Vanadium sulfide

A high-nickel alloy is used for increased strength at elevated temperature, and a chromium content in excess of 20% is desired for corrosion resistance. An optimum composition to satisfy the interaction of stress, temperature, and corrosion has not been developed. The rate of corrosion is directly related to alloy composition, stress level, and environment. The corrosive atmosphere contains chloride salts, vanadium, sulfides, and particulate matter. Other combustion products, such as NO, CO, CO2, also contribute to the corrosion mechanism. The atmosphere changes with the type of fuel used. Fuels, such as natural gas, diesel 2, naphtha, butane, propane, methane, and fossil fuels, will produce different combustion products that affect the corrosion mechanism in different ways. 

The generation of H2 from H2S by visible light has also been suggested . The efficiency of this process is increased by the presence of sulfite. The latter removes the sulfur formed in the oxidation of HjS to yield thiosulfate. Substitution of RUO2 by RuS2 leads to an increased H2 yield H2 from H2S is also formed in vanadium sulfide dispersions loaded with RUO2 ... 

These data taken together suggest that vanadium is deposited on the catalyst in three successive forms. The initial vanadium which appears on the catalyst is primarily an isolated V02+ species, presumably associated with alumina defect sites. This is followed by the diamagnetic vanadium surface phase and finally by the vanadium sulfides. This progression is illustrated by the analysis of catalyst samples taken from different positions in a reactor which had been employed in a pilot-plant treatment of a petroleum residuum (Figure 4). Note that all of... 

Al-Shamma, E., Naman, S.A. 1989. Kinetie study for thermal production of hydrogen from H S by heterogeneous catalysis of vanadium sulfide in a flow system. Int J Hydrogen Energy 14 173-179. 

Namon, S.A., Aliwi, S.M., Alemara, K. 1986. Hydrogen-production from the splitting of H S by visible-light irradiation of vanadium sulfides dispersion loaded with RuOj. Int J Hydrogen Energy 11 33-38. 

Oxides Vanadium monoxide VO, gray solid vanadium trioxide V2O3, black solid vanadium dioxide VO2, dark blue solid vanadium pentoxide V2O5, orange to red solid. The last is the most important oxide formed by the ignition in an of vanadium sulfide, 01 othei oxide, 01 vanadium used as a catalyzer, e.g., the reaction SO2 gas plus oxygen of air to form sulfur tnoxide. and the oxidation of naphthalene by air to form phthalie anhydride. 

Vanadyl salen is readily converted at 100°C with H2S in the absence of a catalyst to a vanadium sulfide and a free organic ligand (or decomposition products). Vanadyl phthalocyanine is more stable with respect to ring attack and demetallation. Rates relative to catalytic reactions have not been measured. If VO-salen is an appropriate model of vanadium binding in asphaltenes, asphaltenic metals are more readily converted to sulfides under hydrotreating conditions than the porphyrinic metals. This suggests... 

Fig. 41. Proposed reaction mechanism and model of a vanadium sulfide surface site for hydrodemetallation (Takeuchi et al., 1985).

The catalysts used for processing heavy feedstocks inevitably deactivate with time due to accumulation of nickel and vanadium sulfides and carbonaceous residues (coke) on the catalyst. The former deposits have been studied intensely, in part because the metal deposits tend to accumulate near the surface of catalyst pellets, rendering the interior ineffective. Both metal sulfides and coke may contribute to loss of activity. 

The transition metal trichalcogenides MX3 (M = Ti, Zr, Hf, Nb, Ta X = S, Se) have been studied in some detail. All the trichalcogenides contain anion-anion bonding and consequently a redox competition exists between electron transfer to the metal center and electron transfer to the anions. The situation is the converse of the deintercalation of the thallium vanadium sulfides, where the competition is between oxidation of T1+ cations and that of the metal sulfur framework. 

A number of vanadium sulfide phases, ranging from VS4 to V3S, have been reported, although few have been well characterized and some may not exist at all. The structures, where known, are often complicated and difficult to describe. 

A compound identified as iron vanadium sulfide (JCPDS No. 31-657) was found ta every sample of the material submitted for analysis. Tbis compound has the stoichiometre formula (V, where x represents a small deviation from ideality resulting from structural defects. It is bcKcved that the Fc in this structure could be replaced by Ni without changing the difTraction pattern, providing a means for the incorporation of all three deposited metals together in one compound. 

With HREM, vanadium deposits were found in a layered structure both in the surrounding of the active phase, causing active site poisoning, and as isolated vanadium sulfide clusters, likely causing active site generation. In our vanadium deposition experiments (up to 9 wt.% vanadium) no significant catalyst deactivation occurred, indicating that both effects are compensated. 

Figure 6 shows a typical view of the spent Mo/SiOj catalyst with the layered structure of vanadium sulfide. According to EDX, vanadium sulfide is present on silica. The copper peaks in the EDX spectrum are due to the grid which supports the catalyst powder in the HREM. 

Patronite is a sulfide of vanadium as associated with pyrite and a carbonaceous substance which contains much free Knifin. It varies widely in composition, but a typical analysis gives vanadium sulfide 35 per cent, iron pyrite 5 per cent, free sulfur 35 per cent, and silica 15 per cent, with small amounts of molybdenum, nickel, aluminium, calcium, etc. It is found in the Andos Mountains, especially in Peru. 

The class of layered transition metal dichalcogenides has been of great interest because of their varied electronic properties and chemical reactions. Most compounds of this class may be prepared by stoichiometric reactions of the elements above 500°. However, the highest vanadium sulfide that can be made in this manner is VjSg. An amorphous VS has been prepared by the metathetical reaction of LijS and VC. The method presented here allows preparation of polycrystalline VSj with the Cdiz structure. ... 

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