Vanadium pentoxide structure

Figure 3.25 Mechanical twinning in vanadium pentoxide, V205 (a) the formation of needlelike twins at the tip of reduced oxide and (b) the idealized structure of the twin. Arrows in (a) represent the direction of shear forces.

Vanadium pentoxide has been investigated for 30 years ° ° it has a layered structure with weak vanadium—oxygen bonds between the layers and is now known to react by an intercalation mechanism 40,85 + V2O5 = LLV2O5. 

Figure 8. (a) Structure of the two-layer structure found in xerogel, and (b) comparison of the electrochemical behavior of the crystalline, xerogel,ct>-phase, and aerogeh forms of vanadium pentoxide. 

Enjalbert, R. and J. Galy. 1986. A refinement of the structure of vanadium pentoxide. Acta Cryst. C42 1467-1469. 

Galy, J. 1992. Vanadium pentoxide and vanadium oxide bronzes — structural chemistry of single (S) and double (D) layer MxV205 phases. J. Solid State Chem. 100 229-245. 

Fig. 25. A1 ternative toluene chemisorption systems involving the bipyramidal surface cluster of vanadium pentoxide. The structures (a, c, e, g, i) represent molecularly adsorbed toluene, while the remaining systems (b, d, f, h) model the dissociative adsorption, with two methyl hydrogens chemically bonded to the surface oxygens at the pyramid bases. Asterisks indicate positions which give rise to unstable MEC. The three atoms of the parallel complex (i), marked with an arrow, denote the extra instabilities appearing when the closed-system constraint (d N = 0) is imposed. The results are taken from Ref. 8. At each diagram the (I, E) stability diagnosis is also indicated (see Fig. 24)...

Fig. 34 shows the volume structure of vanadium-pentoxide [15]. The layered structure of the material is quite obvious and its electronic structure has been discussed in detail on the basis of diffraction data and theoretical investigations. 

The oxide V5O13 containing and is thought to play an important part in the action of vanadium pentoxide catalysts used in the oxidation of SO2 to SO3 and of naphthalene to phthalic anhydride. Its structure has been described in Chapter 5. 

Binary vanadium-titanium oxide catalysts with various ratios of vanadium oxide and titania, as well as individual oxides of vanadium and titanium were examined in oxidation of P-picoline. Nicotinic acid, 3-pyridinecarbaldehyde, and CO2 were the reaction products over all the catalysts. The binary catalysts and individual vanadium oxide were highly selective for nicotinic acid, the most effective in P-picoline oxidation were the samples containing 20% and more of vanadium pentoxide. A regular stacking of crystallites of V2O5 and Ti02 was found to be the characteristic feature of the structure of the most effective compositions. 

The specific surface area of vanadium pentoxide coated membrane was 1.1 m /g, and the average pore diameter of it, measured by nitrogen adsorption, was 30A. Macro pores identified by mercury intrusion did not exist, and the porosity was approximately 9%. From results of isotherm adsortion-desorption curve,as shown in Fig.2, V2O5-coated membrane has slit-shaped pore structure. Hence the pores mostly exist between the V2O5 layers, and the surface of those are nearly non-porous. 

Monti, D., Reller, A., and Baiker, A., Methanol oxidation on K2SO4—promoted vanadium pentoxide activity, reducibility, and structure of catalysts, J. Catal. 93 360-367 (1985). 

We now consider a quite different type of distortion, a good example of which occurs in the structure of vanadium pentoxide, V206 (27). The environment of the V6+ ion is illustrated in Fig. 24. Each V6+ ion has five... 

Ortho-xylene may be oxidized directly by air in vapor phase over vanadium pentoxide catalysts under conditions resembling those used in oxidation of naphthalene to phthalic anhydride. The stability of the cyclic anhydride structure of phthalic anhydride at the temperatures required and in the presence of oxidizing conditions is, of course, the distinctive feature. Since the oxidation of o-xylene to phthalic anhydride requires the theoretical interaction of only six atoms of oxygen relative to the nine required by naphthalene, the amount of heat generated per unit of product is less, and the volume of diluent gases in the product stream may be lower. Because of decreased formation of quinones and color bodies, product purification should be easier. Very little is available by way of information relative to commercial operating conditions. Some laboratory results of early work showed a maximum conversion to total acids of 18.2 per cent when commercial xylene was oxidized in vapor phase over unfused vanadium oxide catalyst. Recent work with o-xylene showed a conversion of 42.7 per cent to phthalic anhydride over unfused vanadium oxide catalyst and conversions up to 61.7 per cent to phthalic anhydride plus fi.6 per cent to maleic... 

In this section, we consider the case of solutions of rigid or semi-flexible polymers which display one or several liquid crystalline phases in a given range of concentration. The main control parameter is not flie temperature as is the case for thermotropic LCPs but rather the concentration of polymer in the solvent. There are many different kinds of lyotropic LCPs. Some are synthetic like Kevlar which has become a very important structural material with mechanical properties comparable to those of steel. Some are natural like the Tobacco Mosaic Virus and like DNA which shows a nematic and a hexagonal phase. Some are mineral like the vanadium pentoxide ribbons. In the next section, we shall first describe the lyotropic system which is probably best known, namely the tobacco mosaic virus. 

Another example of catalysts that undergo structural changes during reaction are catalysts that act by a redox mechanism, such as vanadium pentoxide used for partial oxidations. As shown by Mars and Van Krevelen [12], the catalyst provides the oxygen needed for the reactions, and it becomes reduced to a lower-valence oxide in the process ... 

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