Metavanadate anion

The polymeric metavanadate anions have been described above. Upon warming or ageing solutions that contain the decavanadate ion, it is possible to precipitate salts of the dark red trivanadate anion, MV3Os (M = NH4, K, Rb, Cs). The formula is sometimes written as M2V60i6, and the salts called hexavanadates in the literature. Potassium and cesium trivanadate contain infinite buckled layers of distorted VOs and VOe polyhedra.18 Another layer structure is found in yellow K3VsOi4 which also is deposited from aqueous solution. The [V5O14]3 - anion is composed of layers of comer-shared V04 tetrahedra and VO5 square pyramids.19... 

A titania (TiOa) sample with a large surface area (300 m g ) was chemically modified with 3-aminopropyltrimethoxysilane (APS) under a reflux of toluene. The thermal stability of the modified TiOa (APS-Ti02) and the adsorptivity of metavanadate anion (VO3 ) on APS-TiOz from an aqueous solution were investigated. Modification with APS suppressed crystal growth and transformation of anatase crystallite to rutile upon calcination, and the anatase phase was preserved even after calcination at 1000°C, while transformation to rutile in the unmodified TiOz samples was observed at around 800°C. Since there was little crystal growth in APS-TiOz, it possessed a large surface area of 205 m g after calcination at 700°C. The amount of adsorbed on APS-TiOz was ca. 

We applied this technique to the preparation of VaOs/TiOz catalysts and here report the effect of organosilane on the thermal stability of a TiOa support with a large surface area, the adsorption properties of metavanadate anion (VO3 ), and the SCR activities of supported V2O5 catalysts prepared from VOj -adsorbing TiOa supports. 

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

The vanadate(V) anions give rise to numerous salts. Among the most common are the orthovanadates (V04 ), metavanadates and... 

Salts with Condensed Octahedral-Like Oxo-Anions Chains of oxo-anions can condense giving rise to octahedral-like chains or mulhple chains. This is the case, for example, for several metavanadates forming double chains [(V20,5) "] such as... 

In the solid state, metavanadates M[V03] exist. These are hydrolysed to orthovanadate [Equation (2.6a)], and further condense to oligovanadates when dissolved in water [Equation (2.6b)]. The term solutions of metavanadate often encountered in the literature, particularly in biochemical and pharmaceutical contexts, refers to such a mixture, mainly containing [H2V04], [H2V207] and [V40i2] . The orthovanadate anion liberated as orthovanadates M3[V04] are dissolved in water reacts as a Brpnsted base [Equation (2.6c)] orthovanadate solutions thus are alkaline. Meta- and orthovanadates also occur naturally in the form of minerals, along with di-, hexa- and even decavanadates cf. Table 1.1. 

The reference applied in quoting chemical shifts is neat VOCI3, for which the chemical shift 8 is set to zero. Since VOCI3 is rather an aggressive liquid, which is readily hydrolysed in moist air, the use of a more easily manageable, auxiliary standard may be useful. An aqueous solution of 1 m sodium metavanadate at pH 12 is sometimes employed, which contains the anions 04 (6 = -535.7ppm) and 207 (8 = -559.0ppm). V NMR spectroscopy has recently been reviewed.[ 1... 

This equilibrium is described by the constant of 3.1 X 1015 for the case of phosphates, and 4.7 X 1013 for acidic arsenates. For metavanadate solutions an estimation of the value of the similar constant failed owing to the levelling of the acidic properties of this Lux acid. The next stage of the titration is the formation of neutral salts as a result of acid-base neutralization of the formed pyro-anions, this stage is described by the following equation ... 

Crystal structures of sodium or ammonium metavanadate are composed of chain linkages of VO4 tetrahedra, 6 (20,21), similar to those of metaphosphates with high molecular weights. Anionic structures of... 

Preliminary studies have shovTi that reducing sugars and their reduction products migrate, during electrophoresis in sodium metavanadate solution, as anionic complexes. However, this electrolyte has not been examined further. 

Amino nitroxides, 383 5-Aminotetrazoles, 336, 337 N-Amino-2,4,6-triphenylpyridinium perchlorate, 409 Ammonium acetate, 11 Ammonium cerium(IV) sulfate, 56 Ammonium metavanadate, 418 5a-Androstane-3(3.17 3-diol, 6 5a-Androstane-3d-ol-17-one, 6 A -Androstene-3,17-dione, 167 Angustmycin, 407 2,S -Anhydronucleosides, 88 Anhydrovinblastine, 389 Anion exchange resins, 69 Annelation, 71, 90, 148 Anthraquinone, 29 Anthrasteroids, 167 Antimony(V) chloride, 12 Apomorphine, 236... 

Acidified vanadate(V) yields a brown precipitate with alkahs, soluble in excess. Excellent solvents for V2O5 are either OH" or C03 ", with a small (catalytic) amoimt of peroxide, forming ions having formulas like those of the mono-and linear polyphosphates as [V 03 +i] " ", depending on conditions. Cyclic [( 03)4] " and [(V03)s] " are especially prominent at 6.5 [Pg.102]

In the solid, metavanadates have linear anionic structures [46,55] infinite chains of corner-sharing (KVO3) letrahedra, or distorted trigonal bipyramids (KV03-H20), in which vanadium is pentacoordinaled (Figure 4.13). 

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