Cobalt-molybdenum catalysts, role

The sulfidation mechanisms of cobalt- or nickel-promoted molybdenum catalysts are not yet known in the same detail as that of M0O3, but are not expected to be much different, as TPS patterns of Co-Mo/A1203 and Mo/Al203 are rather similar [56J. However, interactions of the promoter elements with the alumina support play an important role in the ease with which Ni and Co convert to the sulfidic state. We come back to this after we have discussed the active phase for the hydrodesulfurization reaction in more detail. 

The Role of Promoter Atoms in Cobalt-Molybdenum and Nickel-Molybdenum Catalysts... 

Some remarks must be made about the role of oxygen coordination. Several authors have remarked that the coordination in catalytic oxides is of major importance. Mitchell and Trifiro (e.g. ref. 219) concluded that a bismuth molybdate catalyst is most active if the amount of tetrahedrally coordinated molybdenum is large in comparison with octahedrally coordinated molybdenum. However, V205 and Sb2Os are structures with specific octahedral coordination [142] and often the coordination is changed by reduction of the catalyst or by the support [203]. In a- and /3-cobalt molybdates the coordination differs, but the catalytic behaviour is really the same. The low temperature Bi2Mo06 (7 phase) has an octahedral coordination but is an effective catalyst. 

In addition to being important in industry, transition metal ions play a vital role in living organisms. For example, complexes of iron provide for the transport and storage of oxygen, molybdenum and iron compounds are catalysts in nitrogen fixation, zinc is found in more than 150 biomolecules in humans, copper and iron play a crucial role in the respiratory cycle, and cobalt is found in essential biomolecules such as vitamin Bi2-... 

The Transition Metal Sulfides are a group of solids which form the basis for an extremely useful class of industrial hydrotreating and hydroprocessing catalysts. Solid state chemistry plays an important role in understanding and controlling the catalytic properties of these sulfide catalysts. This report discusses the preparation of sulfide catalysts, the role of disorder and anisotropy in governing catalytic properties, and the role of structure in the promotion of molybdenum disulfide by cobalt. 

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