Oxides of Cr, Mo

It has been known for some time that norbornene undergoes ring-opening metathesis polymerization in the presence of Ziegler-Natta catalysts,reduced oxides of Cr, Mo, and and hydrated halides of Ru, Os, and Ir, resulting in an unsaturated polymer, poly(l,3-cyclopentylenevinylene). Norbornene also undergoes cationic polymerization in the presence of C2H5AlCl2, and FRP in the presence... 

Oxides of Cr, Mo, and W are usually used for catalysts as mixed oxides with other oxides such as alumina and silica which are prepared by coprecipitation, impregnation, etc. They are seldom put to practical use as simple oxides. Principal reactions catalyzed by these oxides, unlike those observed for silica-alumina or zeolites, often involve redox-type reaction steps, and during these steps reaction intermediates having covalent carbon-metal bonds are formed. Examples of those reactions are dehydrogeneration, hydrogenation and skeletal isomerization of hydrocarbons, and polymerization of olefms, as well as metathesis of olefins and hydrodesulfurization. Therefore, acid-base properties of catalysts usually play secondary roles in catalysts. 

Much attention has been devoted in recent litraatuie to the phenomenon of interaction between oxides (refs. 1-3). The supported oxides in the form of three-dimensional crystallites whose properties are similar to bulk crystals, do not interact strongly with the support. However, when the oxide is dispersed in monolayer on the oxidic supports, the interacdon between them becomes strong and the properties of such monolayer of the oxide differ from those of bulk oxide. Growth of three dimensional crystallites occurs only after a substantial fraction of the surface is covered by the monolayer and this is often the case for the oxides of Cr, Mo, W, V, Re and Ni. Extensive studies have been devoted to these systems. For other systems, however, the slate of dispersion is complicated, depending on the nature of the support, the preparative method and the conditions used in such process. In this paper, we tried to prepare well-dispersed iron oxide supported on various supports by different methods and investigate the physico-chemical properties of these iron oxides. 

Griskin et reported that there is no apparent effect of steam pressure on the rate of oxidation of Cr-Ni steels at temperatures between 600°C and 650°C at 10.1-20.2 MPa. Similar observations for Cr-Mo and Cr-Mo-V steels between 500°C and 600°C have been made by Wiles" . She compared low-alloy steel samples exposed to 101 kPa steam with power plant components that had operated for up to 150000b in steam at 17.25 MPa and found no significant difference in the oxidation rates (Fig. 7.11). 

The cyanocarbonylchromates(O) [Cr(CO)5CN]- and cis-[CifCOMCN) ] -, which are formed by the oxidation of [Cr l,(CO)s]2-with aqueous solutions of KCN or with (CN)2 or ICN have been discussed earlier (55, 56). Further studies have shown that the reaction of metal carbonyls or their derivatives with solutions of KCN in liquid NH3 is a most advantageous method for the synthesis of new cyanocarbonyl metalates of transition metals, since, in liquid NH3, alkali cyanides are not subject to solvolysis, and also since the broad temperature range of -78 to +120°C may be employed. Thus, we have been able to obtain quantitative yields of the tricyano-tricarbonyl metalates (0)/ac-[M(CO)3(CN)3]3 (M = Cr, Mo, W) by direct reaction of the hexacarbonyls (21) ... 

Introduction.—A report has been published listing heats of reaction and formation for chromium oxides and halides and for some chromates. Inorganic pyro compounds, M (X207)j, have been reviewed with consideration of species with X = Cr. A review of X-ray diffraction studies of the molecular structure of a number of Cr, Mo, and W complexes and organometallic compounds has appeared. ... 

Binary oxide catalysts are of major industrial importance. Such compounds are combinations of the oxides of Fe, Co, Ni, Cu, and Zn with those of Cr, Mo, and W. 

RE enhancing the selective oxidation of Cr to form stronger Cr203 scales Perez et al. [64] studied the effect of Si, Mo, and Ce implantation in AISI 304 stainless steel to test their corrosion resistance. At high temperatures. Si was found to behave similarly to a RE metal. Mo has beneficial properties in halide environments. 

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