The effect of phosphate on the hydrodenitrogenation activity and selectivity of alumina-supported sulfide Mo, Ni, and Ni-Mo catalysts

Al2O3–supported Mo, Ni and Ni–Mo catalysts were prepared via pore volume impregnation of the support with aqueous solutions of H3PO4, (NH4)6Mo7O24 and Ni(NO3)2. The catalysts were sulfided in situ and tested in the hydrodenitrogenation (HDN) of quinoline (643 K, 3.0 MPa) and the hydrodesulfurisation (HDS) of thiophene (673 K, 0.1 MPa) and were further characterized by X–ray photoelectron spectroscopy (XPS). The Ni/Al2O3 and Mo/Al2O3 catalysts had very low quinoline conversions to hydrocarbons which changed somewhat in the presence of phosphate. For the Ni–Mo catalysts the addition of phosphate resulted in an increased quinoline conversion to hydrocarbons and an increased selectivity for unsaturated N–free hydrocarbons. The effect of phosphate on the HDN activity and selectivity did not correlate with its effect on the dispersion of Ni or Mo as determined by XPS. Moreover the HDS activity was not influenced by the presence of phosphate. This indicates that the addition of phosphate does not lead to an increase in the formation of the active "Ni–Mo–S" metal sulfide sites but rather to the formation of a new type of HDN site which is associated with phosphate.