Cobalt oxide catalyst, ammonia oxidation

Bimetallic Co-Mo oxide specimens were prepared via co-impregnation of calculated amounts of cobalt nitrate and ammonia heptamolybdate on y-alumina to achieve a total metal loading of 20wt% with an equimolar Co Mo ratio. Nitridation of catalysts was carried in a fixed bed... 

Mossbauer spectroscopy is one of the techniques that is relatively little used in catalysis. Nevertheless, it has yielded very useful information on a number of important catalysts, such as the iron catalyst for Fischer-Tropsch and ammonia synthesis, and the cobalt-molybdenum catalyst for hydrodesulfurization reactions. The technique is limited to those elements that exhibit the Mossbauer effect. Iron, tin, iridium, ruthenium, antimony, platinum and gold are the ones relevant for catalysis. Through the Mossbauer effect in iron, one can also obtain information on the state of cobalt. Mossbauer spectroscopy provides valuable information on oxidation states, magnetic fields, lattice symmetry and lattice vibrations. Several books on Mossbauer spectroscopy [1-3] and reviews on the application of the technique on catalysts [4—8] are available. 

Reduction. Benzene can be reduced to cyclohexane [110-82-7], C5H12, or cycloolefins. At room temperature and ordinary pressure, benzene, either alone or in hydrocarbon solvents, is quantitatively reduced to cyclohexane with hydrogen and nickel or cobalt (14) catalysts. Catalytic vapor-phase hydrogenation of benzene is readily accomplished at about 200°C with nickel catalysts. Nickel or platinum catalysts are deactivated by the presence of sulfur-containing impurities in the benzene and these metals should only be used with thiophene-free benzene. Catalysts less active and less sensitive to sulfur, such as molybdenum oxide or sulfide, can be used when benzene is contaminated with sulfur-containing impurities. Benzene is reduced to 1,4-cydohexadiene [628-41-1], C6HS, with alkali metals in liquid ammonia solution in the presence of alcohols (15). 

Each c.c. of free space corresponds with 20 sq. cms. of catalyst surface. E. I. Orloff observed the oxidation of ammonia when mixed with air and passed over a heated copper gauze 4NH3-f-302 =2N2+6H20, with traces of nitrous and nitric acids—aniline, toluidine, and pyridine were oxidized in a similar way. W. W. Scott and W. D. Leech found that the conversion efficiency of cobalt oxide at 600°-800° is 79 3 per cent. This is augmented when about 3 per cent, of bismuth, or 10 to 12 per cent, of alumina, is used as... 

Cobalt oxide (C03O4) catalysts are being used in some nitric acid plants as an alternative to platinum-rhodium (Pt-Rh). They generate less N2O, cost less and have a longer campaign life than Pt-Rh gauzes. (A paper in 2000 reported a conversion rate of ammonia to nitrous oxide as low as 0.5% over cobalt oxide catalyst)222. 

However cobalt oxide does have some drawbacks. Lower ammonia conversion efficiencies have been reported - as low as 88% to 92% in a high pressure plant compared with a typical value between 94% and 95% for Pt-Rh gauzes. The optimum operating temperature is 70 to 80°C lower than for Pt-Rh gauzes, and this could result in difficulties with the steam balance in a revamped plant. Cobalt oxide catalysts also suffer from reversible deactivation due to the reduction ofCo304 to CoO in the upper parts of the catalyst bed222. 

Interestingly sulphidic compounds, having a cation coordination which is similar to that of the oxides, show large differences in their sensitivity with respect to basic molecules like NH3. Whereas the desulphurization activity of cobalt sulphide catalysts is readily poisoned by ammonia, nickel sulphide maintains its activity to a significant extent. This agrees with the observed weak interaction of the adsorbent with the doubly occupied dangling bond orbital of the Ni2+ ion. 

In general, the catalysts contain varying quantities of the oxides of aluminum, potassium, calcium, magnesium, and silicon as promoters. Patents recommend adding sodium [243], beryllium [244], vanadium [245], uranium [246], or platinum [247]. Reference [248] describes cesium-containing catalysts. Catalysts patented by Lummus [249] and Ammonia Casale [250] contain cerium as additional promoter. ICI [251] has developed a cobalt-containing catalyst, as has Grande Paroisse [252]. 

The cobalt oxide catalyst for oxidation of ammonia, worked out in our laboratory, has the form of granules of high mechanical strength, owing to which it may be applied both in stationary and in fluidized beds. The yields of ammonia oxidation to NO measured during laboratory and large laboratory studies of that catalyst exceeded 95%. Optimum temperature of ammonia oxidation process carried out on our catalyst (760-780 ) is lower than that needed for platinum-rhodium wire gauze currently appli in industrial reactors. 

Ammonia synthesis catalysts consisting of magnetite containing a small amount of cobalt oxide. (Societe Chimique de la Grande Paroisse). NL 7203559 (1972) US 3839229 (1974). 

The ICI cobalt catalyst, which is reported to contain 10-20% cobalt oxide, was developed for use at 80 bar synthesis pressure and maximum temperatures as low as 460°C. These conditions were significantly different from the usual single-stream ammonia plants which operated at 150 bar or higher and temperatures up to 500°C. 

For this reaction, charcoal is a catalyst if this is omitted and hydrogen peroxide is used as the oxidant, a red aquopentammino-cobalt(lll) chloride, [Co(NH3)jH20]Cl3, is formed and treatment of this with concentrated hydrochloric acid gives the red chloro-p0itatnmino-coba. t(lll) chloride, [Co(NH3)5Cl]Cl2. In these latter two compounds, one ammonia ligand is replaced by one water molecule or one chloride ion it is a peculiarity of cobalt that these replacements are so easy and the pure products so readily isolated. In the examples quoted, the complex cobalt(III) state is easily obtained by oxidation of cobalt(II) in presence of ammonia, since... 

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Oxidation catalysts are either metals that chemisorb oxygen readily, such as platinum or silver, or transition metal oxides that are able to give and take oxygen by reason of their having several possible oxidation states. Ethylene oxide is formed with silver, ammonia is oxidized with platinum, and silver or copper in the form of metal screens catalyze the oxidation of methanol to formaldehyde. Cobalt catalysis is used in the following oxidations butane to acetic acid and to butyl-hydroperoxide, cyclohexane to cyclohexylperoxide, acetaldehyde to acetic acid and toluene to benzoic acid. PdCh-CuCb is used for many liquid-phase oxidations and V9O5 combinations for many vapor-phase oxidations. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

Balthis and Bailar6 obtained tris (ethylenediamine) chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt (III) com plexes. Mori7 described the preparation of hexaamminechromium(III) salts from the oxidation of chromium (II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic.8,9 Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer,100 in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product.106 The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

Molybdenum In its pure form, without additions, it is the most efficient catalyst of all the easily obtainable and reducible substances, and it is less easily poisoned than iron. It catalyzes in another way than iron, insofar as it forms analytically easily detectable amounts of metal nitrides (about 9% nitrogen content) during its catalytic action, whereas iron does not form, under synthesis conditions, analytically detectable quantities of a nitride. In this respect, molybdenum resembles tungsten, manganese and uranium which all form nitrides during their operation, as ammonia catalysts. Molybdenum is clearly promoted by nickel, cobalt and iron, but not by oxides such as alumina. Alkali metals can act favorably on molybdenum, but oxides of the alkali metals are harmful. Efficiency, as pure molybdenum, 1.5%, promoted up to 4% ammonia. 

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