Application of <sup>129</sup>Xe NMR Spectroscopy to Analysis of Co-Mo/Al<sub>2</sub>O<sub>3</sub> Hydrodesulfurization Catalyst —Effect of Sulfidation on <sup>129</sup>Xe 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.