMA-2) and NMASA1-70 removed nitrogen species very effectively but sulfur species in SRGO were not so efficiently removed. Both catalysts were very active for HSRGO to attain 10 ppm sulfur level. Rapid HDN in SRGO over the catalysts appears to retard HDS of SRGO, leaving even reactive sulfur species unreacted. Among the catalysts, NiMoASA2-50 was very active for all reactions to achieve less than 10 ppm from SRGO via two stages. The rapid HDN over the particular catalyst allowed the effective HDS after the rapid completion of HDN. Such contrast activities of four catalysts are compared as regards their surface area, acidity and NiMoS location on the support particles. NiMo on alumina or on the border of acidified alumina and silica of right content is most activated for HDN as well as HDS. Acidity appears essential for HDN. Larger surface area of the particular alumina-silica support is certainly favorable for both HDS and HDN. The larger content of silica in NMASA1-70 may not be favorable for high dispersion of NiMoS to show higher activity for HDS while HDN progresses.