Vanadium catalysts halogenation

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

In addition to titanium-based Ziegler-Natta catalysts, vanadium-based systems have also been developed for PE and ethylene-based co-polymers, particularly ethylene-propylene-diene rubbers (EPDM). Homogeneous (soluble) vanadium catalysts produce relatively narrow molecular mass distribution PE, whereas supported V catalysts give broad molecular mass distribution.422 Polymerization activity is strongly enhanced by the use of a halogenated hydrocarbon as promoter in combination with a vanadium catalyst and aluminum alkyl co-catalyst.422,423... 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

Valence, 286 Valence electrons, 269 and ionization energies, 269 Vanadium atomic radius, 399 eleciron configuration, 389 oxidation numbers, 391 pentoxide catalyst, 227 properties, 400, 401 van der Waals forces, 301 elements that form molecular crystals using, 301 and molecular shape, 307 and molecular size, 307 and molecular substances, 306 and number of electrons, 306 van der Waals radius, 354 halogens, 354 Vanillin, 345... 

Most other peroxidases are Fe-heme-containing systems, which function as two-electron redox catalysts (Scheme 8). Dihydrogen peroxide oxidizes the Fe-heme moiety by two electrons, forming Compound 1 (a heme + FeIV=0 species) [97], Compound 1 oxidizes the halide ion, forming the active halogenating species. This mechanism cannot be operative in V-BrPO because the vanadium is already in its highest accessible oxidation state. Moreover, native V-BrPO does not oxidize bromide without an acceptable peroxide source. However, it should... 

Interest in the industrial production of nitriles has increased, and vanadium phosphate catalysts have shown great promise, giving high selectivities and yields in the conversion of halogenated methyl... 

Catalysts for the oxidation of volatile organic compounds (VOC) are generally supported platinum or palladium catalysts. Copper oxide, vanadium oxide and chromium oxide are suitable for the oxidation of halogenated compounds. 

In order to overcome certain difficulties such as the dissipation of heat and the use of inflammable mixtures, certain liquid phase processes have been proposed for the oxidation of aromatic hydrocarbons and compounds. In such a process 100 the aromatic hydrocarbons or their halogenated derivatives are treated with air or gas containing free molecular oxygen in the liquid phase at temperatures above ISO0 C. and under pressure in the presence of a substantial quantity of liquid water. A small quantity of such oxidation catalysts as oxides or hydroxides of copper, nickel, cobalt, iron or oxides of manganese, cerium, osmium, uranium, vanadium, chromium and zinc is used. The formation of benzaldehyde from toluene is claimed for the process. 

Halogen substituted toluenes are readily converted into nitriles because electron-withdrawing substituents enhance the reactivity of such compounds in the ammoxidation reaction. The fluoro-, chloro-, bromo-, and iodo-substituted toluenes [e. g. 41,74-76] can, therefore, be converted to the corresponding nitriles. Whereas the conversion rate of /7-halotoluenes (over vanadium phosphate catalysts [41,75]) is nearly independent of the nature of the halogen substituent, the selectivity decreases in the sequence p-Cl > /7-Br >> p-l. Ammoxidation of isomeric chloro-toluenes results in different conversion p o > m) and selectivity p > o > m) sequences [41,75,76]. 

Although presently lacking industrial importance, alternating copolymers can be made from propylene and butadiene, also from propylene and isoprene. Copolymers of propylene and butadiene form with vanadium- or titanium-based catalysts combined with aluminum. alkyls. The catalysts have to be prepared at very low temperature (-70 C). Also, it was found that a presence of halogen atoms in the catalyst is essential.Carbonyl compounds, such as ketones, esters, and others, are very effective additives. A reaction mechanism based on alternating coordination of propylene and butadiene with the transition metal was proposed by Furukawa. ... 

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