Molybdates physical properties

While normal molybdates of alkali metals are aU water-soluble, those of other metals are only shghtly soluble in water. All these salts have high melting points. Physical properties of some orthomolybdates and their CAS numbers are presented below ... 

Like all the other transition elements, molybdenum is a metal, and it is widely used as an alloying element and as a metallic coating. Some of its physical properties are listed in Table 3.2. In chemical reactions it shows little tendency to form cations, which is usuaily a characteristic of metals. In fact its sait-forming properties resembie those of non-metals, in that it has the ability to form salts (molybdates, sulphomolybdates, etc) or other complex compounds with another metal and a non-metal such as oxygen, sulphur or a halogen. The chemistry of molybdenum is very... 

Fven though the literature on this topic has been mainly focussed on the structural and chemical-physical properties of Bi molybdates, and on the reachvity of its various polymorphs (the a, P and y structures), the industrial catalyst consists of several divalent and trivalent metal molybdates. Indeed, Bi is present in minor amounts in catalyst formulahons. The two classes of molybdate contribute differently to catalyhc performance (1) trivalent Bi/Fe/Cr molybdates, having the Schee-lite-type shucture, contain the catalytically active elements while (2) divalent Ni/Go/Fe/Mg molybdates, having the Wolframite-type structure, mainly enhance the catalyst re-oxidahon rate. 

The most selective catalysts for the oxidation of methanol to formaldehyde are molybdates. In many commercial processes, a mixture of ferric molybdate and molybdenum trioxide is used. Ferric molybdate has often been reported to be the major catalytically active phase with the excess molybdenum trioxide added to improve the physical properties of the catalyst and to maintain an adequate molybdenum concentration under reactor conditions(l,2). In some cases, a synergistic effect is claimed, with maximum catalytic activity for a mixture with an Fe/Mo ratio of l.T( 3j. A defect solid solution was also proposed( ). Aging of a commercial catalyst has been studied using a variety of analytical techniques(4) and it was concluded that deactivation can largely be account for by loss of molybdenum from the catalyst surface. 

Lead molybdate, PbMo04, has the scheelite structure typified by calcium tungstate. Discussions of the growth and physical properties of PbMo04 are included in papers on CaW04 (Ranon and Volterra, 1964). The ion in PbMo04 replaces the Pb ion, and some method of charge compensation must... 

For more than 30 years at Lomonosov Moscow State University, later at Karpov Institute of Physical Chemistry, and recently at the Swedish University of Agricultural Sciences, Uppsala (V. G. Kessler), the authors of this book have systematically studyiedthe synthesis and properties of homometallic alkoxides of Groups I-Vm of the Periodic Table, the bimetallic derivatives (alkox-oaluminates, -titanates, -zirconates, -niobates, -tantalates, -molybdates, -tung-... 

Bismuth Molybdate Catalysts. The Raman spectra of the bismuth molybdates, with Bi/Mo stoichiometric ratios between 0.67 and 14, have been examined using the FLS approach (see Section 3.2). " The bismuth molybdates fall into an unusual class of compounds, the ternary bismuth oxide systems Bi-M-0 (where M = Mo, W, V, Nb, and Ta) which exhibit a variety of interesting physical and chemical properties. Of commercial importance, the bismuth molybdates are heterogeneous catalysts for selective oxidations and ammoxidations (the Sohio process), for example, propylene ( 311 ) to acrolein (C3H4O) by oxidation or to acrylonitrile (C3H3N) by arrunoxidation. ... 

Several studies of the catalytic behavior of iron molybdates as a function of their physical and chemical properties show that surface acidity, related with Mo ions, is a necessary condition for the catalyst effectiveness for formaldehyde formation [8,9]. The oxidizing function is also necessary, though the activity is not necessarily determined by this function. In a recently study Sun-Kuo et al [6] demonstrated that catalytic behavior of iron... 

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