Correlation between hydrodesulfurization activity and order of Ni and Mo sulfidation in planar silica-supported NiMo catalysts: The influence of chelating agents

Surface science models of silica-supported NiMo catalysts have been prepare d to study the formation of the active phase ("NiMoS") in hydrotreating cat alysts. Combination of XPS and thiophene hydrodesulfurization (HDS) measure ments shows that the key step in the formation of the NiMoS phase is the or der in which Ni and Mo precursors transfer to the sulfidic state. In NiMo s ystems prepared by conventional methods the sulfidation of Ni precedes that of Mo. However, complexing Ni to chelating agents like nitrilotriacetic ac id, ethylenediamine, ethylenediaminetetraacetic acid (EDTA), and 1,2-cycloh exanediaminetetraacetic acid (CyDTA) retard the sulfidation of Ni. For EDTA and CyDTA the Ni sulfidation is delayed to temperatures where MoS2 is alre ady formed. These catalysts show the highest activity in thiophene HDS, ind icating that complete sulfidation of Mo preceding that of Ni provides the i deal circumstances for NiMoS formation. (C) 2001 Academic Press