Effect of phosphorus modification on the catalytic properties of Mo-Ni/Al₂O₃ in the hydrodenitrogenation of coal tar

Mo-Ni/Al₂O₃ catalysts were modified with phosphorus by using the impregnation method. By changing the addition sequence of phosphorus, three types of catalysts, viz. MoP-Ni/Al₂O₃, Mo-NiP/Al₂O₃ and Mo-Ni/PAl₂O₃, were obtained with a P loading of 1.34%. These catalysts were characterized by X-ray diffraction, temperature-programmed desorption of NH₃, temperature-programmed reduction by H₂ and N₂ sorption experiment. The catalytic properties of these catalysts were investigated with the hydrodenitrogenation (HDN) of low- and middle-temperature coal tar obtained from Xinjiang province. It was shown that appropriate P addition sequence can alter acid site distributions, increase the proportion of effective pores between 10 and 13 nm, weaken the interaction of the support and active metal components and make the reduction of the active components easier, consequently, improving the catalytic performance. The HDN activity of the three types of catalysts decreased in the order of Mo-Ni/PAl₂O₃(74.36%) > Mo-NiP/Al₂O₃(72.74%) > Mo-Ni/Al₂O₃(56.13%) > MoP-Ni/Al₂O₃(71.72%).