EXAFS studies on the local structure of Ni and Mo in nickel-molybdenum catalyst system

The local structure surrounding Mo and Ni atoms in a series of nickel-molybdenum-γ-Al₂O₃ catalysts promoted by P₂O₅ or TiQ₂ was investigated using EXAFS technique at Mo and Ni 1s edge. The analysis results show that the addition of P or Ti increases the metal dispersion under the condition of high Mo content and the octahedral structure in MoNiP catalysts is more abundant than that in MoNiTi. Moderate content of P₂O₅ facilitates the formation of the octahedral structure. It is also found that oxygen atoms of Mo-O bond in octahedral structure are easy to be substituted by S in hydrodesulphurization(HDS) reaction. In MoNiP catalysts the higher HDS activity might be caused by the abundance of octahedral structure.