Vanadium oxide , crystal structure

Wadsley A.D. Crystal chemistry of non-stoichiometric pentavalent vanadium oxides crystal structure of Li ,V 0. ActaCryst. 1957 10 261-67. 

A colorless mineral known as corundum (composed of aluminum oxide) is colorless. A red variety of corundum known as ruby, a precious stone, owes its color to impurities of chromium within the crystal structure of corundum. Blue and violet varieties of corundum are classified as sapphires, the blue being the result of iron and titanium impurities, and the violet of vanadium impurities within the corundum crystal structure. Another colorless mineral is beryl (composed of beryllium aluminum silicate) but blue aquamarine, green emerald, and pink morganite, are precious varieties of beryl including different impurities aquamarine includes iron, emerald chromium and vanadium, and morganite manganese. 

Simple Binary and Related Compounds.—Oxides. The information presently available concerning the crystal structures and properties of vanadium oxides has been tabulated. 

Nitriloacetic acid reacts with vanadium-(m). -(iv), or -(v) oxides to form oxovanadatranetrionic acid (38). The crystal structure of [VO(CjQHgNO)2] (CjgHgNOH = 2-methyl-8-quinolinol) has shown that the vanadium atom has a five-co-ordinate trigonal-bipyramidal environment, with three oxygen atoms in the equatorial plane and the two nitrogen atoms of the bidentate ligand in the apical positions. The optimum conditions for the formation of a 1 2 2 vanadium(iv)-morin-4-aminoantipyrine system have been described as pH 5, a tenfold excess of morin (39), and a 3300-fold excess of 4-amino-antipyrine. ... 

Since little is known about crystal structures of the low-temperature mked oxides of niobia, it is difficult to explain from a theoretical point of view the good results obtained for doping with vanadium or chromium. It appears that the vanadium and chromium are present in the catalyst in a unique environment, which makes... 

The influence of different preparation methods upon the structure and reactivity of supported vanadia catalysts has recently been investigated by several laboratories.55 58 These studies concluded that the same surface vanadia species forms on a specific oxide support independent of the preparation method, even when starting with V205 crystals. The reason for this phenomenon is that vanadium oxide spontaneously disperses on oxide supports to form surface vanadia species, which is schematically depicted in Figure 7. 

Point defects in the form of cation vacancies () were introduced by Aykan et al. (93-95) into molybdates, tungstates, and vanadates with scheelite-type crystal structures. The authors studied the catalytic properties of more than 30 scheelite-structure phases represented by the formula A1 x< xM04 (M = molybdenum, tungsten, and/or vanadium and A may include Li, Na, K, Ag, Ca, Sr, Ba, Cd, Pb, Bi, and/or arare earth element in quantities appropriate to achieve charge balance for the normal oxidation states). It was found that the defects can be introduced... 

Andersson, S. 1965. The crystal structure of a new silver vanadium oxide bronze, Agi xV205 (x. approx. 0.32). Acta Chem. Scand. 19 1371-1375. 

Recently, Carreon and Guliants reported novel hexagonal, cubic and lamellar VPO phases, which displayed improved thermal stability, desirable chemistries (i.e. the P/V ratios and vanadium oxidation states), and pore structures for the partial oxidation of n-butane [143-145]. These novel VPO phases displayed the selectivities to maleic anhydride up to 40 mol. % at 673K at 10 % n-butane conversion [146]. A conventional organic VPO catalyst containing well-crystallized vanadyl(IV) pyrophosphate, the proposed active and selective phase for n-butane oxidation to maleic anhydride, displayed the selectivities to maleic anhydride 50 mol. % under the same reaction conditions. The low yields observed for mesoporous VPO catalysts confirmed the critical role of the vanadyl pyrophosphate phase (VO)2P207 in catalyzing the oxidation of -butane to maleic anhydride. Therefore, the amorphous nature of the mesoporous VPO... 

Single crystals of vanadium oxide can be classified in their geometric structure, apart from their lattice definition by lattice and lattice basis vectors, by the occurrence of specific elementary VO building units. All single valency oxides are characterized by a common octahedral VOe unit. The different crystal lattices differ by the distortion of the octahedral units (as a result of actual V-0 distances and O-V-O angles) as well as by the connectivity of the units in the... 

Figure 1.41. The three-dimensional view of the crystal structure of tmdW %02o (vanadium oxide layers and nitrogen atoms from tma molecules) with added symmetry elements. The space group symmetry of the material is C2/m.

The selective oxidation of methanol to give formaldehyde is in practice performed in two different processes, one using metallic silver, the other using iron molybdate as catalyst. Vanadium oxide has been shown to be a good selective catalyst in a variety of oxidation processes (refs. 1-2) and we have previously shown that it is also selective for methanol oxidation (refs. 3-5) when the V Og is applied as a very thin layer (monolayer) on different supports the support can have a significant influence on the activity and selectivity of these monolayer catalysts, as was shown by Roozeboom (ref. 6). In a previous paper (ref. 5), it was shown that both the type of support (A Og or TiC ) and the crystal structure of the TiO have an influence on the selectivity of the catalyst for the production of formaldehyde in general, production of the formaldehyde increases with a decrease in the reducibility of the vanadia. 

Vanadium. Vanadyl complexes of the three ligands 14, 24, and 28 were prepared from vanadyl sulfate and the metal-free ligands. They have the expected spectroscopic properties, and this is confirmed by the X-ray crystal structure of the vanadyl complex of 24, which is shown in Fig. 23(a) and has metal-donor bond distances in the expected range. In terms of reactivity, these complexes are rather unspectacular. No haloperoxidase reactivity was observed, and oxidation of alkanes and alkenes is rather sluggish (138). This is not unexpected since with the pentadentate ligands there is no free site at the vanadium(IV) center for metal-substrate interaction. The same is true for the vanadium(V) oxo-peroxo complexes with tetradentate coordination of the pentadentate ligand. 

M.l. Khan, M. I. E.Yohannes, and D. Powell, Synthesis and characterization of a new mixed-metal-oxide framework material composed of vanadium oxide clusters x-ray crystal structure of (N2H5)2[Zn3V, V 6042(S04)(H20)i2]-24H,0 J. Chem. Soc., Chem. Com.,13 (1999). (b) M. I. Khan. 

The elements beryllium, magnesium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, molybdenum, silver, cadmium, tin, thallium, lead, and bismuth mainly occur in the crystal structures of rock-forming silicates and oxides of the common rocks in the Earths crust. These elements - with the exception of magnesium, iron, titanium, chromium, and zirconium - are trace elements in the minerals. They follow certain rules as reported by Goldschmidt (1954) in their ten-... 

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