129Xe NMR (nuclear magnetic resonance), a useful analytical tool for the investigation of zeolite pores, was evaluated as a novel technique for the analysis of active sites on Mo/Al
2O
3 hydrodesulfurization catalyst.
129Xe NMR spectroscopy of Mo/Al
2O
3 catalyst detected a single peak attributed to xenon migrating in a few micropores on the surface of Al
2O
3. When a chemical shift δ of the peak was plotted against the amount of adsorbed xenon
N in the NMR measurement, a nonlinear variation of δ appeared for sulfided Mo/Al
2O
3 catalyst. This result indicates that xenon strongly interacts electronically with molybdenum species on the surface. In addition, the term δ
0 was calculated which mainly depends on collisions between xenon and the catalyst surface from the fitting of the plot to a theoretical equation. As a result, δ
0 became larger with increased the molybdenum content. This result shows that migration of xenon was inhibited by molybdenum species on the surface. Increase in the sulfurization temperature also caused δ
0 to increase and almost corresponded to the sulfurization degree of molybdenum measured by XPS (X-ray photoelectron spectroscopy). This indicates that δ
0 is sensitive to formation of MoS
2 crystallites on the surface.
129Xe NMR can be a powerful tool for analysis of the formation of MoS
2 crystallites on Mo/Al
2O
3 catalyst.
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