Optimum coating of USY as a support component of NiMoS on alumina for deep HDS of gas oil Original Research Article

Four types of alumina and/or USY-zeolite-supported NiMo catalysts (NMA, NMAZ, NMACZ1, NMACZ2) were examined in an autoclave for HDS of straight run gas oil (SRGO; S = 11,780 ppm) and its hydrodesulfurized gas oils (HSRGO; S = 340 ppm) to simulate a first and second layer catalyst. NMACZ1 and NMACZ2 were physical mixtures of alumina and surface modified USY-zeolites with different amounts of alumina, while NMAZ is a physical mixture of alumina and USY-zeolite. ACZ series catalysts were prepared to obtain high HDS activity of NiMo on zeolite-containing supports without extensive cracking of hydrocarbons. USY-zeolite in NMACZ1 was coated with more alumina than that in NMACZ2, which showed the highest HDS activity in the first and second layers, achieving 34 ppm sulfur (ppm S) for the first layer and almost complete removal of sulfur species in the second layer at 340 °C. NMAZ showed high HDS activity for both layers. NMACZ1 showed medium HDS activity for the first layer, but very high HDS activity for refractory sulfur species in the second layer. A large amount of light hydrocarbons were produced over NMAZ through cracking of heavy hydrocatbon, while NMACZ1 and NMACZ2 produced lower amounts of light hydrocarbons, reflecting the greater amount of coating alumina. It must be noted that lower reaction temperatures of 330 and 320 °C achieved almost completely 0 ppm in the second layer, where the hydrocracking was very low level. Their clearly defined HDS activities against each layer may be due to the differences of MoS2 structures, support acidities and their surface areas, which are in turn due to morphologies of their supports.