Sulfide structures, zeolite-like

Catalysts may be metals, oxides, zeolites, sulfides, carbides, organometallic complexes, enzymes, etc. The principal properties of a catalyst are its activity, selectivity, and stability. Chemical promoters may be added to optimize the quality of a catalyst, while structural promoters improve the mechanical properties and stabilize the particles against sintering. As a result, catalysts may be quite complex. Moreover, the state of the catalytic surface often depends on the conditions under which it is used. Spectroscopy, microscopy, diffraction and reaction techniques offer tools to investigate what the active catalyst looks like. 

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. 

Fig. 15. Left Proposed cubane-like structure of a Cd4S4 cluster anchored with two site II Cd + cations within the supercage of zeolite Y. Hatched circles represent cadmium cations, open circles represent sulfide anions. Right Schematic depiction of an ideal diamond superlattice of Cd2(Cd4S4) clusters in the supercage of a zeolite Y host, after [252,305]...

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