Molybdenum sulfide clusters

Hydrodesulfurization of Benzothiophene Catalyzed by Molybdenum Sulfide Cluster Encapsulated into Zeolites... 

A cationic molybdenum sulfide cluster [Mo3S4(H20)9] " with incomplete cubane-type structure and a cationic nickel-molybdenum mixed sulfide cluster [Mo3NiS4Cl(H20)9p " with complete cubane-type structure were introduced into zeolites NaY, HUSY and KL by ion exchange. Stoichiometry of the ion exchange was well established by elemental analyses. The UV-visible spectra and EXAFS analysis data exhibited that the structure of the molybdenum cluster remained virtually intact after ion exchange. MoNi/NaY catalyst prepared using the molybdenum-nickel sulfide cluster was found to be active and selective for benzothiophene hydrodesulfurization. 

Structure Control of Molybdenum Sulfide Clusters Encaged in Zeolite Prepared by a CVD Technique... 

Intrazeolite molybdenum sulfide catalysts (MoSx/NaY) were prepared by a CVD technique using Mo(CO)6. On the basis of the Mo-Mo atomic distance, it has been shown that a MoSs-like molybdenum sulfide dimer clusters are formed when the Si/Al ratio is between 3.5 and 2.4. When the Si/Al ratio was very high, finely dispersed M0S2 particles were formed. The specific activity of molybdenum sulfide clusters for the HDS of thiophene decreased as the Mo-Mo atomic distance increased. It has been substantiated that the morphology, structure, and catalytic activity of intrazeolite molybdenum sulfides are controlled by the host zeolite composition. 

Hexacarbonyl molybdenum Mo(CO)6 was successfully used to prepare intrazeolite molybdenum sulfide clusters in the cavities of NaY (CVD technique) [4,5,7,8]. The decomposition and sulfidation of Mo(CO)e encaged in NaY were extensively studied by Okamoto et al. [7-11] by means of temperature programmed decomposition (TPDE), XPS, and XAFS techniques. It has been claimed that the structure of molybdenum sulfides is described as molybdenum dinuclear sulfide clusters M02S4. de Bont et al. [12] supported the formation of molybdenum sulfide dimer species. The extremely high dispersion of molybdenum sulfide clusters prepared fi"om Mo(CO)6 was also suggested by an NO adsorption capacity much hi er than those of other conventional catalyst systems such as M0S2/AI2O3 [9]. 

In this present study, we prepared molybdenum sulfide clusters encaged in a series of NaY zeolites with different Si/Al ratios. It is shown here that the local structure of molybdenum sulfide clusters and their intrinsic activity are finely controlled by the zeolite composition. 

Structure control of molybdenum sulfide clusters encaged in zeolite... 

With MoSx/USY-Na(3.5) and MoSx/NaY(2.8), the coordination number of Mo-Mo is very close to unity (Table 2), suggesting the formation of extremely dispersed molybdenum sulfide clusters, possibly Mo dimer species in line with previous studies [10-13]. The Mo-Mo atomic distance of the cluster is... 

The location of molybdenum sulfide clusters and M0S2 particles was estimated on the basis of the pore volume of MoSx/zeolite, which was measured by benzene adsorption. Table 3 summarizes the pore volumes of the zeolite before and after the incorporation of molybdenum sulfide clusters. The pore volume of the NaY zeolite is about 0.30 cm g and consistent with the crystallographically calculated volume (0.30 cm g ) of the supercage of NaY zeolite. The pore volumes of USY-Na(3.5) and NaY(630) were slightly lower compared with that of NaY, suggesting a partial destruction of the zeolite framework during dealumination processes. 

The pore volumes of the zeolite were decreased by the introduction of molybdenum sulfide clusters, the extent of decrease being 0.1 cm g for the NaY and USY-Na zeolites. This substantiates the incorporation of molybdenum... 

In the present study, we have shown that the morphology (dimer clusters or finely dispersed M0S2 particles), structure (Mo-Mo atomic distance), and catalytic activity (the HDS of thiophene) of molybdenum sulfide clusters encaged in NaY zeolite can be controlled by the factors such as the host zeolite composition (Si/Al ratio) through Mo-Oz interactions. 

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