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In this work, we have used transmission electron microscopy (TEM) to study Co 6 S 8 (PPh 3 ) xpillared MoS 2 and have directly observed that the Co clusters can either intercalate into the bulk or can bind to defect sites at the edges of MoS 2 . A distribution of discrete 0.87 nm scattering centers has been assigned to remnants of the Co 6 S 8 (PPh 3 ) 6 clusters. On the basis of X-ray diffraction (XRD) studies, a lattice expansion of 1.48 nm was expected if the triphenylphosphine ligands remained intact. The distribution of Co scattering centers, however, was consistent with that expected for a Co 6 S 8 core (0.8 nm). The expansion of the {00l}-MoS 2 planes was almost always localized about a single Co cluster, and the degree of lattice expansion (0.78 nm) was also consistent with the dimensions of the Co 6 S 8 cores, confirming that the ligands had been nearly completely removed. The organic ligands were removed either during the vacuum pumpdown in the TEM specimen chamber or almost immediately upon electron-beam exposure. Additional electron-beam exposures of up to 1 h caused no further structural changes. The inorganic framework remained intact throughout the duration of the experiment. The Co 6 S 8 -pillared MoS 2 materials possessed dibenzothiophene (DBT) hydrodesulfurization (HDS) activities that were slightly better than that of a commercial sulfided Co-Mo/Al 2 O 3 catalyst under low-severity HDS conditions. However, the selectivity to biphenyl was somewhat poorer than that of commercial Co-Mo and Ni-Mo catalysts under all conditions examined. The HDS and TEM results suggest that the role of Co in sulfided Co-Mo catalysts is to prop apart MoS 2 layers, creating a higher percentage of "rim" sites (in the Daage-Chianelli terminology) and enhancing hydrogenation capability.

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