Chromium oxide, copper sulfides

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

Hydrogen sulfide is rapidly oxidised, and may ignite in contact with a range of metal oxides, including barium peroxide, chromium trioxide, copper oxide, lead dioxide, manganese dioxide, nickel oxide, silver(I) oxide, silver(II) oxide, sodium peroxide, and thallium(III) oxide. In the presence of air, contact with mixtures of calcium oxide or barium oxide with mercury oxide or nickel oxide may cause vivid incandescence or explosion. 

Although all of the above elements catalyze hydrogenation, only platinum, palladium, rhodium, ruthenium and nickel are currently used. In addition some other elements and compounds were found useful for catalytic hydrogenation copper (to a very limited extent), oxides of copper and zinc combined with chromium oxide, rhenium heptoxide, heptasulfide and heptaselen-ide, and sulfides of cobalt, molybdenum and tungsten. 

Certain oxides, first of all zinc oxide17, as well as copper chromite18 (a mixed copper-chromium oxide), are also active in the saturation of the C=C bond. Partial sulfur treatment under controlled conditions of metals or oxides can result in sulfided catalysts which exhibit specific activity and selectivity in hydrogenations19-21. 

Oxidants. Hydrogen sulfide ignites on contact with silver bromate,8 bromine pentafluoride,9 mercury(I) bromate,10 lead hypochlorite,11 copper chromate,12 fluorine,13 fuming nitric acid,14 solid sodium peroxide,15 and dry or moist lead oxide.5 16 Dichlorine oxide17 or chlorine trifluoride18 explodes on contact with hydrogen sulfide. Heated chromium trioxide incandesces in a stream of hydrogen sulfide. 

Iron-chromium oxide catalysts, reduced with hydrogen-containing in the conversion plants, permit reactions temperatures of 350 to 380°C (high temperature conversion), the carbon monoxide content in the reaction gas is thereby reduced to ca. 3 to 4% by volume. Since, these catalysts are sensitive to impurities, cobalt- and molybdenum-(sulfide)-containing catalysts are used for gas mixtures with high sulfur contents. With copper oxide/zinc oxide catalysts the reaction proceeds at 200 to 250°C (low temperature conversion) and carbon monoxide contents of below 0.3% by volume are attained. This catalyst, in contrast to the iron oxide/chromium oxide high temperature conversion catalyst, is, however, very sensitive to sulfur compounds, which must be present in concentrations of less than 0.1 ppm. 

Typical fillers wood flour, glass fiber, carbon fiber, mica, wollastonite, mineral wool, talc, magnesium hydroxide, graphite, molybdenum sulfide, carbon black, cashew shell particles, alumina, chromium oxide, brass and copper powder, iron particles, steel fiber, ceramic powder, rubber particles, aramid, wollastonite, cellulosic fiber, lignin... 

Catalytic reductions have been carried out under an extremely wide range of reaction conditions. Temperatures of 20 C to over 300 C have been described. Pressures from atmospheric to several thousand pounds have been used. Catal3rsts have included nickel, copper, cobalt, chromium, iron, tin, silver, platinum, palladium, rhodium, molybdenum, tungsten, titanium and many others. They have been used as free metals, in finely divided form for enhanced activity, or as compounds (such as oxides or sulfides). Catalysts have been used singly and in combination, also on carriers, such as alumina, magnesia, carbon, silica, pumice, clays, earths, barium sulfate, etc., or in unsupported form. Reactions have been carried out with organic solvents, without solvents, and in water dispersion. Finally, various additives, such as sodium acetate, sodium hydroxide, sulfuric acid, ammonia, carbon monoxide, and others, have been used for special purposes. It is obvious that conditions must be varied from case to case to obtain optimum economics, yield, and quality. 

Some of the inorganic pigments used are based on heavy metals (e.g., barium, cadmium, iron, lead, mercury/chromium oxides, titanium, zinc, complex inorganic pigments as mixtures of two or more metal oxides, and sulfides), or they can be metals themselves (e.g., aluminium, copper, gold), dispersed as powders into the plastic bulk. 

Chromium oxide (fej Copper pMhabcyanlne bte, DIatomaceous earth Magnesium oxide, Mke, Pigment violet 19 Sllke, Tak, Titanium dioxide. Zinc oxide. Zinc sulfide colorant, food-contact mbber articles for repeated use Zinc chromate... 

The most common minerals of high metric tonnage (iron, aluminum, copper, titanium, nickel, chromium, magnesium, zinc, etc.) are found in nature as oxides and sulfides and as a combination of both. Ores are sometimes a mixture of rich metal composition and poorer compositions called gangue. The gangue can be acidic or alkaline, and determines the type of flux used for pyrometallurgy. Since ores come in all levels of complexity, various methods of processing have been developed over the years. 

Cadmium sulfides and selenides group Tin sulfides group Tungsten group Berndtite Cassiterite Chromium tin oxide Cobalt tin oxide Copper tin oxide Herzenbergite Lead antimony tin oxide Lead tin oxide Lead tin silicon oxide Ottemannite Romarchite Tin chromate Tin(IV) oxide Tin(IV) sulfide Bronze colours-, Egyptian blue Lead tin yellow Mosaic gold Mosaic silver, Tin white... 

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