Application of ¹²⁹Xe NMR Spectroscopy to Analysis of Co-Mo/Al₂O₃ Hydrodesulfurization Catalyst —Effect of Sulfidation on ¹²⁹Xe NMR Spectra—

Abstract

The effect of sulfidation on ¹²⁹Xe NMR spectra of Co-Mo/Al₂O₃ hydrodesulfurization catalysts was investigated. Before sulfidation, catalysts containing cobalt such as Co/Al₂O₃ and Co-Mo/Al₂O₃ showed remarkable ¹²⁹Xe NMR peak broadening, whereas one sharp ¹²⁹Xe NMR peak was observed for Mo/Al₂O₃ and Al₂O₃, mainly caused by the paramagnetic effect of cobalt oxides such as CoAl₂O₄ and CoO. In contrast, after sulfidation, the remarkable broadening of the ¹²⁹Xe NMR peak did not occur. We consider that the paramagnetic effect of cobalt was much reduced due to the transformation of paramagnetic oxides such as CoAl₂O₄ and CoO into antiferromagnetic sulfides such as the Co-Mo-S phase and Co₉S₈. In addition, XPS of the sulfided catalysts showed that the Co 2p binding energy of the sharp peak for Co-Mo/Al₂O₃ was 0.7 eV higher than that for Co/Al₂O₃. This result strongly suggests that cobalt was mainly present as the Co-Mo-S phase on the surface and is closely related to the observation that the ¹²⁹Xe NMR peak of sulfided Co-Mo/Al₂O₃ was shifted further downfield in comparison with sulfided Mo/Al₂O₃. ¹²⁹Xe NMR spectroscopy is sensitive to the formation of the Co-Mo-S phase on Co-Mo/Al₂O₃ hydrodesulfurization catalyst.