Vanadyl phosphates

Vanadyl phosphate (VOPO4 2H2O), a layered material containing Lewis and Brpnsted acid sites, was also tested as an acid catalyst in the dehydration of fructose to HMF (Scheme 7) [76]. These catalysts afforded HMF with a selectivity of 80% at 46% conversion of fructose. Other catalytic systems, obtained by partial substitution of groups with trivalent metals (Fe ", Cr, Ga, Mn, Al, were also investigated. It has been shown that when Fe-substituted vanadyl phosphate was employed a selectivity of 90% to HMF was obtained at 38% conversion without the formation of secondary products such as levuUnic and formic acid. This catalyst was also proved to be efficient for the conversion of inuUn into HMF with the same selectivity as with fructose. 

A third class of solids, which were tested as catalysts for carbohydrate dehydrations are inorganic phosphates. In a comparative study including vanadyl phosphate (VOPO4 2H2O) and partially metal-substituted vanadyl phosphates xPC>4 2H2O, M being Cr, Mn, Fe, A1 and Ga), it was... 

The evolution of the structure of four vanadyl phosphate hemihydrates has been studied and then used as catalysts for n-butane oxidation using an in-situ Raman cell and MAS-NMR. The catalytic performance for maleic anhydride... 

Vanadyl Phosphates, V02.P205.3H20 and 2VO2.3P2O5.10H2O, are prepared in blue needles by the action of hypovanadic oxide on phosphoric add.2... 

J. J. Berzelius25 said that when vanadyl phosphate, mixed with some sugar, is heated, the grey, porous mass which is formed can be pressed together when it has the appearance and lustre of graphite. It is considered to be an impure... 

Selective oxidation materials fall into two broad categories supported systems and bulk systems. The latter are of more practical relevance although one intermediary system, namely vanadia on titania [92,199-201], is of substantial technical relevance. This system is intermediary as titania may not be considered an inert support but rather as a co-catalysts [202] capable of, for example, delivering lattice oxygen to the surface. The bulk systems [100, 121, 135, 203] all consist of structurally complex oxides such as vanadyl phosphates, molybdates with main group components (BiMo), molybdo-vanadates, molybdo-ferrates and heteropolyacids based on Mo and W (sometimes with a broad variation of chemical composition). The reviews mentioned in Table 1.1 deal with many of these material classes. 

Vanadyl Phosphate Catalysts. — For the oxidation of C4-hydrocarbons to maleic anhydride, vanadyl phosphate catalysts with a variety of V P ratios and different additives have been proposed. Nakamura etal.123 observed for V P = 1 2, an average oxidation number of four for vanadium, highly aggregated vanadium ions and a high selectivity. Varma and Saraf124 also studied this reaction and on the basis of kinetic results propose a two-stage redox mechanism. They also concluded that maleic anhydride is hardly oxidized to carbon oxides, which are mainly formed in a side reaction from the original... 

Carlini, C., Patrono, P, Galletti, A. M. R., and Sbrana, G., Heterogeneous catalysts based on vanadyl phosphate for fructose dehydration to 5-hydroxymethyl-2-furaldehyde. Appl Catalysis A-Generul 2004,275 (l-2), 111-118. 

Vanadyl phosphates (VPO) and multiple component molybdate (MCM) are good examples of catalysts, and alpha alumina, amorphous silica and alumino-silicates are good examples of catalyst supports that can be fabricated in the form of 45 to 150 im diameter spray dried porous spheres with attrition resistance improved by a relatively thin peripheral layer rich in amorphous silica, amorphous alumina, or phosphorus oxides. The hard phase component or precursor is selected in each case so that it will not interfere with the catalytic performance of the catalyst. 

As an example, the precursor to the vanadyl phosphate catalyst was prepared following a method (1) based on reference (3). The MCM... 

Figure 4. Micrographs of the cross section of a vanadyl phosphate porous microsphere with 10% amorphous silica obtained by electron probe microanalysis (EPMA). Left backscattered electron image showing average atomic number across the specimen. Right X-ray image showing silicon distribution.

VPD route two-step preparation of V0EIP04 iiH20 from the reduction of vanadyl phosphate dihydrate (V0P04-2H20) with alcohol... 

Paramagnetic cations can give a large contact or psendo-contact shift and may broaden the P resonance. Chemical shifts of np to 1650 ppm have been found in vanadyl phosphates and nsed to estimate the magnetic exchange constants between vanadyl electronic spins. ... 

Evidence for the formation of vanadyl-phosphate complexes in aqueous solution relevant for physiological systems has been obtained from electron paramagnetic... 

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