Tungsten sulphides

Other onion-like structures reported recently include those built of tungsten sulphide and other inorganic materials [26e]. 

C.J. Wright, D. Fraser, R.B. Moyes P.B. Wells (1981). Appl. Catal., 1, 49-58. The adsorption of hydrogen and hydrogen sulphide on tungsten sulphide— Isotherm and neutron scattering studies. 

Voorhoeve, R. J. H. and J. C. M. Stuiver, Kinetics of Hydrogenation on Supported and Bulk Nickel Tungsten Sulphide Catalysts, J. Catal 23 (1971)... 

Finally, one should note that the fullerene cage concept is not just confined to carbon. Studies of boron nitride indicate that it too can form nanotubes [11,12]. Furthermore, most interestingly, Tenne and coworkers have shown that molybdenum and tungsten sulphides - long known to form layered materials also produce fullerene-related giant quasi-crystals [13,14]. 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

Scheme 1. Tungsten catalysed cross-metathesis of allyl methyl sulphide with pent-2-ene and but-2-ene...

The successful cross-metathesis of allyl methyl sulphide with ris-pent-2-ene and czs-but-2-ene, catalysed by the tungsten alkylidene 5, was reported by Basset and co-workers in 1993 [20] (Scheme 1). 

The report by Basset and co-workers on the metathesis of sulphur-containing alkenes using a tungsten alkylidene complex, mentioned previously for the acyclic cross-metathesis reaction (see Sect. 2.2), also contained early examples of ring-opening cross-metathesis of functionalised alkenes [20]. Allyl methyl sulphide was reacted with norbornene in the presence of the tungsten catalyst 5, to yield the desired ring-opened diene 35 (Eq. 29). 

Thiosalts and Sulphides of Molybdenum and Tungsten. Pour 2-3 ml of an ammonium molybdate solution into one test tube and 2-3 ml of a sodium tungstate solution into another one. Add 2-3 drops of a 25 % ammonia solution to each solution and pass a stream of hydrogen sulphide through them from a Kipp gas generator. What compounds form Acidify the solutions with a 10% hydrochloric... 

Reduction of MoIybdenum(VI) and Tungsten VI) Compounds. Pour 3 ml of an ammonium molybdate solution into each of four test tubes, acidify with a 2 N hydrochloric acid solution, and heat up to boiling. Add solutions of sulphuric acid, hydrogen sulphide, and tin(Il) chloride to three of the tubes, respectively, and throw one or two small pieces of zinc into the last tube. Perform similar experiments using sodium tungstate as the initial reactant. Write the equations of the reactions. 

Instead of lixiviating with water, the pyrosulphate fusion is followed in a recent process 7 by extraction with tartaric acid solution the insoluble residue contains silica, tin, and lead, and the solution, after being saturated with hydrogen sulphide for the precipitation of copper, antimony, etc., contains the hydroxides of niobium and tantalum as well as tungsten, titanium, zirconium, rare earth metals, etc. 

Besides powdered metals, certain metallic compounds are sometimes used for the same purposes, e.g., stannic sulphide (mosaic gold), antimony sulphide (iron bronze) and various oxygenated compounds of tungsten (tungsten bronzes). 

E.s.r. spectra have also been presented for molybdenum(v) centres in other iso- and hetero-polymolybdate blues479 and a theoretical description of these types of systems has been given.480 Results of an investigation of the photochromism of amine molybdates are consistent with the formation of mixed isopolyanions containing molybdenum-(v) and -(vi) centres.481 The lilac colouration formed during sulphide separations of molybdenum and tungsten appears to be due to the formation of a unit in which six tungsten(vi) atoms surround a molybdenum(v) centre.482... 

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