Vanadyl oxalate

Fig. 4. Reduced time plots, fr = (f/fo.s), for the isothermal decomposition of ammonium vanadyl oxalate using master data for the Avrami—Erofe ev equation [eqn. (6), n = 2], by the application of a method of analysis [73] described in the text. The circles are experimental measurements and the lines correspond to exact agreement with the equation. (Reproduced, with permission, from Thermochimica Acta.)...

The catalysts employed in this study consisted of V205/Si02 and Mo03/Si02 prepared by incipient wetness impregnation of the support (Cabosil L90) wiA aqueous solutions of vanadyl oxalate (Aldrich, 99.99%) and ammonium molybdate (Aldrich, 99%), respectively. The catalysts were dried at 623 K for 6 h and calcined at 773 K for 6 h. 

The catalysts were coded VI and V8, and the support (an uncoated pigmentary anatase) ELIO. They were prepared by mixing vanadyl oxalate solution with the support to form a paste that was kneaded before drying and calcination (4h at 723 K) [28b]. Mean... 

Alternate methods The VgOs is fused with an excess of crystalline oxalic acid until a greenish-blue, completely water-soluble mass of vanadyl oxalate is obtained. This mass is then calcined to complete decomposition in the absence of air. The VO3 is obtained as the residue. 

V- Hexagonal MCM- lattice 41 Vanadyl oxalate Sodium silicate HDTMABr Sol-gel method synthesis 120 °C, 96 h Zhang, 2001 (58)... 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

For the synthesis of Mo/V/Te/Nb/O catalysts, ammonium paramolybdate, vanadyl sulfate, ammonium niobium oxalate and tellurium oxide or telluric acid are mixed as aqueous solutions or slurries and dried at about 150°C. These mixed slurries are then calcined at 500-650°C in a N2 stream [39]. In addition to the dominant Ml and M2 phases, impurity phases, for example M0O3, Mo,5V9O40 and Mo3Nb20ii, are also observed [28c]. It should be noted that Mo-V-Te-O catalysts cannot be obtained by the dry-up method. 

A range of vanadyl(IV) complexes have been studied, e.g., VOL + (632) as well as mixed ligand complexes VOLL +, e.g., where L = oxalate (210, 213, 471, 632). VOLX2 (X = Cl, Br) is less tetragonal than V0(H20) from the ligand field point of view (157), i.e., there is less double-bond character in the VO bond when L is present. Quite marked splitting (3700 cm ) of the first excited state ( Eg -> Ai + is found forVCUL (157). 

Vanadium (V, at. mass 50.94) occurs in the V, IV, III, and II oxidation states, vanadium(V) compounds being the most stable. In alkaline medium, the colourless vanadate VOs ions exist, whereas in strongly aeidic media, the yellow V02 cations are present. Within the intermediate pH range polymerized orange-yellow anionic forms occur. Vanadium(V) forms heteropoly acids with P(V), Mo(VI), and W(VI), and also peroxide complexes. Vanadium(IV) occurs as the blue vanadyl ion V02", stable in acid solutions and readily oxidized to vanadium(V) in alkaline solution. The VO cation is amphoteric. At pH 4, V0(0H)2 precipitates and at pH 9 it dissolves. Vanadium(IV) forms fluoride-, oxalate-, and... 

Co-ordination of the GH4 ion is also considered to occur at the lower pH giving V0(0H)2GH4, the high second pK of the gluconic acid making it unlikely that the ligand is the GH dianion. Formation constants have been calculated for the 1 1 1 ternary complexes formed from vanadyl ion oxalic acid and salicylic, sulphosalicylic... 

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