Vanadium appearance

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

We knew the poisonous behavior of nickel, sodium, iron, and copper, and could anticipate the problems connected with them. However, vanadium appeared to offer some new problems. First of all, it appeared in our reduced crudes at one to three times the nickel level. It could be expected to show the same adverse product selectivity as at lower levels, but with much greater severity. 

Nickel.—Vanadium and nickel are miscible in all proportions in the liquid state up to 36 per cent, vanadium. The solid alloys, which contain up to 20 per cent, vanadium, appear to be homogeneous, but those richer in vanadium consist of two kinds of crystals.10 These alloys are made by reducing a mixture of vanadium pentoxide and nickel oxide.u... 

Vanadium appears to mimic the action of insulin. The incubation of rat adipocytes with 10-100 pmol dm-3 V02+ or vanadate stimulates the transport of glucose and 2-deoxyglucose into... 

Surface vanadium appears to be most stable (to reduction) at low (<1%) V concentration when present as monomeric vanadyl units. Its stability decreases with increasing V levels. It is least stable (to reduction) at high (5%) V levels when present as a supported Vanadia phase. This difference in reactivity with V concentrations is believed responsible for the rapid decline in cracking activity observed in dual function cracking catalysts containing alumina when V start to exceed the 1.0-1.25 wt.% level (4). Further details of the mechanism of catalyst deactivation by V age the subject of continuing investigations 1n our laboratories by 31V solid state NMR, XPS, and Raman spectroscopy. 

Although the forward reaction is favored by increase in pressure, this is not employed in practice since 97 to 99% conversion of sulfur dioxide to sulfur trioxide can be accomplished at the temperature specified here, provided suitable catalysts are used. The first catalyst used for this reaction consisted of finely divided platinum dispersed in asbestos, anhydrous magnesium sulfate, or silica gel. Other catalysts were later discovered. Mixtures of ferric and cupric oxides are useful, but these are less efficient than platinum. Certain mixtures containing vanadium pentoxide (V205) and other compounds of vanadium appear to be as good as or better than platinum. There has been much controversy over the relative merits of platinum and vanadium catalysts, and only time will provide the answer as to which is best. 

Compared to a number of other metals, vanadium appears to be relatively innocuous when ingested in low concentrations by animals however, it is by no means certain that this will be true for chronic exposure, as toxic effects have been reported [80], The nutrition community treats vanadium as a member of the ultra trace metals, which have a nutritional requirement of less than 1 mg/kg diet and are present in tissues in the range of micrograms per kg [81]. Although evidence suggests that vanadium is beneficial to human health, its mechanism of action remains obscure. No specific dietary recommendations have been made, in part, because there is controversy surrounding whether or not vanadium is an essential element. 

A hypothesis has been presented, linking accumulation to vanadate reduction81). The influx data support this hypothesis. Selective accumulation of vanadium appears to result from two factors. 

For particulate emissions (particularly in fly ash samples), it has been found that certain elements - antimony, arsenic, lead, cadmium, chromium, cobalt, manganese, nickel, zinc, sulfur, selenium, thallium, and vanadium - appear to be enriched on the surface of the particles in a water-soluble form (Hansen and Fisher 1980 Keyser et al. 

In serum, absorbed vanadium is transported mainly bound to transferrin (Lager-kvist etal. 1986, Kustin and Robinson 1995). Vanadium in rat milk was found mainly in the protein fraction, and perhaps also in lactoferrin (Sabbioni and Rade 1980), in which form it is transferred from the mother to the pups. In older rats, vanadium appears to be converted into vanadyl-transferrin and ferritin complexes in the plasma and body fluids (Edel and Sabbioni 1989, Sabbioni and Marafante 1981). 

Vanadium concentrations in blood, serum or urine are used as a biological indicator of exposure to vanadium. Urine and serum are the specimens with widest application and greatest practicability for monitoring human exposure to vanadium compounds, but urine is preferred as an indicator medium. Blood vanadium appears to be a less sensitive indicator than urinary vanadium, partly because the differences in concentrations are hardly appreciable at low levels of exposure with the analytical methods available (Alessio et al., 1988). 

In Keggin type phosphovanadomolybdate acids (HPAs), vanadium appeared to be the most cracial element for oxidative processes and their strong acidity is known to be favourable to functionalization of alkanes [1]. However, the major drawback of this type of materials is their low surface area (< 10 m /g). In order to overcome this disadvantage, a possible solution is to support them on materials with large surface area. 

Decondensation of the system in this acidity range may be explained by the nature of the coordination sphere of V(V) in the monomer. We noted previously (Section 1.3) that, because of the high polarizing nature of V(V), vanadium appears to be better stabilized in a dioxo-aquo form [V02(OH2)4] involving tt bonds than in oxo-hydroxo-aquo 1 VO(OH)2(OH2)3] or hydroxo-aquo [V(OH)4(OH2)2] forms ... 

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