Catalytic performance of NiMo/Al₂O₃-USY in the hydrocracking of low-temperature coal tar

A series of NiMo/Al₂O₃-USY catalysts with different MoO₃ contents were prepared through incipient wetness method and further modified with NH₄F. The NiMo/Al₂O₃-USY catalysts were characterized by XRD, XPS, HR-TEM, NH₃-TPD, H₂-TPR and N₂ adsorption and their catalytic performance in the hydrocracking of low-temperature coal tar (LTCT) was investigated in a 200 mL fixed-bed reactor. The results indicate that the appropriate MoO₃ content is 15% (mass ratio); higher MoO₃ content may lead to the agglomeration of active metals on the support, although it has little influence on the sulfidation degree of Mo species and the conversion of coal tar upon hydrocracking. In addition, the amount of strong acid sites and pore diameter decrease gradually with a further increase in the MoO₃ content, which is disadvantageous for deep hydrocracking. The modification of USY zeolite with NH₄F solution can enlarge the average pore diameter of resultant NiMo/Al₂O₃-USY catalysts and then improve the residue conversion of coal tar. However, the amount of strong acid sites decreases obviously when the concentration of NH₄F solution exceeds 0.6 mol/L, which may lead to an increase of the sulfur content in the hydrocracking product. Over the NiMo/Al₂O₃-USY catalyst modified with 0.6 mol/L NH₄F solution, the residue conversion of coal tar reaches 87.65%; the sulfur contents in the gasoline fraction (< 180 ℃) and diesel fraction (180-320 ℃) are 5.96 and 34.98 mg/kg, respectively.