Chromite, 856 table

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 only commercial ore, chromite [1308-31-2], which is also called chromite ore, chrome ore, and chrome, has the ideal composition Fe0-Cr2 03, ie, 68 wt % Cr202, 32 wt % FeO, or ca 46 wt % chromium. Actually the Cr Fe ratio varies considerably and the ores are better represented as (Fe,Mg)0-(Cr,Fe,Al)203. Table 1 gives the classification of chromite ores. 

The conversion of glycerol (Table 1) is generally higher in the presence of Ni, however Cu decreases the transformation. To a first approximation these results are in contrast to the data of Chiu et al. [3] who found copper-chromite to be an optimal catalyst in similar process. 

Preparation of Potassium Chromate. (Perform one experiment on each table.) Melt a mixture of 1 g of potassium carbonate, 1 gof potassium hydroxide, and 2 g of potassium nitrate in an iron crucible by heating with the flame of a burner. While stirring the melt with an iron wire, introduce 1 g of finely comminuted chromite or -0.8 g of chromium oxide into the crucible. Roast the mixture for 5-10 minutes on a blowpipe. Treat the cooled melt with water. Filter the solution and evaporate it until a crystalline film appears. What is the composition of the formed crystals Why was potassium carbonate introduced into the reaction Write the equation of the reaction. 

Table 21—1 outlines typical methods for obtaining the metals from their most important ores. The preparation of the iron-chromium alloy by direct reduction of the ore chromite is also listed since this alloy may be, in turn, used to make the very useful chromium alloys, chrome steel,... 

Effects of Catalysts. It has been found that copper chromite, potassium dichromate, and magnesium oxide promote the deflagration of hydrazine perchlorate. Since none of these additives has any fuel content, they must be considered to be catalysts. The results of experiments with these additives are shown in Table IV. Experiments were performed both with pressed (p 1.9 grams/cc.) and tamped (p 1.1. grams/cc.) strands. 

The condensation of a, dicarbonyl compounds (49) with aj3-diamino compounds (50), which proceeds through the dihydropyrazine (51), has been much used for the synthesis of alkyl- and arylpyrazines (52). These reactions are usually carried out in methanol, ethanol, or ether in the presence of sodium or potassium hydroxide. The dihydropyrazines may be isolated, or oxidized directly to the pyrazine. Dehydrogenating agents that have been employed include oxygen in aqueous alkali (329), air in the presence of potassium hydroxide (330), sodium amylate in amyl alcohol (330a), alcoholic ferric chloride (24), and copper chromite catalyst at 300° (331) (see also Section 1). Pyrazines prepared by this method and modifications described below are listed in Table II.8 (2, 6, 24, 60, 80,195, 329-382) and some additional data are provided in Sections VI. 1 A, VlII.lA(l), and IX.4A(1). 

The dehydrogenation of piperazines to pyrazine was first achieved by Stoehr (32), who heated piperazine (87) or its hydrochloride with zinc dust or, better, zinc dust and lime to give a yield of approximately 10% pyrazine (88). Since that time a number of publications and patents has described the conversion of piperazines to pyrazines by heating at elevated temperatures with various catalysts usually containing copper chromite (464) but also with palladium-charcoal (465) and platinum on alkali-washed firebrick (466), and also with other reagents. Some of these preparations are summarized in Table II.11 (464-475). 

The certain reserves of chromite were estimated in 1975 to be 2.8 10 t, the probable reserves to be 5.4 10 t. Of the certain reserves 74% are in South Africa and 20% in Zimbabwe. In South Africa the reserves are so large that the mining companies have not bothered to determine them accurately. Exhau.stion of the reserves in the near future is not to be expected. Important extracting countries outside Southern Africa are (in alphabetical order) Albania, Brazil, Finland, the former States of the USSR, India, Iran, Madagascar, the Philippines and Turkey. Table 3.3-2 gives the chromite extraction figures for 1992. 

Table III. Surface Area of Copper Chromite—Nickel Aluminate Solid Solutions Heated in Air as a Function of Calcination Temperature...

Third, the findings for copper chromite supported on Zr02 were similar to those for Co304 on Zr02 (Table III). Addition of Cr203 to the Co304 increased the HC activity and decreased the CO activity after aging (Table V). 

It was reported in the literature and also demonstrated in this laboratory that both Co304 and copper chromite are poisoned by sulfur. This results from the accumulation of sulfate groups on the catalyst surface. The base metal sulfates and aluminum sulfate are very stable, and they decomposed to the oxide only at temperatures above 650°C (see Table IV and Figure 2). Above 650°C, activity was restored because of sulfate decomposition. When a base metal catalyst was subjected to high temperatures before being cooled down for a CVS test, it had good activity for a short period of time which was dependent on the sulfur content of the gasoline and the surface areas of the washcoat and base metal catalyst. 

The activity of the 4.5-in. honeycombs with copper chromite as the active catalyst, when mounted 4 in. from the exhaust flanges of a vehicle and when used with low sulfur fuel (144 ppm S), appears to be somewhat less than that of a Pt honeycomb (for which we would expect >90% CO conversion and >80% HC conversion in the tests of Table VII). 

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