Microstructural Characterization of Highly HDS-Active Co6S8-Pillared Molybdenum Sulfides

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• 作者：James Brenner ; Christopher L. Marshall ; Leroy Ellis ; Nancy Tomczyk ; Joy Heising ; and Mercouri Kanatzidis
• 刊名：Chemistry of Materials
• 出版年：1998
• 出版时间：May 1998
• 年：1998
• 卷：10
• 期：5
• 页码：1244 - 1257
• 全文大小：455K
• 年卷期：v.10,no.5(May 1998)
• ISSN：1520-5002

文摘

In this work, we have used transmission electron microscopy (TEM)to studyCo₆S₈(PPh₃)_x-pillared MoS₂ and have directly observed that the Coclusters can either intercalate intothe bulk or can bind to defect sites at the edges of MoS₂.A distribution of discrete 0.87 nmscattering centers has been assigned to remnants of theCo₆S₈(PPh₃)₆clusters. On the basisof X-ray diffraction (XRD) studies, a lattice expansion of 1.48 nm wasexpected if thetriphenylphosphine ligands remained intact. The distribution of Coscattering centers,however, was consistent with that expected for aCo₆S₈ core (0.8 nm). The expansion ofthe{00l}-MoS₂ planes was almost alwayslocalized about a single Co cluster, and the degree oflattice expansion (0.78 nm) was also consistent with the dimensions ofthe Co₆S₈ cores,confirming that the ligands had been nearly completely removed.The organic ligands wereremoved either during the vacuum pumpdown in the TEM specimen chamberor almostimmediately upon electron-beam exposure. Additional electron-beamexposures of up to 1h caused no further structural changes. The inorganic frameworkremained intactthroughout the duration of the experiment. TheCo₆S₈-pillared MoS₂ materialspossesseddibenzothiophene (DBT) hydrodesulfurization (HDS) activities that wereslightly better thanthat of a commercial sulfided Co-Mo/Al₂O₃catalyst under low-severity HDS conditions.However, the selectivity to biphenyl was somewhat poorer than thatof commercial Co-Moand Ni-Mo catalysts under all conditions examined. The HDS andTEM results suggestthat the role of Co in sulfided Co-Mo catalysts is to prop apartMoS₂ layers, creating ahigher percentage of "rim" sites (in the Daage-Chianelliterminology) and enhancinghydrogenation capability.