Vanadium-based catalytic systems

Since the 1960s the syndiospecific chain-end controlled polymerization of propene in the presence of homogeneous vanadium-based catalytic systems has been known. For these systems, it has been well established by the work of Zambelli and co-workers that the polymerization is poorly regioselective and the stereoselective (and possibly syndiospecific) step is propene insertion into the metal secondary carbon bond with formation of a new secondary metal-carbon bond.133134... 

The Sharpless epoxidation proceeds poorly with homoallylic alcohols and some work has been directed towards the development of zirconium and vanadium-based catalytic systems capable of oxidising these substrates in an enantioselective... 

Vanadium-based catalytic systems for EP(D)M synthesis are comprised of a vanadium compound ( catalyst precursor ), a chlorinated aluminum alkyl ( cocatalyst ), and a chlorinated ester ( promoter ). Typical components of a vanadium-based catalytic system are the following ... 

Samiah, G., Bharadwaj, S. K., Dewan, A., Gogoi, A., and Bora, U. (2014). An efficient and reusable vanadium based catalytic system for room temperature oxidation of alcohols to aldehydes and ketones. Tetrahedron Lett., 55, 5029-5032. 

The vanadium-based catalyst systems deteriorate with time and decrease in the number of catalytic centers as the polymerizations progress. The rate of decay is affected by conditions used for catalyst preparation, compositions of the catalysts, temperature, solvents, and Lewis bases. It is also affected by the type and concentration of the third monomer. Additions of chlorinated compounds to the deactivated catalysts, however, help restore activity. Catalyst decay can also be overcome by continually feeding catalyst components into the polymerization medium. ... 

This review is a survey of the applications and properties of supported liquid phase catalysts (SLP). By a supported liquid phase catalyst is meant the distribution of a catalytically active liquid on an inert porous support and the behaviour of such systems raises many interesting questions on catalyst chemistry, mass transfer in catalysts and reactor design. It is noteworthy thou that such systems have been employed in the chemical industry for many decades - indeed for over a century in the Deacon process for obtaining chlorine from hydrogen chloride - and of almost equally respectable antiquity are the vanadium based catalyst systems used for sulfuric acid manufacture but the recognition of SLP catalysts as possessing features of their own is much more recent. 

The replacement of vanadia-based catalysts in the reduction of NOx with ammonia is of interest due to the toxicity of vanadium. Tentative investigations on the use of noble metals in the NO + NH3 reaction have been nicely reviewed by Bosch and Janssen [85], More recently, Seker et al. [86] did not completely succeed on Pt/Al203 with a significant formation of N20 according to the temperature and the water composition. Moreover, 25 ppm S02 has a detrimental effect on the selectivity with selectivity towards the oxidation of NH3 into NO enhanced above 300°C. Supported copper-based catalysts have shown to exhibit excellent activity for NOx abatement. Recently Suarez et al and Blanco et al. [87,88] reported high performances of Cu0/Ni0-Al203 monolithic catalysts with NO/NOz = 1 at low temperature. Different oxidic copper species have been previously identified in those catalytic systems with Cu2+, copper aluminate and CuO species [89], Subsequent additions of Ni2+ in octahedral sites of subsurface layers induce a redistribution of Cu2+ with a surface copper enrichment. Such redistribution... 

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. 

A third catalytic system was proposed more recently and based on vanadium aluminum oxynitrides (VALON) [30]. The maximum acrylonitrile yield reported was about 30%, but with acrylonitrile productivity four times higher than for V/ Sb/W/Al/O catalysts and one order of magnitude than for Mo/V/Nb/Te/O. Other companies have studied and developed proprietary formulations but, in general, catalytic systems belong either to the antimonates family (Rhodia, BASF, Nitto, Monsanto) [31-33] orto the molybdates family. 

Nevertheless, many vanadium-based catalysts and polymerisation systems comprising them have received much academic attention in the hope that they might provide models for heterogeneous catalysts and polymerisation systems, since the problems connected with surface properties and particle size were believed to have been overcome. It must be noted, however, that homogeneous vanadium-based catalysts appeared to be more complex than was thought. There is no decisive evidence on the structure of catalytic sites formed by reaction between the procatalyst and activator. 

Studies have also focused on vanadium-based asymmetric catalysts in addition to these photocatalytic systems. A catalytic achiral version of an oxidative coupling reaction was published in 1999 by Uang and co-workers (see Section 14.4.2) [70]. They developed an air-stable complex (VO(acac)2) that can be used in catalytic quantities in the presence of dioxygen as a re-oxidant. The promising results obtained led to an investigation of chiral versions of this reagent, and the initial reports document that such a reaction was possible with complexes... 

Later, they developed a catalytic method using the technology developed by Bolm et al. based on the use of chiral Schiff base-vanadium complexes. After extensive work optimizing the catalytic system, they found that the use of 0.25 equiv of the... 

Examples of homogeneous catalytic systems in propylene polymerization are very few. Zambelli et al. obtained syndiotactic polypropylene by working at low temperatures with catalytic systems based on some vanadium compounds and aluminum alkyls, while Giannini et al. were the first to prepare isotactic polypropylene with some benzyl derivatives of titanium or zirconium. 

Thus, results obtained with some vanadium based homogeneous catalytic systems have also been explained in this manner. Christman has examined polyethylene obtained in a completely homogeneous reaction system, since the catalytic system was soluble and the polymerization took place under such temperature conditions as to keep the polymer dissolved in the reaction medium. 

Cozewith and Ver Strate examined fractionation data of ethylene-propylene copolymers obtained with homogeneous or apparently homogeneous systems, based on vanadium compounds such as VCl and aluminum trialkyl, or VOCI3 and AKCjHjljCl. While some catalytic systems gave the expected narrow MWD with Q 2 and high composition uniformity concerning monomeric units distribution, others gave a wider composition distribution and multimodal and broader MWD with Q even >10. The authors attributed this last result to different active centres. 

Another widely studied area of homogeneous catalytic systems is based on vanadium compounds which, under specific conditions, polymerize propylene into a syndio-tactic polymer. 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

This catalytic system, as well as systems based on Mo/V/Te/Nb mixed oxides which have been developed by Mitsubishi (65), also represent an example of catalyst characterized by multifunctional properties. The rutile structure is the matrix to host vanadium ions as solid solutions, while the antimony oxide is present as a dispersed microcrystalline oxide. Vanadium is the component which is more active in paraffin conversion, while the high selectivity to the desired product is due to the presence of dispersed, separate phase, antimony oxide. 

The efficiency of zinc-chromium and vanadium-magnesium oxide catalysts in the reaction of butanediol dehydrogenation has been established. The optimum reaction conditions in butadione synthesis providing high yields and selectivity have been found. Experimental substantiation of principles for the purposeful synthesis of the catalytic systems mentioned above is considered. The catalysts were prepared based on these principles. 

Among known Ziegler-Natta catalytic systems catalysts on the base of V and Ti compounds combination with chloroaluminumalkyles are effective for ethylene and propylene copolymerization [176, 177]. It is particularly convenient to use systems on the base of vanadium compounds (tetrachloride, trichloroxide, triacetylacetonate) and diisobutylaluminum chloride. 

The 1,2-addition of a cyanide ion to a carbonyl compound to form a cyanohydrin is a fundamental carbon-carbon bond-forming reaction in organic chemistry, and has frequently been at the forefront of advances in chemical transformations. In 2000, Belokon and North developed a catalytic system based on a vanadium-salen complex (Scheme 9.1). The synthesis of vanadium(iv) complex 1 was accomplished by refluxing a mixture of the corresponding Schiff base with vanadium(iv) sulfate and pyridine in ethanol under an argon atmosphere. A very low catalyst loading of 0.1 mol% was employed to convert aromatic and aliphatic aldehydes to cyanohydrin silyl ethers 3 with enantioselectivities of 68-95% after 24 h. Further investigations... 

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