Mo oxide systems

Annenkova et al. (105) studied both the physicochemical and catalytic properties of the Bi-Fe-Mo oxide system. The X-ray diffraction, infrared spectroscopic, and thermographic measurements indicated that the catalysts were heterogeneous mixtures consisting principally of ferric molybdate, a-bismuth molybdate, and minor amounts of bismuth ferrite and molybdenum trioxide. The Bi-Fe-Mo oxide catalysts were more active in the oxidation of butene to butadiene and carbon dioxide than the bismuth molybdate catalysts. The addition of ferric oxide to bismuth molybdate was also found to increase the electrical conductivity of the catalyst. 

Sleight and Jeitschko (107) studied the Bi-Fe-Mo oxide system by X-ray diffraction. They reported the formation of a ternary compound, Bis(Fe04) (Mo04)2. The X-ray pattern of this compound was similar to that reported for compound X by Batist (106). 

LoJacono et al. (108) also utilized X-ray diffraction methods to study the structural and phase transformations which occurred in the Bi-Fe-Mo oxide system. They detected two ternary compounds containing bismuth, molybdenum, and iron. One of the compounds formed when the atomic ratio Bi/Fe/Mo = 1 1 1 the other formed when the atomic ratio Bi/Fe/Mo = 3 1 2. The X-ray data indicated a close structural relationship of the bismuth iron molybdate compounds with the scheelite structure of a-phase bismuth molybdate. Moreover, their structures were similar to compound X. The structure of the Bi/Fe/Mo = 3 1 2 compound was identical to the compound reported by Sleight and Jeitschko (107). The authors proposed that the structures of both of the compounds could be viewed as resulting from the substitution of Fe3+ in the a-phase lattice. In the Bi/Fe/Mo = 1 1 1 compound, 1 Mo6+ ion is replaced by 2 Fe3+ ions one Fe3+ ion occupies a Mo6+ site the other Fe3+ ion occupies one of the vacant bismuth sites. In the Bi/Fe/Mo = 3 1 2 compound, the Fe3+ ion replaces one Mo6+ ion while the additional Bi3+ ion occupies one of the vacant bismuth sites. 

The creation of selective catalysts for such complex reactions seems to be an especially difficult problem. Nevertheless, surprisingly, selective catalysts have been developed for complex reactions, which can be exemplified by the oxidation and ammoxidation of propylene, oxidation of butene and even butane to maleic anhydride (which requires seven oxygen atoms). Such reactions are usually performed over V and Mo oxide systems [4, 6, 8-10]. High selectivity of these systems is presumably provided by a special structure of the catalyst surface that allows control... 

The selective oxidation of toluene has been studied over a number of catalysts based on metal oxides, with the U/Mo oxide system being one of the most achve and selective[50, 51]. The main products in the oxidation of toluene, excluding the non-oxidative coupling products, were benzaldehyde, benzoic acid, maleic anhydride, benzene, benzoquinone, CO and CO2. Under the same reachon condihons toluene may also yield coupling products such as phthalic anhydride, methyldi-phenylmethane, benzophenone, diphenylethanone and anthraquinone, as shown by Zhu and coworkers [51]. A range of different uranium-based oxides were tested [51] and the results obtained are shown in Table 13.4. 

There have been few studies on mixed compounds of iron, chromium and aluminum molybdates. Abidova and co-workers(7 -79) made a somewhat inconclusive study on the mixed Fe/Al/Mo oxide system. Based on DSC and reflectance measurements on the ... 

In this work, pure or silica-dispersed Nb-V systems were prepared by either the hydrolytic or the non-hydrolytic procedures. Moreover, the hydrolytic sol-gel route was extended to the preparation of pure or silica-dispersed Sb-V and Nb-V-M (M = Sb, Mo) oxide systems. The catalytic performances of these mked-oxide systems in propane oxidative dehydrogenation were investigated. 

Structural studies of the vanadium-molybdenum catalysts so widely used in oxidation to acids were made by Munch and Pierron 163). Compounds identified were MogVg04o and M04V5O25. These compounds were observed in catalysts used for the oxidation of benzene to maleic anhydride. The pure crystalline compounds were not as active as commercial catalysts, however. Another study of the V-Mo oxide system was made by Pop 164). 

Supported bimetallic systems containing molybdenum and a modifier such as Co, Ni... are frequently encountered in the literature, especially as desulfurisation catalysts. On the other hand, little attention has been devoted to Pd-Mo/oxide systems so far, despite their use for the CO + NO reaction by Halasz et al. [1] and several mentions as selective hydrogenation catalysts in the patent literature. 

Monooxygenases (MOs) Enzyme systems of the endoplasmic reticulum of many cell types, which can catalyze the oxidation of a great diversity of lipophilic xenobiotics, are particularly well developed in hepatocytes. Forms of cytochrome P450 constitute the catalytic centers of monooxygenases. 

Urea complex with hydrogen peroxide (UHP) seems to be a very useful and convenient oxidation system in nonaqueous medium. The UHP reaction proceeds in methanol and is catalyzed by Mo (VI), W (VI) salts, or SeC>2 (83). Catalytic oxidation in a water-free medium can be carried out with alkylhydroxyperoxides, the catalysts being titanium alkoxides (84) or selenium compounds (85). The reaction appears to proceed quickly and with good selectivity. 

Long-chain derivatives of pyrazolyl pyridines coordinated to MoO(02)2 as 35 may efficiently replace the conventional Mo(CO)e in the oxidation of several double-bond typologies with TBHP, in non-polar hydrocarbon solvents . The epoxidation of cyclopentene and 2,3-dimethyl-2-butene led to the corresponding epoxides, notoriously sensitive to ring opening, in 100% and 87% yield respectively, in isoctane, with 1 hour reaction time. Recent advances in the epoxidation of a-pinene and other terpenes using the Mo-TBHP system have been reported. ... 

Alkyl hydroperoxides in association with V- and Mo-based catalysts were reported to efficiently convert tertiary amines to N-oxides . Lower or trace product yields are observed in the oxidation of secondary amines employing similar oxidizing systems . 

For specific cases such as olefin oxidation over Bi-Mo oxide combinations some information concerning the oxidation mechanism is available. The work of Adams and Jennings (2), of Sachtler (16), and of Adams (1) has led to the general acceptance of an allylic intermediate. The discoverers of the Bi-Mo catalyst system (21) showed that propene is converted to acrolein, while Hearne and Furman (9) proved that butene forms butadiene. The allylic intermediate therefore can in principle react in two different ways (1) formation of a conjugated diene... 

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