Microstructural characterization of highly HDS-active Co{sub 6}S{sub 8-}pillared molybdenum sulfide.
In this work, we have used transmission electron microscopy (TEM) to study Co{sub 6}S{sub 8}(PPh{sub 3}){sub x}-pillared MoS2 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{sub 2}. A distribution of discrete 0.87 nm scattering centers has been assigned to remnants of the Co{sub 6}S{sub 8}(PPh{sub 3}){sub 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{sub 6}S{sub 8} core (0.8 nm). The expansion of the {l_brace}00l{r_brace}-MoS{sub 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{sub 6}S{sub 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{sub 6}S{sub 8}-pillared MoS{sub 2} materials possessed dibenzothiophene (DBT) hydrodesulfurization (HDS) activities that were slightly better than that of a commercial sulfided Co-Mo/Al{sub 2}O{sub 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{sub 2} layers, creating a higher percentage of 'rim' sites (in the Daage-Chianelli terminology) and enhancing hydrogenation capability.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- ER
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 937832
- Report Number(s):
- ANL/CHM/JA-21506; CMATEX; TRN: US200905%%552
- Journal Information:
- Chem. Mater., Vol. 10, Issue 1998; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- ENGLISH
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