Molybdenum X

Molybdoenzymes other than the nitrogenases are usually termed oxomolybdoenzymes. This prefix relates to the nature of the catalysis effected, i.e. the net effect of the conversion (xanthine to uric acid, sulfite to sulfate, nitrate to nitrite, or aldehyde to carboxylate) corresponds to the transfer of one oxygen atom to or from the substrate. Furthermore, molybdenum X-edge EXAFS studies have established that this metal is coordinated to one or more terminal oxo groups in each enzyme studied by this technique.204... 

Contrary to the literature (ref. 4), molybdenum promotion did not bring to a rise in the specific activity of the catalyst in our reaction conditions. In fact there were decreases in the specific reaction rates. Adding high level of molybdenum (x = 0.4) made the rate drop considerably. However the activity of the molybdenum promoted catalysts was found proportional to their metallic surface area. Moreover, it was shown (ref. 13) that this metallic surface area was a direct function of the phase content in the alloy (Mo-doped Ni A13 with a low Mo content 0.2 at %). The agglomerates issued from P seem to be the only active phase in the hydrogenation of valeronitrile. This explains why all Mo-promoted catalysts had the same intrinsic activity but also why increasing the Mo promoter level did not affect the selectivity. 

Chatt J, Kubota M, Jeffery Leigh G, March FC, Mason R, Yarrow DJ (1974) A possible carbon dioxide complex of molybdenum and its rearrangement product di-p-carbonato-bis carbonyltris(dimethylphenylphosphine) molybdenum X-ray crystal stmcture. J Chem Soc... 

Fig. 9.9 Distribution of wavelengths of a molybdenum X-ray tube (adapted with permission from Cullity et al.. Elements of X-ray Diffraction, Prentice Hall, 2001) [12],...

Molybdenum. U.S. reserves and resources are about 3 and 13 x 10 t, respectively. World reserves and resources are about 6 and 23 x 10 t, respectively (108). The requirement for fertilizer is very small. 

Incandescent Lamps, Electronic Tubes, and Resistance Elements. Articles fashioned in any form from molybdenum and tungsten usually fall within the bounds of powder metallurgy. These metals normally are first produced as a powder. Both molybdenum and tungsten are used as targets in x-ray tubes, for stmctural shapes such as lead and grid wires in electron tubes, and as resistance elements in furnaces. 

The same properties that make molybdenum metal effective in high temperature furnace appHcations make it useful as support wires for tungsten filaments in incandescent light bulbs and as targets in x-ray tubes. 

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

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