Molybdenum promoted vanadium

On metals that produce substantial yields of oxygenates, such as rhodium, promotion by reducible oxides (e.g., molybdenum or vanadium oxides) appears beneficial 76—78). The key property of the cation of the promoting oxide is a weak affinity for CO combined with a strong affinity for oxygen. An aftractive hypothesis to explain the role of the promoting cations is that the reducible cation provides a site for the O atom generated upon CO dissociation, whereas CO interacts only weakly with the promoting cations. 

Bej and Rao (186-190) conducted a detailed investigation of molybdenum- and cerium-promoted vanadium phosphate catalysts. They foimd an increase in the selectivities of these catalysts as a result of incorporation of the promoters, albeit with slight decreases in activity. They attributed the improved selectivity to a role of the promoters in preventing overoxidation of the MA to carbon oxides. They also found that the promoted catalysts could withstand more severe reaction conditions than the unpromoted catalyst, and this property was also attributed to the formation of less carbon oxides, which can poison the catalyst. 

Bej and Rao [166-170] conducted a detailed study of molybdenum- and cerium-promoted vanadium phosphate catalysts. They found an increase in the selechvity... 

Molybdenum and vanadium promote nitrogen fixation by A. chroococcum,A. vinelandii and Bac. amylobacter, [in the case of] molybdenum up to the 100-fold of the amount accomplished in the absence of theses elements hy Azotobacter. From this it is concluded that without molybdenum or vanadium there is no possibility for any appreciable nitrogen fixation. ... 

Electrolytes used are sulfuric acid, hydrochloric acid, sodium hydroxide, inorganic salts, and organic salts. Glacial acetic acid, methyl alcohol, and ethyl alcohol have also been found useful. Promoters are stannous chloride, copper sulfate, mercurous sulfate, antimony oxides, ketones, and salts of lead, titanium, molybdenum, and vanadium. 

The additive elements used to enhance the performance of the Fe-Sb-0 catalyst either enter the iron antimonate rutile phase to form a solid solution (49,50) or they form separate rutile phases (44). The promoter elements that produce the best performing iron antimonate-based ammoxidation catalysts are copper, molybdenum, tungsten, vanadium, and tellurium. Copper serves as a structural stabilizer for the antimonate phase by forming a rutile-related solid solution (23). Molybdenum, tungsten, and vanadium promote the redox properties of iron antimonate catalysts (51). They provide redox stability and prevent reductive deactivation of the catalyst, especially under conditions of low oxygen partial pressure (see above). The tellurium additive produces a marked enhancement of the selectivity of iron antimonate catalyst. How the tellurium additive functions to increase selectivity is not clear, but the presumption is that it must directly modify the active site. In fact, it is likely that it can actually serve as the site of selective oxidation because in its two prevalent oxidation states Te + and Te +, tellurium possesses the requirements for the selective (amm)oxidation site, a-hydrogen abstraction, and 0/N insertion (see below). 

The essential microelements are only required in trace amounts (see also p.2). This group includes iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), cobalt (Co), chromium (Cr), selenium (Se), and molybdenum (Mo). Fluorine (F) is not essential for life, but does promote healthy bones and teeth. It is still a matter of controversy whether vanadium, nickel, tin, boron, and silicon also belong to the essential trace elements. 

We studied the oxidation of cyclohexene at 70°C in the presence of cyclopentadienylcarbonyl complexes of several transition metals. As with the acetylacetonates, the metal center was the determining factor in the product distribution. The decomposition of cyclohexenyl hydroperoxide by the metal complexes in cyclohexene gave insight into the nature of the reaction. With iron and molybdenum complexes the product profile from hydroperoxide decomposition paralleled that observed in olefin oxidation. When vanadium complexes were used, this was not the case. Variance in product distribution between the cyclopentadienylcarbonyl metal-promoted oxidations as a function of the metal center were more pronounced than with the acetylacetonates. Results are summarized in Table V. 

The only system which seems to be promising for industrial application is ruthenium promoted with rubidium on graphite as carrier (see Section 3.6.2.3). Further information on structure, activity and reaction mechanism of non-iron catalysts is given in [102], [172]-[175], Specific references vanadium [176], uranium [177], molybdenum [178]-[180], tungsten [181]. 

Much more interesting, however, is the observation by Simpson [36] that molybdenum is always observed on the surface of used catalysts, despite the presence of up to 85 wt% V and 20 wt% Ni on the catalyst. Evidently molybdenum sulphide can migrate readily through the deposit to the surface, a finding confirmed by at least two other studies [40, 41]. As a result, there may well be combinations of sulphided nickel, vanadium and molybdenum at the surface of the catalyst and available to promote further hydroprocessing. 

Ethylbenzene dehydrogenation is generally catalyzed by a potassium-promoted iron oxide catalyst. The most widely used catalysts are composed of iron oxide, potassium carbonate, and various metal oxide promoters. Examples of metal oxide promoters include chromium oxide, cerium oxide, molybdenum oxide, and vanadium oxide. " The potassium component substantially increases catalyst activity relative to an unpromoted iron oxide catalyst. Potassium has been shown to provide other benefits. In particular, it reduces the formation of carbonaceous deposits on the catalyst surface, which prolongs catalyst life. 

The most studied systems for oxidative propane upgrading are vanadium [2], vanadium-antimony [3], vanadium-molybdenum [4], and vanadium-phosphorus [5] based catalysts. Another family of light paraffin oxidation catalysts are molybdenum based systems, e.g. nickel-molybdates [6], cobalt-molybdates [7] and various metal-molybdates [8-9]. Recently, we investigated binary molybdates of the formula AM0O4 where A = Ni, Co, Mg, Mn, and/or Zn and some ternary Ni-Co-molybdates promoted with P, Bi, Fe, Cr, V, Ce, K or Cs [10-11]. A good representative of these systems is the composition Nio.5Coo.5Mo04 which was recently selected for an in depth kinetic study [12] and whose mechanistic aspects are now further illuminated here. 

There seems to be no literature about the direct oxidation of ethane to acetic acid over heteropolycompounds catalysts. Nevertheless, there is a limited amount of literature[10,26-28] about direct oxidation of ethane to acetic acid over oxide catalysts at low temperature (200-350 C). It seems that vanadium and molybdenum are necessary to those catalysts, and the addition of water is useful to increase the production of acetic acid. Roy et al. [10] has proved that vanadium and molybdenum phosphates supported on Ti02-anatase were effective in the direct oxidation of ethane to acetic acid. Considering previous research results, it is suggested that other promoters, such as trcmsition-metal oxides, are necessary to enhance the catalytic activity of the activated H3PMol2O40(Py) in the direct oxidation of ethane to acetic acid. 

Stress-relief cracking has been found in vessels fabricated from boron-treated carbon-molybdenum steel and in vanadium-treated steels of the type shown in Table 4-16. Laboratory tests have confirmed that molybdenum, vanadium and boron promote stress-relief cracking, and that boron and vanadium have a stronger effect than molybdenum. In marginal applications, a 2-1/4-Cr 1-Mo steel would be expected to behave better than boron-treated or vanadium steels, and practical experience seems to bear this out. 

Antimonate-Based Catalysts. In addition to the bismuth-molybdenum oxide catalyst system, several other mixed metal oxides have been identified as effective catalysts for propylene ammoxidation to acrylonitrile. Several were used commercially at various times. In particular, the iron-antimony oxide catalyst is currently used commercially by Nitto Chemical (now Dia-Nitrix Co. Ltd., Japan) and its licensees around the world, although the catalyst was originally discovered and patented by SOHIO (20,21) and by UCB (22). Nitto Chemical improved the basic iron-antimony oxide catalyst with the addition of several elements that promote activity and selectivity to acrylonitrile. Key among these additives are tellurium, copper, molybdenum, vanadium, and tvmgsten (23-25). 

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