V2O5 Oxides

4 V2O5 Oxides. - Supported V2O5 oxides are extremely important industrial catalysts for environmental pollution control, and are used in catalytic scrubbers for SO2 oxidation and NO reduction. During the operation of the catalyst (usually at 400-600 °C) in the SO2 oxidation reactions, pyrosulfate melts are formed in the pores of the catalysts, and V2O5 can dissolve in these melts forming vanadium oxo-sulfate complexes  

While this work illustrates the importance of examining these catalysts under in situ conditions, vital clues to the nature and symmetry of the vanadium ions can nevertheless be obtained through very careful analysis of the EPR spectra at low temperatures. This was demonstrated by Dyrek et al. who studied the changes to the oxidation state and coordination environment of vanadium in V2O5 in the presence of O2-SO2 mixtures. By calculating the crystal field parameters (A and 5) from the EPR spectra using the equations fify = — 4A./A) 

Numerous studies have appeared in the past two years on the eharacterisation of supported vanadium oxides under statie eonditions. EPR eharaeterisation at X- and Q-band frequencies was earned out on a fresh and used V205-W03/Ti02 catalyst. In both cases, evidence was found for the existenee of ions in eluster-like arrangements in two different sites, eorresponding to VO + in axially distorted octahedral symmetry ( j = 1.923, = 1.983, Aj = 

Ay = 80.4 G for the used catalyst). While traces of bulk TP+ eations were observed ( j = 1.965 and gry = 1.970) there was no evidenee for bulk ineorpor-ation of V + into the titania matrix. By eomparison, at least three different families of ions were identified by EPR in V20s/Ti02 eatalysts prepared by a sol-gel method. Two kinds of isolated ions were found and ascribed to sites 

A more general study of the redox properties of the V2O5 oxide as a function of the metal oxide support (AI2O3, MgO, Mg-Al-hydrotalcite and Mg-Al-Spinel) was carried out using EPR. The different reducibilities of the vanadium species were related to the acid-base character of the metal oxide support. While was easily reduced to on acidic metal oxides, the reduction was hindered on basic supports, as EPR evidenced the preferential formation of from 

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Makgwane, P.R. and Ray, S.S. (2014) Efficient room temperature oxidation of cyclohexane over highly active hetero-mixed WO3/V2O5 oxide catalyst. Catal Commun., 54, 118-123. 

Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

Vanadium dioxide, VO2 is dark blue (V2O5 plus SO2) but is readily reduced further to Vo.i86-V,.6a. VO2 gives the (VO) ion with acids and vanadates(IV) with alkalis and as mixed metal oxides. 

Vanadium pentoxide, vanadium(V) oxide, V2O5, is the most important compound in this oxidation state. It is a coloured solid (colour due to charge transfer, p. 60), the colour varying somewhat (red -> brown) with the state of subdivision it is formed when vanadium (or some of its compounds) is completely oxidised, and also by heating ammonium vanadate)V) ... 

The alkyl derivatives of thiazoles can be catalytically oxidized in the vapor phase at 250 to 400°C to afford the corresponding formyl derivatives (21). Molybdenum oxide, V2O5, and tin vanadate are used as catalysts either alone or with a support. The resulting carbonyl compounds can be selectively oxidized to the acids. 

Silicon Reduction. The preparation of ferrovanadium by the reduction of vanadium concentrates with ferrosiUcon has been used but not extensively. It involves a two-stage process in which technical-grade vanadium pentoxide, ferrosiUcon, lime, and fluorspar are heated in an electric furnace to reduce the oxide an iron alloy containing ca 30 wt % vanadium but undesirable amounts of siUcon is produced. The siUcon content of the alloy is then decreased by the addition of more V2O5 and lime to effect the extraction of most of the siUcon into the slag phase. An alternative process involves the... 

Vanadium Carbide. Vanadium pentoxide [1314-62-17, V2O5, or vanadium trioxide [1314-34-7] VO3, are the most satisfactory oxides for the preparation of VC. Vanadium pentoxide is best prepared by igniting chemically pure ammonium vanadate [7803-55-6] NH VO, in the presence of moist oxygen to avoid reaction with nitrogen V2O3 is obtained by reduction of V2O3 with hydrogen (see Vanadium compounds). 

Catastrophic oxidation requires the presence of Na2S04 and Mo, W, and/or V. Crude oils are high in V ash will be 65% V2O5 or higher. V can be alloyed in metal. A galvanic cell is generated ... 

Vanadium pentoxide, VjOj, is used as a eatalyst in the oxidation of sulfur dioxide. The meehanism involves oxidation-reduetion of V2O5 that exists on the support at operating eonditions in the molten state. The meehanism of reaetion is ... 

COBr2 has recently been shown to be a useful general brominating reagent for the preparation of d- and f-block bromides and oxide bromides.Thus, when V2O5 is heated with an excess of COBr2 in a sealed Car-ius tube at 125°C for 10 days, a quantitative yield of VOBr2 is obtained by a reaction that is driven thermodynamically by... 

Other catalyst systems such as iron V2O5-P2O5 over silica alumina are used for the oxidation. In the Monsanto process (Figure 6-4), n-butane and air are fed to a multitube fixed-bed reactor, which is cooled with molten salt. The catalyst used is a proprietary modified vanadium oxide. The exit gas stream is cooled, and crude maleic anhydride is absorbed then recovered from the solvent in the stripper. Maleic anhydride is further purified using a proprietary solvent purification system. ... 

Benzene oxidation is the oldest method to produce maleic anhydride. The reaction occurs at approximately 380°C and atmospheric pressure. A mixture of V2O5/MO3 is the usual catalyst. Benzene conversion reaches 90%, hut selectivity to maleic anhydride is only 50-60% the other 40-50% is completely oxidized to C02 °... 

Currently, phthalic anhydride is mainly produced through catalyzed oxidation of o-xylene. A variety of metal oxides are used as catalysts. A typical one is V2O5 -1- Ti02/Sb203. Approximate conditions for the vapor-phase oxidation are 375-435°C and 0.7 atmosphere. The yield of phthalic anhydride is about 85% ... 

Figure 10.8. Turnover frequency of S02 catalytic oxidation [mol S02 (conv.)/mol V2O5/S] vs. working electrode polarization for the (1) 17 mol % V2Os - 83 mol % K2S207 catalyst at 460°C and for (2) 10 mol % V2Oj - 90 mol% K2S207 catalyst.12 Reproduced by permission of the Electrochemical Society.

A related approach is to interface an industrial promoted catalyst with a solid electrolyte (Fig. 12.2). In this case the bulk of the commercial catalyst must be conductive. This concept has been already demonstrated for the case of NH3 synthesis on Fe-based promoted commercial catalysts (BASF S6-10 RED)16 and for the case of SO2 oxidation on V2O5-K2S2O7 based catalysts (Haldor-Topsoe VK-58).17... 

Phthalic anhydride will, in the presence of the V2O5 catalyst of Example 9.1, undergo complete oxidation with A772 = — 760kcal/mol. Suppose the complete oxidation is pseudo-first-order in phthalic anhydride concentration and that ln( k//) = 12.300—10,000/T. 

An alternative route to phthalic anhydride is the partial oxidation of naphthalene. The heat of reaction is — 430 kcal/mol. This reaction can be performed using a promoted V2O5 catalyst on silica, much like that considered in Example 9.1. Suppose In(fik) = 31.6800—19,100/T for the naphthalene oxidation reaction and that the subsequent, complete oxidation of phthalic anhydride follows the kinetics of Problem 9.3. Suppose it is desired to use the same reactor as in Example 9.1 but with a,>, = 53g/ m. Determine values for and T aii that maximize the output of phthalic anhydride from naphthalene. 

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