Crystal vanadium oxides

Vanadium oxide dichloride, VOCI2. Green crystals VOCI3 plus H2. 

Vanadium in the feed poisons the FCC catalyst when it is deposited on the catalyst as coke by vanadyl porphydrine in the feed. During regeneration, this coke is burned off and vanadium is oxidized to a oxidation state. The vanadium oxide (V O ) reacts with water vapor in the regenerator to vanadic acid, HjVO. Vanadic acid is mobile and it destroys zeolite crystal through acid-catalyzed hydrolysis. Vanadic acid formation is related to the steam and oxygen concentration in the regenerator. 

The introduction of microwave pr ents an excellent new option for the synthesis of VOPc from vanadium oxide, dicyanobenzene, and ethylene glycol. In the present study, the effectiveness of synthesizing crude VOPc liom vanadium oxide and dicyanobenzene rmder the two synthetic methods was investigate by comparing reaction temperatures. Also, the preparation of fine crystal VOPc was investigated from the crude VOPc synthesized at... 

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

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. 

M. C., Moulijn, J.A., Medema, J., de Beer, V.H.J. and Gellings, P.J. (1980) Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports. J. Phys. Chem., 84, 2783. 

Andersson, S. 1965. Hydrothermally grown crystals of silver vanadium oxides bronzes. Acta Chem. Scand. 19 269-270. 

The calculation of the electronic states of lithium vanadium oxide is carried out using cluster models taken from bulk crystal. The model clusters which are... 

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

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... 

So far, theoretical studies on vanadium oxide surfaces have focused exclusively on single crystal surfaces which are described by low Miller indices and are believed to be energetically favorable. These surfaces are most easily accessible by theory due to their relatively simple geometry although their relevance as to catalytic activity has been doubted. 

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.

Figure 5 shows the fused 10 mole % 9 1 precursor both freshly prepared, after reduction with at 450 C and after treatment with H SO and NH, respectively. From the fact that needle-like crystals appear on the TIO surface after reduction, it can be concluded that the vanadium oxide phase in the precursors covers the TiO particles. This was also the conclusion drawn from quantitative ESCA data. 

According to ESCA measurements carried out with vanadium oxide, consistent with the data presented in [12], the Ols characteristic of On oxygen species is very close to the V=0 doubly bonded oxygen atoms exposed at the surface of (010) planes of V2O5 crystals. The oxygen species with Ols characteristic of Oi do not exist at the surface of individual main components of catalysts A,B - vanadia, molybdena, or exist in small concentration at the surface of magnesia or TM. They... 

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