Vanadium Estimation

Oxidation of methanol to formaldehyde with vanadium pentoxide catalyst was first patented in 1921 (90), followed in 1933 by a patent for an iron oxide—molybdenum oxide catalyst (91), which is stiU the choice in the 1990s. Catalysts are improved by modification with small amounts of other metal oxides (92), support on inert carriers (93), and methods of preparation (94,95) and activation (96). In 1952, the first commercial plant using an iron—molybdenum oxide catalyst was put into operation (97). It is estimated that 70% of the new formaldehyde installed capacity is the metal oxide process (98). 

Vanadium. Vanadium is essential in rats and chicks (85,156). Estimated human intake is less than 4 mg/d. In animals, deficiency results in impaired growth, reproduction, and Hpid metaboHsm (157), and altered thyroid peroxidase activities (112). The levels of coen2yme A and coen2yme Q q in rats are reduced and monoamine oxidase activity is increased when rats are given excess vanadium (157). Vanadium may play a role in the regulation of (NaK)—ATPase, phosphoryl transferases, adenylate cyclase, and protein kinases (112). 

In many of the transition metals, such as titanium, vanadium and molybdenum, carbon, nitrogen and oxygen atoms can fit into octahedral holes, and hydrogen into the teualredral holes. The fit here is estimated by assuming the atoms all have incompressible radii, and die contact must be such tlrat tire interstitial atoms do not rattle around in the holes. 

Similar calculations were carried out for the single impurity systems, niobium in Cu, vanadium in Cu, cobalt in Cu, titanium in Cu and nickel in Cu. In each of these systems the scattering parameters for the impurity atom (Nb, V, Co, Ti or Ni) were obtained from a self consistent calculation of pure Nb, pure V, pure Co, pure Ti or pure Ni respectively, each one of the impurities assumed on an fee lattice with the pure Cu lattice constant. The intersection between the calculated variation of Q(A) versus A (for each impurity system) with the one describing the charge Qi versus the shift SVi according to eqn.(l) estimates the charge flow from or towards the impurity cell.The results are presented in Table 2 and are compared with those from Ref.lc. A similar approach was also found succesful for the case of a substitutional Cu impurity in a Ni host as shown in Table 2. 

The process of oxygen removal from the metal-oxygen solid solution via the formation of carbon monoxide is known as carbon deoxidation. The terms [0]M and [C]M denote the oxygen and the carbon dissolved in the metal to be refined, for example, vanadium. The extent to which carbon deoxidation can occur in a metal under given conditions of temperature and pressure can be estimated by using the following relationship ... 

It has been suggested that an increase in the coordination number of vanadium from 4 to 5 already takes place in the second protonation step, i.e. when [H2V04] is formed (21). For reactions (1) and (2), however, the protonation constants and thermodynamic parameters are comparable with those reported for P04 and As04 , providing firm evidence that reaction (2) is not accompanied by incorporation of water in the vanadate ion (15, 17). Further, the estimated thermodynamic quantities for reaction (6), AH° = -39 kJ/mol and AS0 = —51 J/(mol K), obtained by extrapolation from the experimental values for reactions (1) and (2) and those for the three protonation steps of P04 and As04 , are not typical of a simple protonation reaction (17). For such a reaction the entropy change is normally a positive quantity often amounting to 100 50 J/(mol K) and the enthalpy... 

The structures of the anhydrous vanadiumfiii) sulphates, 2(804)3, yellow (monoclinic) and green (rhombohedral), have been investigated, and a new double sulphate, (NH4)3V(S04)3, has been prepared and extensively characterized. Single-crystal magnetic susceptibility studies (1.5—20 K) of guanidi-nium vanadium(iii) sulphate have been reported, and the zero-field splitting has been estimated as 3.74 cm . ... 

The equilibrium constant for the formation of [V02(H2edta)] has been estimated as 1.66 x 10. Vanadium)v)-hydroxycarboxylato- and -polyalcohol complexes have been observed in acidic media, and were shown to be primarily tetravanadato-complexes which are broken down by an excess of... 

As a general rule, it can be stated that all elements with electronegativity in the range 1.35-1.82 do not form stable hydrides [34]. Exemptions are vanadium (1.45) and chromium (1.56), which form hydrides, andmolybdenum (1.30) and technetium (1.36), where hydride formation would be expected. The adsorption enthalpy can be estimated from the local environment of the hydrogen atom on the interstitial site. 

A feasibility study on the application of H-NMR petroleum product characterization to predict physicochemical properties of feeds and catalyst-feed interactions has been performed. The technique satisfactorily estimates many feed properties as well as catalyst-feed interactions to forecast products yield. There are, however, limitations that have to be understood when using the H-NMR method. The technique, in general, is not capable either to estimate the level of certain contaminants such as nitrogen, sulfur, nickel, and vanadium when evaluating feed properties or the effect of these contaminants on products yields while testing catalyst-feed interactions. 

Average size measured by SEM, t>Estimated from surface area, Measured by BET method, Atomic ratio of Si to Vg rf, where Vg rf is the amount of surface vanadium atoms. 

In the first stage of the investigation the catalyst can be considered in the form of powder in order to derive intrinsic transient kinetics of all the relevant reactive processes. To this purpose, dynamic reactive experiments can be performed in a simple tubular fixed-bed microreactor over small quantities (50-200 mg) of finely powdered catalyst in principle, this guarantees negligible transport limitations and more controlled conditions (e.g. isothermal catalyst bed), hence enabling a direct estimation of intrinsic rate parameters by kinetic fit. Internal diffusion limitations are particularly relevant to the case of bulk (extruded) monolith catalysts, such as vanadium-based systems for NH3/urea SCR however, they... 

A similar preparative procedure was used to isolate tetrahedral complexes of bidentate donors (L = bipy or phen) [VL2](SCN)3. However, complexes of vanadium(lll) chloride or bromide with these same bidentate donors have stoichiometries depending on conditions.199 With excess of bipy or phen, complexes [VX JX were obtained. In EtOH or in MeCN two series of complexes were isolated. VC13LL (L = bipy or phen L = EtOH or MeCN) and [VC12L2]+ + [VCUL]-. In the reaction of vanadium(III) with phenanthroline202 203 or bipyridine204 there is evidence for extensive hydrolysis. Spectrophotometry was used to estimate the equilibrium constant (Kcq = 0.43) for the reaction in equation (7). 03... 

For the vanadophore region, the sulfate concentration has been estimated to be of the order of 1.3 M and pH 2.349 With no evidence for a stable complex within the vanadocyte, Figure 14 depicts an interesting mechanism proposed for vanadium and sulfate accumulation.350 Anionic vanadium(V) (as HVO ") and sulfate ions enter the cell. Provided that within the vanadophore there is a strong reducing agent, vanadium can be reduced to vanadium(IV) and vanadium(III), cationic at the low pH in the vanadophore. If the vanadophore membrane is permeable to anions but not cations, the reduced vanadium remains trapped. 

Vanadium predpitates the metal from solutions of salts of gold, silver, platinum, and iridium, and reduces solutions of mercuric chloride, cupric chloride and ferric chloride to mercurous chloride, cuprous chloride, and ferrous chloride, respectively. In these reactions the vanadium passes into solution as the tetravalent ion. No precipitation or reduction ensues, however, when vanadium is added to solutions of divalent salts of zinc, cadmium, nickel, and lead. From these reactions it has been estimated that the electrolytic potential of the change, vanadium (metal)—>-tetravalent ions, is about —0 3 to —0 4 volt, which is approximately equal to the electrolytic solution pressure of copper. This figure is a little uncertain through the difficulty of securing pure vanadium.5... 

Lead Metavanadate, Pb(VOg)2.—Acid solutions of vanadates on being treated with lead salts give rise to yellow basic vanadates the composition of which varies with the conditions. The precipitation of normal lead vanadate is, therefore, difficult. It has been accomplished by the addition of lead acetate to ammonium metavanadate solution in the presence of acetic acid.2 The lead precipitates contain all the vanadic acid originally present in solution, and precipitation of vanadates with lead salts has, therefore, been employed for the quantitative estimation of vanadium.3 The mineral deschenite consists chiefly of lead metavanadate a portion of the lead is, however, frequently replaced by zinc.4... 

Vanadium Ferrocyanides.—Solutions of vanadates, when treated with potassium ferrocyanide, yield a precipitate of doubtful composition.1 The compound is insoluble in mineral acids of high concentration, and a method involving its precipitation has recently been suggested for the estimation of vanadium in steels.2... 

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