Cobalt complexes molybdates

Firsova et al. (136) also investigated a cobalt molybdate catalyst containing a small amount of Fe3+, after exposure to a reaction mixture of propylene and oxygen. The authors observed the valence change of Fe3+ to Fe2+ and the formation of a surface complex between the hydrocarbon and the iron (Fe—O—C—). In contrast to pure iron molybdate which also forms a surface Fe—O—C— complexes, the electronic transitions in the cobalt iron molybdate were reversible. The observed valence change showed that iron ions increase the electronic interaction between ions in the catalyst and the components of the reaction mixture. 

Cobalt and rhodium yield complex molybdates which are chemically" and crystallographically analogous to the corresponding complex molybdates of aluminium, iron, and chromium.1... 

Numerous complex molybdates of cobalt have been prepared and described.8... 

Hydrogen sulphide reacts reversibly with many unsaturated or aromatic hydrocarbons, in the presence of mixed oxide catalysts, to produce thiophens these may be polycyclic, according to the complexity of the starting hydrocarbon. This reaction, which is believed to be the source of many of the sulphur compounds found in crude oil, has been studied in particular by Klemm and his co-workers, who have now published their detailed results. A typical example is the formation of the isomeric benzonaphthothiophens (15) and (16) from the reaction of 2-phenylnaphthalene (14) with hydrogen sulphide over a sulphided cobaltous oxide-molybdic oxide-alumina catalyst at 450—630 in a flow system. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Hydrotreating catalysts are composed of cobalt or nickel molybdate or nickel tungstate on an alumina or zeolite support. The materials are sulfided with hydrogen sulfide (H2S) before use, but the final catalysts may retain some oxide and be of complex composition. 

Molybdenum oxide - alumina systems have been studied in detail (4-8). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support (9-11). Richardson (12) studied the structural form of cobalt in several oxidic cobalt-molybdenum-alumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit (10) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% M0O3 and 4 wt% CoO. They concluded that a cobalt aluminate phase was present and could not find indications for an active cobalt molybdate complex. Recent magnetic susceptibility studies of the same type of catalyst (13) confirmed the conclusion of Lipsch and Schuit. 

The tetrasulfo-Pc complexes of a number of metals are made by the urea melt process by heating the powdered metal, or its acetate, with triammonium-4-sulfophthalate, urea, boric acid, and ammonium molybdate. The metals or metal compounds used are those of chromium (III), manganese(II), iron(II), iron(III), cobalt(II), and zinc(II). Selected synthetic examples of sulfo- and other derivatives of metal phthalocyanines are presented below. 

The original catalysts reported for the metathesis of acyclic alkenes were related to alkene polymerization systems. Banks and Bailey reported in 1964 that the heterogeneous cobalt molybdate complexes would promote the metathesis reaction. Since that time a wide variety of catalysts that use Mo, W and Re as Ae active metal in combination with a variety of supports, promoters and activation conditions have been reported. These heterogeneous catalysts are the systems of choice for most industrial fine chemical applications. 

Gomez et al. " electrodeposited Co-Mo magnetic alloys from a sulfate-citrate bath on carbon electrodes. Although the focus of their paper was not on elucidating the mechanism of induced codeposition, it was suggested that hydrogen could not be responsible for the deposition of Mo in the Co-Mo system, because its concentration was fairly low and because another mechanism should explain the need for citrate or polycarboxylate anions in solution. The deposition process was foimd to be favored when molybdate was present in solution, even at very low concentrations. Hence, the authors adopted the model of Podlaha and Landolt, according to which a mixed-metal complex of cobalt(II), citrate and molybdenum dioxide is adsorbed on the surface and promotes Mo reduction. 

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