Bismuth tungstate

Bismuth Tungstates. A family of structures recently identified (23) to occur in the Bi/W/0 system is illustrated schematically in Figure 5. The individual members are made of interleaved 2 3 an< 3 ayer> t ie latter consisting of comer-sharing WO, octahedra. The resulting homologous series has a formula n 3n+3 ... 

Villa et al. [340] have shown that the bismuth tungstates are comparable with bismuth molybdates with respect to dehydrogenation catalysis, although activities and selectivities are somewhat lower. Although the phase structures are different, interesting catalysts are formed in a similar composition range Bi/W = 2/3 to 2/1. (Note that, in case of propene (amm)oxidation, tungstates are definitely inferior to molybdates.)... 

NOa can also undergo photoredox reactions on solid photocatalysts modified by coordination compounds, for example, on Ti02 modified by H2PtCl6 127) or on bismuth tungstate photocatalysts 128). 

Some exceptions have been reported, e.g., bismuth tungstate (Bi2WOg) shows a relatively high level of photocatalytic activity for oxidative decomposition of acetaldehyde in air (a) Amano, F. Nogami, K. Ohtani, B. J. Phys. Chem. C 2009, 113, 1536. (b) Amano, F. Nogami, K. Abe, R. Ohtani, B. J. Phys. Chem. C 2008, 112, 9320-9326. 

Normal Bismuth Tungstate, Big(W04)3, is dimorphous/ ciy stal-lising in (1) the monoclinic system,... 

Recently we have also studied the luminescence of a bismuth tungstate, viz. 

Exceptions to the use of the root name of the central atom are antimonate, bismuthate, carbonate, cobaltate, nickelate (or niccolate), nitrate, phosphate, tungstate (or wolframate), and zincate. 

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. 

Discussion. The procedure is based on the formation of yellow tetraiodo-antimonate(III) acid (HSbI4) when antimony(III) in sulphuric acid solution is treated with excess of potassium iodide solution. Spectrophotometric measurements may be made at 425 nm in the visible region or, more precisely, at 330 nm in the ultraviolet region. Appreciable amounts of bismuth, copper, lead, nickel, tin, tungstate, and molybdate interfere. 

Many heavy metals react with dithiol to give coloured precipitates, e.g. bismuth, iron(III), copper, nickel, cobalt, silver, mercury, lead, cadmium, arsenic, etc. molybdate and tungstate also react. Of the various interfering elements, only arsenic distils over with the tin when a mixture is distilled from a medium of concentrated sulphuric acid and concentrated hydrobromic acid in a current of carbon dioxide. If arsenic is present in quantities larger than that of the tin it should be removed. 

Bulk Mixed Oxide Catalysts. - Raman spectroscopy of bulk transition metal oxides encompasses a vast and well-established area of knowledge. Hie fundamental vibrational modes for many of the transitional metal oxide complexes have already been assigned and tabulated for systems in the solid and solution phases. Perhaps the most well-known and established of the metal oxides are the tungsten and molybdenum oxides because of their excellent Raman signals and applications in hydrotreating and oxidation catalysis. Examples of these two very important metal-oxide systems are presented below for bulk bismuth molybdate catalysts, in this section, and surface (two-dimensional) tungstate species in a later section. 

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