Aluminium tungstates

Studies related to alumina-supported tungsten oxide metathesis catalysts also continue.Unsupported alumina tungstate, Al2(W04)3, has metathesis activity between 100 and 200° C it has been proposed that this difficult-to-reduce compound is a reasonable precursor to the active metathesis sites for tungsten oxide supported on 7-alumina. However, a controversy exists as to the presence of Al2(W04)3 as a major component on the surface of these catalysts Raman spectra do not show bands that can be attributed to Al2(W04)3. Evidence reported in the literature for the formation of aluminium tungstate on the surface is not valid because of impurities in the reference compounds used. The conclusion that this compound is not a major surface component does not completely rule out the possibility that it is involved in the catalytic active phase,especially since the number of active sites is extremely small, e.g., 10 sites per gram of... 

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. 

The activity for skeletal isomerization exhibited by these tungsten catalysts is developed only under specific conditions of treatment and operation. The source of tungsten oxide and the method of support are not critical. The HT-alumina favoured in these tests had the advantage of good dispersion of WO and limited loss by reaction with the support to form aluminium tungstate. 

Elsewhere, in a series of Japanese patents, mixtures of resorcinol + sodium nitrate, glycerine + sodium nitrate, lithium hydroxide + tungstate, etc., have been claimed to be effective. An example of the use of inhibited cooling mixtures of low toxicity is provided by a patent which describes a mixture of silicate-I- polyphosphate -I- a saccharide, e.g. sucrose or fructose, as the inhibitor formulation in a propylene glycol -I- potassium-hydrogen-carbonate mixture used in aluminium cooler boxes for ice-cream. 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

Aluminium paratungstafe, Al. Oa.VWOg.OHjO, is obtained by precipitating a solution of ammonium para tungstate with an aluminium salt. ... 

The following complex tungstates containing aluminium have been described ... 

Digestion with caustic soda produces the soluble sodium tungstate, but it is not applicable to scheelite ores. There is also extracted with the tungsten more or less molybdenum, vanadium, arsenic, tin, aluminium, columbium, and tantalum. 

In addition to the above, preparation in w/o microemulsions of nanoparticles of various other types of compounds, viz. silica-coated iron oxide, Fe203-Ag nanocomposite, oxides of ytrium, erbium, neodymium, vanadium and cobalt, titanates of barium and lead, ferrites of barium, strontium, manganese, cobalt and zinc, oxide superconductors, aluminates, zirconium silicate, barium tungstate, phosphates of calcium, aluminium and zinc, carbonates of calcium and barium, sulphides of molybdenum and sodium, selenides of cadmium and silver etc. have been reported. Preparative sources and related elaboration can be found in [24]. 

Alternatively, nerolidol can be isomerised into farnesol, via a trisilylated tungstate (formally a metalla-Claisen rearrangement). The product is purified by distillation. [246] After its conversion into farnesyl chloride, this is treated with carbon dioxide and freshly precipitated barium, giving ( , )-homofarnesylic acid, which is finally reduced with lithium aluminium hydride. [247, 248]... 

Cobalt group Chromium aluminium cobalt oxide Cobalt aluminium oxide Cobalt arsenate Cobalt arsenic oxide hydrate Cobalt chromate Cobalt hexacyanoferrate(II) Cobalt iron oxide Cobalt magnesium oxide Cobalt tin oxide Cobalt tungstate Cobalt zinc oxide Cobalt(III) oxide Erythrite Cobalt black Cobalt blue Cobalt violet... 

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