Metal chromites

When relatively small amounts of hydrogen are required, perhaps in remote locations such as weather stations, then small transportable generators can be used which can produce I-I7m h. During production a 1 1 molar mixture of methanol and water is vaporized and passed over a base-metal chromite" type catalyst at 4(X)°C where it is cracked into hydrogen and carbon monoxide subsequently steam reacts with the carbon monoxide to produce the dioxide and more hydrogen ... 

Chromium chromium metal chromite (mineral form) chromic acid hexavalent (chromate) compounds carbamate, phosphate, and triacetate forms lung, nasal passages 2.78... 

Premalatha, K., Raghavan, P.S., and Viswanathan, B. (2012) Liquid phase oxidation of benzyl alcohol with molecular oxygen catalyzed by metal chromites. Appl Catal A Gen.,... 

Lazier of Du Pont published many patents covering the preparation of metal chromites." These were formed by precipitation from a solution of zinc nitrate and chromic acid with ammonia at pH 6.8. The zinc ammine complex obtained was decomposed at about 400°C to give the mixed oxides. As Adkins noted, his copper chromite equivalent was extracted with dilute acetic acid solution to adjust the copper content. It is not clear whether the same treatment was ever used in producing methanol catalysts or even whether the zinc ammine intermediate was produced commercially. One problem with the Lazier preparation was the difficulty in controlling the exothermic decomposition of the ammine that could affect the catalyst activity. 

All the complexes decompose exothermically at 300°C to their respective green metal chromites (Table 6.8). The formation of chromites has been confirmed by TG weight loss (Figure 6.12). The decomposed products have also been characterized by their XRD patterns. 

The principal ore is chromite, which is found in Zimbabwe, Russia, Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Phillippines. The metal is usually produced by reducing the oxide with aluminum. 

The result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the thin layer of soHd electrolyte (yttria-stabilized 2irconia) and the interconnection (Mg-doped lanthanum chromite). 

Hydrolysis of primary amides cataly2ed by acids or bases is very slow. Even more difficult is the hydrolysis of substituted amides. The dehydration of amides which produces nitriles is of great commercial value (8). Amides can also be reduced to primary and secondary amines using copper chromite catalyst (9) or metallic hydrides (10). The generally unreactive nature of amides makes them attractive for many appHcations where harsh conditions exist, such as high temperature, pressure, and physical shear. 

Fig. 1. Simplified flow chart for the production of metallic chromium and chromium compounds from chromite.

Recommendations by the ACGIH are classified as threshold limit values (TLV) based on 8-h TWA. Chromium metal and alloys, Cr(II) compounds and Cr(III) compounds, including chromite ore, have a TLV of 0.5 mg/m Cr in air. Water-soluble Cr(VI) compounds have a TLV of 0.05 mg/m Cr. Certain water-insoluble Cr(VI) compounds, ie, the chromates of 2inc, barium, calcium, lead, strontium, sintered chromic acid, and processing chromite ores, also have a TLV of 0.05 mg/m as well as a human carcinogen designation (145). 

The anode material in SOF(7s is a cermet (rnetal/cerarnic composite material) of 30 to 40 percent nickel in zirconia, and the cathode is lanthanum rnanganite doped with calcium oxide or strontium oxide. Both of these materials are porous and mixed ionic/electronic conductors. The bipolar separator typically is doped lanthanum chromite, but a metal can be used in cells operating below 1073 K (1472°F). The bipolar plate materials are dense and electronically conductive. 

The relatively high cost and lack of domestic supply of noble metals has spurred considerable efforts toward the development of nonnoble metal catalysts for automobile exhaust control. A very large number of base metal oxides and mixtures of oxides have been considered, especially the transition metals, such as copper, chromium, nickel, manganese, cobalt vanadium, and iron. Particularly prominent are the copper chromites, which are mixtures of the oxides of copper and chromium, with various promoters added. These materials are active in the oxidation of CO and hydrocarbons, as well as in the reduction of NO in the presence of CO (55-59). Rare earth oxides, such as lanthanum cobaltate and lanthanum lead manganite with Perovskite structure, have been investigated for CO oxidation, but have not been tested and shown to be sufficiently active under realistic and demanding conditions (60-63). Hopcalities are out-... 

The concentration dependence of CO oxidation over Pt at (02) (CO) l differs from the concentration dependence of CO oxidation over copper chromite at (02)°-2(C0). This can be explained by the fact that after the departure of a C02 molecule, the reoxidation of platinum surfaces is slow but the reoxidation of base metal oxide surfaces is fast. On the other hand,... 

The kinetic activities of noble metals and of base metal oxides are complementary, so that a mixture of the two would perform better than each class of material alone. We have already observed in Fig. 16 that noble metals have superior activity at high temperatures but base metal oxides have superior activity at low temperatures. Since the CO oxidation kinetics is negative first order with respect to CO over platinum but first order with respect to CO over copper chromite, the rates must be faster over platinum at low CO concentration but the reverse is true at high CO concentrations, as shown in Fig. 19. 

Chromium, Cr, is a bright, lustrous, corrosion-resistant metal. Its name, which comes from the Greek word for color, was inspired by its colorful compounds. The metal is obtained from the mineral chromite, FeCr204, by reduction with carbon in an electric arc furnace ... 

Chromium compounds of high purity can be produced from chromite ore without reduction to the free metal. The first step is the roasting of chromite ore in the presence of sodium carbonate ... 

In order to have more infoimation on the nature of the oxygen species active in partial and total oxidation we investigated the interaction of the hydrocarbons with the pre-oxidized surfaces of oxides where different types of surface oxygen species are formed. In particular we investigated p-type semiconductors like chromia, chromites and cobalt oxide C03O4. Moreover, we studied n-type metal oxides like FezOs, metal ferrites and CuObased catalysts. 

Cuprous oxide is also reduced violently by electropositive metals as discovered in an accident which occurred with aluminium. With chromium (III) oxide the reaction enables one to make copper chromite, which is a very common catalyst. The activity of copper chromite is such that it frequently combusts at the end of the reaction. 

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