Effects of support on hydrodenitrogenation activity of nickel phosphide catalysts

The effects of the support on active site formation and hydrodenitrogenation (HDN) activity of nickel phosphide catalysts were examined, using TiO2, Al2O3 and TiO2-Al2O3, composite supports. A series of TiO2-Al2O3 prepared by hydrolysis and deposition of tetrabutyl titanate on macropore Al2O3, and the supported nickel phosphide catalyst, were prepared by incipient wetness impregnation and in situ H2 reduction method. The samples were characterized by X-ray diffraction (XRD), BET surface area, transmission electron microscopy (TEM) and H2 temperature-programmed reduction (H2-TPR).Their hydrodenitrogenation (HDN) performance were evaluated on a continuous-flow fixed-bed reactor by using quinoline as the model molecules. The results showed that the TiO2-Al2O3 composite support still retained the pore properties of macropore Al2O3, and TiO2 were well dispersed on the Al2O3 surface in the form of anatase. Different supports have great influence on the reduction behaviour of the oxidic precusors and HDN activity of phosphide catalysts. The main active phase after reduction was Ni2P phase for the TiO2 and TiO2-Al2O3 supportd catalyst, but only Ni12P5 appeared for the Al2O3 supported catalyst. The order of HDN activities of nickel phosphide reduced at optimal reaction conditions was TiO2-Al2O3 > Al2O3> TiO2. TiO2-Al2O3 supported catalyst with the Ti /Al atomic ratio of 1:8 exhibited the highest HDN activity among all catalysts. The presence of TiO2 weakened the strong interaction between the Al2O3 and phosphate, and contributed to the formation of Ni2P active phase and the improvement of HDN activity.