Silica-Alumina Based Nickel-Molybdenum Catalysts for Vacuum Gas Oil Hydrocracking Aimed at a Higher Diesel Fraction Yield

Nickel-molybdenum hydrocracking catalysts based on amorphous silica-aluminas (ASAs) with Si/Al = 0.3-1.5 have been prepared using chemicals and methods available for catalyst plants. The acidic properties of the ASA surface have been investigated by IR spectroscopy of adsorbed CO, and it has been demonstrated that the Si/Al ratio has an effect on the concentration and strength of Bronsted and Lewis acid sites in the ASA. The catalysts have been characterized by low-temperature nitrogen adsorption and transmission electron microscopy, and it was found that the Si/Al ratio in the ASA has a considerable effect on the textural properties of the catalysts and only a slight effect on the particle size of the sulfide active component. The catalysts have been tested in vacuum gas oil hydrocracking in a laboratory-scale high-pressure flow reactor under typical industrial hydrocracking conditions. The highest diesel fraction yield (>60 wt % at 400 degrees C) has been obtained with the catalyst based on the Si/Al = 0.9 ASA, which has the strongest Bronsted acid sites. With the catalysts based on the Si/Al = 0.3 and 1.5 ASAs, the diesel fraction yield is much lower. This may be due to the lower concentration and strength of acid sites in these catalysts and their smaller specific surface area. The NiMo catalyst based on Si/Al approximate to 0.9 ASA is recommended for industrial use in refineries aimed at obtaining the maximum possible yield of low-sulfur, high-cetane, diesel fuels.