Oxidation of tungsten

Isopropyl Alcohol. Propylene may be easily hydrolyzed to isopropyl alcohol. Eady commercial processes involved the use of sulfuric acid in an indirect process (100). The disadvantage was the need to reconcentrate the sulfuric acid after hydrolysis. Direct catalytic hydration of propylene to 2-propanol followed commercialization of the sulfuric acid process and eliniinated the need for acid reconcentration, thus reducing corrosion problems, energy use, and air pollution by SO2 and organic sulfur compounds. Gas-phase hydration takes place over supported oxides of tungsten at 540 K and 25... 

Fig. 1.89 Oxidation of magnesium at 500°C illustrating the increase in rate to the constant value (Type 1) (after Gregg and Jepson ) and the oxidation of tungsten at 700°C (after Webb, Norton and Wagner ) illustrating the decrease in rate to the constant value (Type 2)...

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

Oxidation of tungsten with water and reduction of tungsten oxides with hydrogen are quite similar, with the high partial pressure of water or hydrogen driving the reaction in a particular direction. The oxidation reaction has been found to follow this sequence of reactions ... 

Non-stoichiometric compounds are found for the higher oxides of tungsten, molybdenum, and titanium—WOs-, MoOs-, and Ti02- f, respectively. The reaction of these systems to the presence of point defects is entirely different from what has been discussed previously. In fact, the point defects are eliminated by a process known as crystallographic shear (CS). 

Deuterium study of the mechanism of oxidation of tungsten rj1 -2,5-dihydrofur-3-yl compounds to rj1 -A3-butenolide derivatives... 

Sabatier and Maihle have stndied the catalytic action of various metallic oxides upon the vapours of certain organic compounds. They find that alcohols are oxidised to aldehydes by manganous oxide and that they are dehydrated by alumina, thoria or the blue oxide of tungsten, with the formation of olefines and ethers. Those changes are explained in the case of thoria by the following equations ... 

The reaction of K2W04 with IF5 at 120°C for 20 h has produced a material having a Raman spectrum consistent with the formation of W02F2 [302], High temperature oxidation of tungsten with a 6 1 02/F2 mixture in a Knudsen cell yielded W02F2 as the dominant product, which was detected by mass spectrometry [325],... 

Anti hydroxylation of an alkene is readily achieved with peroxycarboxylic adds. Add-catalyzed ring opening of the irutial produd, an oxirane (epoxide), forms the monoester of a 1,2-diol, hydrolysis of which affords the parent diol. Alternative reagents whi ate often used for anti hydroxylation of alkenes are hydrogen peroxide with oxides of tungsten > 4.2i gj. selenium, 444i and iodine-silver benzoate (Pr6vost reaction).. ... 

Total wine polyphenols are oxidised by the Folin-Ciocalteu reagent - composed of a mixture of phosphotungstic and phosphomolybdic acids which are reduced by the oxidation of the phenols, forming a mixture of blue oxides of tungsten and molybdenum. The blue coloration has an absorption maximum at approximately 750 nm, the intensity of which is proportional to the level of phenolic compounds present in the wine. The sequential analyser method is a direct automation of the manual method and results are expressed as a unit-less index. 

Three well-defined oxides of tungsten exist the brown, essentialh" basic, dioxide, WOj the yellow, essentially acidic, trioxide, WO3 and... 

A hydrosol of tungsten hydroxide is readily produced by the electrolysis of a 2 per cent, solution of sodium tungstate between a mercuiy cathode and a silver anode in a Hildebrand cell. The solution must not be allow ed to become acid, or blue compounds are produced. The hydrosols obtained in this way are clear and transj arent but brown in colour. The addition of potassium chloride causes coagulation, a black powder, resembling the lower oxides of tungsten, being formed. ... 

Tungstic Tungstate, or the blue oxide of tungsten, is described on p. 200. 

In the same group, the oxide of tungsten was observed to be a selective dehydration catalyst, irrespective of hydrogen or air pretreatment.Nevertheless, the octene distribution from octan-2-ol was affected by the pretreatment and as O " ions were removed, fra s-oct-2-ene became favoured and geometric factors are probably of importance. It was suggested that high cisitrans ratios may occur either when basic oxygen sites crowd closely around the catalytic site or when the metal ion has a lower co-ordination number. 

Oxidation [3.3]. The oxidation of tungsten depends strongly on temperature and on the oxygen partial pressure at elevated temperatures. A clean-looking tungsten surface between room temperature and 370 °C contains oxide. 

It was shown by ESCA investigations that the oxidation of tungsten by oxygen or air starts at room temperature. The oxide formed in oxygen as well as in dry or humid air is always tungsten trioxide. The thickness of the oxide layer increases slowly with increasing temperature up to 200 °C, but increases rapidly above 200 °C. Increase in humidity also accelerates the oxidation rate. 

Oxidation of Tungsten Metal Powder. Tungsten powder, of average grain size > 1 pm, reacts like bulk tungsten. Finer powder qualities, depending on grain size and preparation method, can be pyrophoric. 

By oxidation of tungsten powder (for stoichiometric WO3 the oxygen partial... 

The oxidation of tungsten in scrap material to the hexavalent state by heating in air or oxygen-eruiched air, because only hexavalent tungsten dissolves in an alkaline leach process. 

The active constituent of the catalyst is an oxide of tungsten prepared by partial reduction of WO - Unsupported WOj was found to have activity but better specific activity is obtained by depositing the oxide on a support. A number of grades of alumina and silica were tested. Gamma alumina was found to react with WOj at 400°C to a considerable extent to form aluminium tungstate. This was identified by XPS and tests on AljfWO ) showed it to be inactive as a catalyst for the isomerization reaction. 

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