Oxidic precursors of molybdena supported on nickel and magnesium aluminate hydrotreating catalysts

The oxidic precursors of molybdena-based hydrotreating catalysts have been prepared using nickel and magnesium aluminates and characterized by laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). Three series of supports (80, 120 and 140 m².g^?1) have been investigated. Their aluminate spinel structure was confirmed both by X-ray diffraction (XRD) and LRS. Nickel oxide and magnesia have also been detected on the low surface area systems. In both series, a surface deficit of the foreign cation has been observed relative to the Al³⁺ of the aluminate phase. This deficit was more pronounced for Ni²⁺. Deposition of molybdate species does not modify the surface composition of these supports and a monolayer-like coverage up to 4.5 to 5 Mo at.nm^?2 was obtained. Nickel added by impregnation was shown to interact with the supported oxomolybdate species, whereas the nickel of the support does not. These investigated supports closely resemble γ --- Al₂O₃ in the preparation of hydrotreating catalysts.