Effect of phosphorus content on the active phase structure of NiMo/Al₂O₃ catalyst

NiMoP/Al₂O₃ catalysts with different phosphorus contents were prepared by co-impregnation method and characterized by temperature-programmed reduction (TPR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) tests. The effect of phosphorus content on the active phase structure of these catalysts was investigated. The TPR results indicated that with the increase of the phosphorus content in the catalysts, the amount of tetrahedral Mo species was decreased, while that of octahedral Mo species was increased. The HRTEM results showed that the number of stacking layers of MoS₂ nanoparticles increased with the phosphorus content, which was effective to enhance the hydrogenation selectivity of the catalysts. The fraction of available Mo dispersion (fMo) and the number of active phases in the catalysts increased with increasing phosphorus content to P/MoO₃ = 0.09; beyond that, a reverse trend was observed. High HDS and HDN activity were obtained over the catalyst with the phosphorus content of P/MoO₃ = 0.09, which could be attributed to its high concentration of Mo atoms on the catalyst surface, high efficient promotion rate (PR) and high promoter ratio (Ni/Mo). However, excessive phosphorus content may deteriorate the performance of NiMoP/Al₂O₃ catalysts due to the aggregation of active components.