The influence of chelating ligands on the sulfidation of Ni and Mo in NiMo/SiO{sub 2} hydrotreating catalysts
- Eidgenoessische Technische Hochschule, Zuerich (Switzerland)
The influence of the addition of chelating ligands like nitrilotriacetic acid (NTA) during the preparation of NiMo/SiO{sub 2} hydrotreating catalysts on catalyst activity and structure was studied by means of thiophene HDS (hydrodesulfurisation) activity measurements, temperature programmed sulfidation, and EXAFS (extended X-ray absorption fine structure) spectroscopy. The HDS activities of dried NiMo/SiO{sub 2} catalysts prepared in the presence of NTA were much higher than those prepared by classic pore volume impregnation in the absence of NTA. Calcination led to sintering of the MoO{sub 3} on the SiO{sub 2} support, and thus to low HDS activities of the corresponding sulfided catalysts. After sulfidation 493 K of dried but not calcined catalysts, molybdenum was fully sulfided, but not to MoS{sub 2}. The observed Mo-S and Mo-Mo distances pointed to Mo(V)-S{sub 2}-Mo(V) or Mo(IV)-S{sub 2}-Mo(IV) structures. MoS{sub 2} was formed after sulfidation at 673 K, and its dispersion was independent of the presence of NTA in the original oxidic catalyst precursors. However, NTA had a dramatic influence on the sulfidation behavior of Ni. In the presence of NTA, Ni was sulfided between 493 and 583 K, while in its absence sulfidation started at temperatures below 493 K. It is proposed that the sulfidation of Ni at a relatively low temperature, before MoS{sub 2} crystallites are formed, enhances the formation of thermodynamically stable nickel sulfides so that less of the HDS-active, but metastable, NiMoS phase can be formed. The role of NTA and similar chelating ligands is to prevent the sulfidation of nickel at low temperature, and thus increase the formation of the NiMoS phase. 38 refs., 10 figs., 3 tabs.
- OSTI ID:
- 508457
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 163; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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