Effect of Phosphorus Modification on the Acidity, Nanostructure of the Active Phase, and Catalytic Performance of Residue Hydrodenitrogenation Catalysts

A series of NiMoP(x)-Al catalysts with different phosphorus contents were prepared by the incipient wetness co-impregnation method. The effects of phosphorus modification on the acidity, active phase nanostructure, and catalytic properties of the residue hydrodenitrogenation catalysts were investigated to find the role of phosphorus in the catalytic mechanism. The results of temperature-programmed desorption of NH3 and pyridine IR spectroscopy of the catalysts indicate that phosphorus modification can increase the total acid and Bronsted acid. Transmission electron microscopy analysis shows that phosphorus modification increases the stacking number N-A, reduces the slab length L-A of the active MoS2 phase, and increases the Mo dispersion f(mo), leading to the promotion of the sulfidation degree of the active Mo phase and thus increasing the denitrification rate. The catalyst with a 3.4 wt % P2O5 loading shows the highest Bronsted/Lewis acid ratio, the largest amount of three-layer active phases, the smallest L-A, the highest f(mo), the optimal sulfurization degree, and the highest denitrification rate, 63.6%, indicating the correlation between the nanostructure of the active phase and its catalytic property because of the addition of phosphorus.