QEXAFS study of the sulfidation of ­NiMo/­Al₂O₃ hydrotreating catalysts

Quick-scanning extended X-ray absorption fine structure (QEXAFS) spectroscopy was employed to investigate in situ the sulfidation of Mo and Ni in γ-Al₂O₃-supported hydrotreating catalysts modified with chelating ligands. Mo K-edge QEXAFS enabled the detection of an intermediate product in the sulfidation of Mo. The parameters obtained from the fits of the QEXAFS spectra showed that this product consists of compounds similar to Mo₂S or Mo₃S. QEXAFS also demonstrated that the sulfidation of Ni is strongly influenced by the presence of chelating ligands. Classical EXAFS spectra of the sulfided catalysts showed that Ni forms small sulfided clusters, the size of which is influenced by the presence or absence of the chelating agents.