Tungsten mixed oxides

Guidelli, E.J., Guerra, E.M., Mulato, M. Ion sensing properties of vanadium/tungsten mixed oxides. Mat. Chem. Phys. 125, 833-837 (2011)... 

Giebeler, L., Kampe, R, Wirth, A., et al. (2006). Structural Changes of Vanadium-Molybdenum-Tungsten Mixed Oxide Catalysts during the Selective Oxidation of Acrolein to Acrylic Acid, J. Mol. Catal. A Chem., 259, pp. 309-318. 

In 1789 M. H. Klaproth examined pitchblende, thought at the time to be a mixed oxide ore of zinc, iron and tungsten, and showed that it contained a new element which he named uranium after the recendy discovered planet, Uranus. Then in 1828 J. J. Berzelius obtained an oxide, from a Norwegian ore now known as thorite he named this thoria after the Scandinavian god of war and, by reduction of its tetrachloride with potassium, isolated the metal thorium. The same method was subsequendy used in 1841 by B. Peligot to effect the first preparation of metallic uranium. 

Finally, a number of other mixed oxides that do not have the perovskite structure have also been examined. For example, niobium titanates with the rutile structure,tetragonal tungsten bronze... 

Table 10 Molybdates, tungstates, and mixed-oxide compounds of molybdenum-(vi) and tungsten (vi) with s-, p-, and d-block elements...

Reaction with amorphous silicon at 900°C, catalyzed by steam produces cadmium orthosilicate, Cd2Si04. The same product also is obtained by reaction with sdica. Finely divided oxide reacts with dimethyl sulfate forming cadmium sulfate. Cadmium oxide, upon rapid heating with oxides of many other metals, such as iron, molybdenum, tungsten, titanium, tantalum, niobium, antimony, and arsenic, forms mixed oxides. For example, rapid heating with ferric oxide at 750°C produces cadmium ferrite, CdFe204 ... 

It can be only mentioned here that isopoly and betercpoly anions also give rise to highly colored mixed oxidation state species the tungsten bronzes64 and the heteropoly blues.63... 

The selectivity of alcohol depends on the carbide preparation. A maximum in alcohol is achieved for the sample WC/Ti02 (T3) for which the preparation of the carbide combines reduction and carburization steps at moderate temperatures (respectively, 873 K and 1073 K). In this case, anionic vacancies stabilized by mixed oxides are formed, associated with carbon vacancies in mixed carbides resulting in a better interaction of carbidic and oxidic phases. On silica, ceria and zirconia, the extent of carburization is too high and the interaction of the carbide phase with the oxide support is suppressed giving larger isolated particles of tungsten carbide with low dispersion. 

Typically, 38 g. (0.1 mole) of dichromium tungsten(VI) oxide and 18.7 g. (0.3 mole) of oven-dried, reagent-grade, magnesium fluoride are mixed and placed in a platinum crucible fitted with a cover. 

Six homologs in the mixed tungsten-molybdenum oxide series B,J03,J 1 have... 

As particle sizes decrease, the sensitivity of the thermite mixture to impact and friction increases. The micron scale thermites are usually quite insensitive to impact and shock, but thermites on the nanoscale can be quite sensitive to both or one of the two depending on the metal oxide. This is exemplified in the work of Spitzer, where a tungsten(VI) oxide and aluminum thermite was prepared by mixing nano and micron aluminum with nano and micron W03. The results of this are presented in Table 13.2. 

Numerous trinuclear cluster compounds are formed by molybdenum, and to a lesser but significant extent by tungsten and niobium. Four principal types are known, and their structures are shown schematically in Fig. 16-22. In all of these the M—M bond orders are in the range % to 1. For molybdenum particularly, there are numerous mixed oxides in which the type of structure shown in Fig. 16-22(b) figures prominently. 

Alkali tungsten bronzes of the type M WOs, M = K, Rb, or Cs with 0.16 < x 0.3 may adopt the hexagonal tungsten bronze (HTB) stmcture in which the large Cs atoms reside in hexagonal tunnels formed by six WOe octahedra in 12-fold coordination. The limit of x, as determined by the stmcture is 1/3. The stmcture is of interest since these compounds display superconductivity with values between 1 and 7K. It is also found for several mixed oxides of Nb and Ta with large A cations. 

Surface Vanadate, Molybdate and Tungstate Species The pure and mixed oxides and the salts of vanadium, molybdenum and tungsten in their higher oxidation states are used widely as heterogeneous catalysts, for selective oxidation as well as for acid catalysis. Similarly, supported chromia and rhenium oxides find wide application in different catalytic processes. 

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