Vanadium promoted

The vanadium-promoted epoxidation method has proved to be valuable in synthetic routes leading to dl-Ci8 Cecropia juvenile hormone20 and lasalocid A.24 The mechanism of vanadium-mediated epoxidation has been elucidated25 but an evaluation of the use of other organometallic compounds as epoxidation reagents is required.26... 

Important information on reaction mechanisms and on the influence of promoters can be deduced from temperature programmed reactions [2], Figure 2.8 illustrates how the reactivity of adsorbed surface species on a real catalyst can be measured with Temperature Programmed Reaction Spectroscopy (TTRS). This figure compares the reactivity of adsorbed CO towards H2 on a reduced Rh catalyst with that of CO on a vanadium-promoted Rh catalyst [13]. The reaction sequence, in a simplified form, is thought to be as follows ... 

The highest (iBu)2NH yield (72 %) was obtained a conversion level of 92% and at reaction parameters P=13 bar, T=240°C, WHSV=1.0 g/g h, NH3/iBuOH= 1.7, H2/NH3= 1.9. In conclusion, a secondary amine yield above 70 % can be was obtained in fixed bed reactor using vanadium promoted Raney nickel catalyst without recycling unconverted alcohol. In order to describe the conversion of alcohol, as well as the yield and selectivity of diisobutylamine in the function process parameters, experiments were carried out and results were evaluated according to orthogonal factorial design (6,7). 

Fickl, H., AJ. Theron, H. Grimmer, J. Oommen, GJ. Ramafi, H.C. Steel, S.S. Visser, and R. Anderson. 2006. Vanadium promotes hydroxyl radical formation by activated human neutrophils. Free Radic. Biol. Med. 40 146-55. 

Dopant, optimal amount expressed as a ratio to vanadium Promotional effect on conversion C and MA selectivity S for the undoped and (doped) catalysts expressed as % Reasons for promotion Reference... 

Vanadium. A residual oil was desulphurized (673 K, 115 atm) with a non-stoicheiometric vanadium sulphide (S/V, 0.8-1.8) formed in situ from VS4 Vanadium sulphide catalysts have been prepared by in situ sulphiding of vanadium complexes, e.g., bis(acetylacetonato)oxovanadium(IV), dissolved in crude petroleum.Vanadium compounds occurring in heavy oils have been activated as desulphurization and demetallization catalysts by treatment with triethylaluminium. Catalysts consisting of vanadium promoted by nickel can be prepared in situ by deposition of the metals from heavy crude oils. Ni-V hds and hdm catalysts on silica or carbon have been claimed. 

Molybdenum and vanadium promote nitrogen fixation by A. chroococcum,A. vinelandii and Bac. amylobacter, [in the case of] molybdenum up to the 100-fold of the amount accomplished in the absence of theses elements hy Azotobacter. From this it is concluded that without molybdenum or vanadium there is no possibility for any appreciable nitrogen fixation. ... 

These processes were observed in many experiments with Ti02 powder in a nitrogen atmosphere in the presence of water adsorbed on the Ti02 surface. Addition of small amounts of a-Fc203 to Ti02 essentially increases the reaction rate. Nitrogen is also known to be reduced with water to NH3 on Fc203 or vanadium-promoted hydrous ferric oxide. 

H3P02-modified Pt Catalysts in Presence of Vanadium Promoters... 

The over-all reaction with vanadium promoter was usually faster than without, whereas other successful promoters led to a somewhat slower reaction. Products obtained with efficient promoters were whiter (cleaner) than those without. 

Catalytic hydrogenations of aromatic nitro compounds with a stable hydroxylamine intermediate often have two different kinetic phases hydrogen uptake is rapid up to ca 60 %, then distinctly slower in the second phase. This means that reduction of the hydroxylamine to the aniline, formally a hydrogenolysis, is difficult in these cases. In the presence of the promoters discussed in Section 8.5.4.3, the second phase is less pronounced or disappears. This suggests a mechanism which could be called catalytic by-pass (see Figure 4). Experiments in the absence of hydrogen indicated that the vanadium promoters catalyze the disproportionation to give aniline and the nitroso intermediates that re-enter the catalytic cycle. As a consequence, the hydroxylamine does not accumulate and aniline formation is accelerated. 

The chromium-promoted catalyst was the most effective for destroying the chlorinated hydrocarbons, with 85% conversion at 450°C. It was evident that the chromium catalysts were most active, with vanadium the next active showing a maximum conversion of 53%. The other catalysts did not achieve 50% conversion. Further studies with the most active chromium and vanadium promoters showed that in general the activity increased as the loading of chromium and vanadium increased. 

The additive elements used to enhance the performance of the Fe-Sb-0 catalyst either enter the iron antimonate rutile phase to form a solid solution (49,50) or they form separate rutile phases (44). The promoter elements that produce the best performing iron antimonate-based ammoxidation catalysts are copper, molybdenum, tungsten, vanadium, and tellurium. Copper serves as a structural stabilizer for the antimonate phase by forming a rutile-related solid solution (23). Molybdenum, tungsten, and vanadium promote the redox properties of iron antimonate catalysts (51). They provide redox stability and prevent reductive deactivation of the catalyst, especially under conditions of low oxygen partial pressure (see above). The tellurium additive produces a marked enhancement of the selectivity of iron antimonate catalyst. How the tellurium additive functions to increase selectivity is not clear, but the presumption is that it must directly modify the active site. In fact, it is likely that it can actually serve as the site of selective oxidation because in its two prevalent oxidation states Te + and Te +, tellurium possesses the requirements for the selective (amm)oxidation site, a-hydrogen abstraction, and 0/N insertion (see below). 

Nickel and, to a lesser extent, vanadium promote the production of molecular hydrogen during catalytic cracking of gas oil. The metals are deposited on the catalyst, and unless they are deactivated—for example by adding antimony—hydrogen production from FCCU feed is enhanced. This effect is... 

Garcia, T., Solsona, B., Cazorlaamoros, D., Linaressolano, A., and Taylor, S. (2006) Total oxidation of volatile organic compounds by vanadium promoted palladium-titania catalysts comparison of aromatic and polyaromatic compounds. Appl Catal B Environ., 62 (1-2), 66-76. 

Primary Reactions. The basic chemistry used in the Sulfolin process parallels that employed in Stretford solutions, except for the use of an organic nitrogen vanadium promoter instead of the ADA oxygen carrier (Heisel and Maiold, 1987). 

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