Binary vanadium systems

In the present chapter, which deals with theoretical concepts applied to vanadium and molybdenum oxide surfaces, we will restrict the discussion to binary oxide systems. So far, mixed metal oxide systems have not been studied by quantitative theory. Theoretical methods that have been used to study oxide surfaces can be classified according to the approximations made in the system geometry where two different concepts are applied at present, local cluster and repeated slab models. Local cluster models are based on the assumption that the physical/chemical behavior at selected surface sites can be described by finite sections cut out from the oxide surface. These sections (surface clusters) are treated as fictitious molecules with or without additional boundary conditions to take the effect of environmental coupling into account. Therefore, their electro-... 

Fig.4 shows the selectivities for the reaction products and the rate of oxidation of P-picoline against composition of the vanadium-titania system. All the binary vanadium-titania catalysts and the individual vanadium oxide reveal high selectivities for nicotinic acid. The selectivity for nicotinic acid increases from 75 to 90% and the rate of p-picoline oxidation increases by three times as the concentration of V2O5 increases from 5 to 20%, no further... 

Fig.4. Rate of conversion of P-picoline (1) and selectivities for nicotinic acid (2), 3-pyridinecarbaldehyde (3) and CO2 (4) versus composition of the binary vanadium-titania system. Reaction temperature is 250°C. Conversion of P-picoline is 45%.

For the polymerization of cyclobutene, Natta and coworkers [37] reported binary catalytic systems containing titanium, vanadium, chromium, and tungsten to be the most active, those of molybdenum less active, and systems derived from cobalt, iron, manganese, and uranium totally inactive. Catalysts based on vanadium and chromium yield preferentially polycyclobutylene by addition polymerization, those with molybdenum and tungsten give polybutenamer by ring-opening... 

It may now be observed that the binary system of oxygen with Ti (as those of other metals close to Ti in the Periodic Table such as vanadium) is very complex and contains a high number of compounds. Many of these have rutile-related structures. For the Ti-0 region around the 50 at.% composition, with NaCl-type structure, see Fig. 3.38. 

In contrast to the aforementioned binary oxides, V2Os has a stronger oxidation power and is able to attack hydrogen attached to the aromatic nucleus. Sometimes attention is drawn to the importance of a layer structure in the catalyst or to geometric factors (e.g. Sachtler [270]). Unexpectedly, however, very effective vanadium-based catalysts exist which operate in the molten state, indicating that a fixed structure is not important. The catalytic activity of molten oxide phases seems to occur exclusively in the oxidation of aromatic hydrocarbons over V2Os-based catalysts, such systems have not been reported for the selective oxidation of olefins. 

Other common anode materials for thermal batteries are lithium alloys, such as Li/Al and Li/B, lithium metal in a porous nickel or iron matrix, magnesium and calcium. Alternative cathode constituents include CaCr04 and the oxides of copper, iron or vanadium. Other electrolytes used are binary KBr-LiBr mixtures, ternary LiF-LiCl-LiBr mixtures and, more generally, all lithium halide systems, which are used particularly to prevent electrolyte composition changes and freezing out at high rates when lithium-based anodes are employed. 

The development of implanted medical defibrillators required a high-rate, long-life battery system. In defibrillators, the CFx is used in combination with silver vanadium oxide (SVO) cathode materials [17]. A binary mixture of CFx and SVO are combined to form the cathode, giving the best features of SVO and CFx. Compared to CFx, the SVO has superior pulse current capability, but lower energy storage capability. The cell reactions are given in Equations 10.7 and 10.8. 

The most studied systems for oxidative propane upgrading are vanadium [2], vanadium-antimony [3], vanadium-molybdenum [4], and vanadium-phosphorus [5] based catalysts. Another family of light paraffin oxidation catalysts are molybdenum based systems, e.g. nickel-molybdates [6], cobalt-molybdates [7] and various metal-molybdates [8-9]. Recently, we investigated binary molybdates of the formula AM0O4 where A = Ni, Co, Mg, Mn, and/or Zn and some ternary Ni-Co-molybdates promoted with P, Bi, Fe, Cr, V, Ce, K or Cs [10-11]. A good representative of these systems is the composition Nio.5Coo.5Mo04 which was recently selected for an in depth kinetic study [12] and whose mechanistic aspects are now further illuminated here. 

At. M. Oxidation activity and acid-base properties of tin dioxide-based binary catalysts. I. Tin dioxide-vanadium pentoxide system. Journal of Catalysis 1975 40, 318-326. 

In the accepted reaetion scheme, temperatures of some invariant equilibria in the binary systems were corrected in accordance with the accepted binary phase diagrams. Invariant equilibria, that included subcarbides of vanadium were omitted due to the absence of experimental data on the influence of alloying with Fe on the ordering of VCy and V2C carbides. 

Spectrophotometric determination of the binary complex Spec determination of the violet complex in acidic medium Extraction-spectrophotometric determination of the system V(V)-3,5-dinitrocatechol (DNC)-brilliant green chelate complex Extraction with H-butanol and spec X = 390 nm of a ternary complex (vanadium oxine H-butanol = 1 2 2)... 

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