Vanadium-chromium oxide compounds

Mixed vanadium-chromium oxide compounds present a wide range of interesting properties for instance, they have excellent catalytic properties, and recently they were shown to be potential candidates for anodes in lithium-ion batteries. DTA, TG and powder XRD analyses were used [101] to monitor the dehydration/crystallization and phase transitions upon heat treatment of the hydrated vanadates obtained through the reaction of peroxo-polyacids of vanadium and chromium, and to determine the ranges of coexistence of the phases in equilibrium. 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Titanium, vanadium or chromium oxides activated with chlorine-free organo-aluminum compounds, triethyl- or triisobutyl aluminum, have also been used as catalysts [285],... 

The halide is not the only metal compound used as source of metal. Metal oxides and sulfides are employed to prepare vanadium, chromium, iron and nickel borides in this way from sulfides at lower reaction T than those required by reaction sintering of the elements . 

A. Oxidation with Vanadium, Chromium and Molybdenum Compounds. .. 1273... 

Soudan, P., Pereira-Ramos, J.P, Farcy, J., Gregoire, G., and Baffler, N. 2000. Sol-gel chromium-vanadium mixed oxides as lithium insertion compounds. Solid State Ionics 135, 291-295. 

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. 

Acrolein conversion takes place in the presence of catalysts based on mixed oxides of molybdenum and vanadium, doped by compounds of tungsten, copper, chromium, tellurium. arsenic, etc., and designed te improve low-temperature activity, productivity, and mechanical performance. They operate aroud 250 to 280 0, at between 0.L and 0.2.10 Pa absolute, also in the presence of steam (water to acrolein molar ratio about... 

Iodine forms compounds with all elements except the noble gases, sulfur, and selenium, but only reacts indirectly with carbon, nitrogen, oxygen, and some noble metals. Ferric and cupric salts, and compounds of vanadium, chromium, and manganese in their highest oxidation status are reduced in acid solution by iodide ions, with liberation of free iodine. Iodine reacts with hydrocarbons, but equilibria are often unfavorable because hydrogen iodine is liberated, which may reduce the alkyl iodide to the hydrocarbon with formation of iodine. 

Monomeric species M OR-tert)x have been characterized for titanium, vanadium, chromium, zirconium, and hafnium (x = 4) and for niobium and tantalum (x == 5). With chromium it was found that limiting Cr(III) to coordination number 4 in the dimeric Cr2(OBu )e caused instability and a remarkable facility toward valency disproportionation or oxidation to the stable quadricovalent Cr(OBu )4 (8, 9). In contrast, molybdenum formed a stable dimeric tri-tert-butoxide (Bu O)3Mo=Mo-(OBu )3 which is diamagnetic and presumably bound by a metal-metal triple bond (10, II). Yet another interesting feature of chromium is the synthesis of a stable diamagnetic nitrosyl Cr(NO) (OBu )3 in which the nitric oxide is believed to act as a three-electron donor with formation of a four-coordinated low spin chromium (II) compound (12). The insta-bihty of Cr2(OBu )e and the stability of both Cr(NO) (OBu )3 and Cr(OBu )4 must result from the steric effects of the tertiary butoxo groups since the less bulky normal alkoxo groups form very stable polymeric [Cr(OR)3]a. compounds in which the Cr(III) has its usual coordination number of 6 (octahedral). 

Zeotype materials containing metal cations, for example ions of titanium, vanadium, chromium, iron, or tin, in the tetrahedral positions of their frameworks have been explored as solid Lewis acid catalysts (Ig). Such materials have been shown to be active in the Meerwein—Pormdorfr-Verley reduction of carbonyl compounds (151,233), and the BV oxidation (also called BV rearrangement) (234). 

Various other solvate complexes can be obtained, when transition, metals are reacted with the free halogens in acetonitrile . In this way TiCl4(AN)2, TiBr4(AN)2 and a polyhalide [Ti(AN)6] [Isis are produced. Chlorine, bromine and iodine oxidize vanadium to trivalent compounds, namely VCl3(AN)3AN, [VBr2(AN)4]Br and the polyiodide [V(AN)6][Is]s- With chromium CrCls(AN)3AN, a bromide of variable (composition and [Crl2(AN)4]I are obtaincd. ... 

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