Effect of Diethylene Glycol on the Formation of the Oxide Precursor of the Nickel–Molybdenum Hydrotreating Catalyst

The effect of diethylene glycol addition on the formation of oxide precursors of nickel–molybdenum sulfide hydrotreating catalysts was studied by Raman spectroscopy and differential dissolution. The NiMoP/Al 2 O 3 catalyst was prepared by impregnation of γ-alumina with an aqueous solution obtained by successive dissolution of H 3 PO 4 , MoO 3 , and Ni(OH) 2 in water. To prepare the NiMoP-diethylene glycol/Al 2 O 3 catalyst, diethylene glycol was added to the impregnation solution. On contact of the impregnation solution with γ-alumina, the H x P 2 Mo 5 O 23 (6− x )− heteropolyanions initially present in the solution decompose to form polymolybdates. Without organic additive, the heptamolybdate anion (Mo 7 O 24 6− ) is formed, whereas the use of diethylene glycol leads to the formation of polymolybdates of different structures, mainly with high degree of polymerization. In contrast to Mo 7 O 24 6− , such polymolybdates are probably incapable of interacting with the support surface to generate aluminum molybdates that do not form the most active “NiMoS” phase.