Effect of preparation methods on the hydrocracking performance of NiMo/Al2O3 catalysts

In this work, NiMo catalysts with various contents of MoO3 were prepared through incipient wetness impregnation by a two-step method (NM-xA) and one-pot method (NM-xB). The catalysts were then characterized by XRD, XPS, NH3-TPD, H2-TPR, HR-TEM, and N2 adsorption–desorption technologies. The performance of the NiMo/Al2O3 catalysts was investigated by hydrocracking low-temperature coal tar. When the MoO3 content was 15 wt％, the interaction between Ni species and Al2O3 on the NM-15B catalyst was stronger than that on the NM-15A catalyst, resulting in the poor performance of the former. When the MoO3 content was 20 wt％, MoO3 agglomerated on the surface of the NM-20A catalyst, leading to decreased number of active sites and specific surface area and reduced catalytic performance. The increase in the number of MoS2 stack layers strengthened the interaction between Ni and Mo species of the NM-20B catalyst and consequently improved its catalytic performance. When the MoO3 content reached 25 wt％, the active metals agglomerated on the surface of the NiMo catalysts, thereby directly decreasing the number of active sites. In conclusion, the two-step method is suitable for preparing cat-alysts with large pore diameter and low MoO3 content loading, and the one-pot method is more appro-priate for preparing catalysts with large specific surface area and high MoO3 content. Moreover, the NM-xA catalysts had larger average pore diameter than the NM-xB catalysts and exhibited improved desul-furization performance.