Cobalt alkali-promoted

Wesner, D. A., Linden, G., and Bonzel, H. P. 1986. Alkali promotion on cobalt Surface analysis of the effects of potassium on carbon monoxide adsorption and Fischer-Tropsch reaction. Appl. Surf. Sci. 26 335-56. 

The carbon number distribution of Fischer-Tropsch products on both cobalt and iron catalysts can be clearly represented by superposition of two Anderson-Schulz-Flory (ASF) distributions characterized by two chain growth probabilities and the mass or molar fraction of products assigned to one of these distributions.7 10 In particular, this bimodal-type distribution is pronounced for iron catalysts promoted with alkali (e.g., K2C03). Comparing product distributions obtained on alkali-promoted and -unpromoted iron catalysts has shown that the distribution characterized by the lower growth probability a, is not affected by the promoter, while the growth probability a2 and the mass fraction f2 are considerably increased by addition of alkali.9 This is... 

Supported Rhodium Catalysts Alkali Promoters on Metal Surfaces Cobalt-Molybdenum Sulfide Hydrodesulfurization Catalysts Chromium Oxide Polymerization Catalysts... 

The elTiciency of cobalt and ruthenium catalysis is not very sensitive to the presence of promoters )21]. With cobalt, the addition of thorium and alkali promoters increases wax production and supports were incorporated to increase the active metal surface area. On the other hand, promoters and supports are essentia) for iron catalysts. 

Alkali-Promoted Precipitated Cobalt-Based Catalyst ... 

It is always mixtures of oxides that are reported to be active catalysts for higher alcohols, or metals with promoters alkalized iron and cobalt are examples of the latter type. The addition of alkali promoters, of which hydroxides, carbonates, and organic alkali compounds are the most frequent precursors, usually decreases the overall rate. However, it increases the... 

Technologically the evaluation of catalysts under realistic conditions is relevant. Thus in a detailed study of the effect of HgS in the syngas feed over alkali promoted cobalt-molybdenum sulphide catalysts, it is raised that the presence of hydrogen sulphide lowers the alcohol selectivity enhancing the hydrocarbon formation, even if the production of higher alcohols is enhanced at adequate HgS concentration levels. 

Iron catalyst for ammonia synthesis containing alumina, cobalt, and an alkali promoter and a method of producing the catalyst. J. R. Jennings (Imperial Chemical Industries Ltd). EP 174079 (1986) US 4668657 (1987). 

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. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

The hypothesis of formation of oxygenated compounds as intermediate products was rejected by Eidus on the basis of experiments on the conversion over cobalt of methyl and ethyl alcohols and formic acid which were found to form carbon monoxide and hydrogen in an intermediate step of the hydrocarbon synthesis (76). Methylene radicals are thought to be formed on nickel and cobalt catalysts (76) by hydrogenation of the unstable group CHOH formed by interaction of adsorbed carbon monoxide and hydrogen, while on iron catalysts methylene radicals are probably formed by hydrogenation of the carbide (78,81). Carbon dioxide was found to interact with the alkaline promoters on the surface of iron catalysts as little as 1 % potassium carbonate was found to occupy 30 to 40% of the active surface area. The alkali also promotes carbide formation and the synthesis reaction on iron (78). 

Electronic promoters, for example, the alkali oxides, enhance the specific activity ofiron-alnmina catalysts. However, they rednce the inner snrface or lower the thermal stability and the resistance to oxygen-containing catalyst poisons. Promoter oxides that are rednced to the metal during the activation process, and form an alloy with the iron, are a special group in which cobalt is an example that is in industrial use. Oxygen-containing compounds such as H2O, CO, CO2, and O2 only temporarily poison the iron catalysts in low concentrations. Sulfur, phosphorus, arsenic, and chlorine compounds poison the catalyst permanently. 

The use of Fe-Cr and especially Cu-Zn-Al WCS catalysts in present-day hydrogen plants is directly connected with moderate levels of sulfur-containing compounds in natural gas and naphtha that almost completely displaced coal as the feedstock. It is likely, however, that the incentives for the use of fossil fuels rich in sulfur can be revitalized in the future. If this scenario comes into play, sulfur-tolerant catalysts will be a must for WCS process. Such catalysts are already developed, but so far they have only found a limited use in some particular cases where feed gases with high concentrations of CO and sulfur compounds had to be converted. The best known of this type are cobalt-molybdenum compositions, which are usually supported over alumina and may be promoted with alkali... 

The catalysts which were found to lie effective in the formation of methane from hydrogen and cavlion monoxide with the greatest activity were composed of nickel, iron, cobalt, and molybdenum. The catalysts most active in methanol synthesis in general consists of the oxides or mixtures of the oxides of zinc, copper, or chromium. Iron promoted with alkali lias been found to be very active but not at all directive in the synthesis of aliphatic compounds from water-gas. With it only a very complex mixture results, which it is impossible to separate commercially into constituents. 

C. No promoters are known (except alkali) which are indispensable for the activities of iron catalysts. In contrast to cobalt, supports are not decisive for the results obtained. 

The catalyzed oxidation of ethanol to acetic accompanied by acetaldehyde oxidation may be accomplished by use of acetic acid solutions with a cobalt acetate catalyst. In an example, 252 g of acetaldehyde is fed to the catalyst solution for activation, and then 85.4 g of 100 per cent ethanol together with air is introduced. Conversion of ethanol is 94.2 per cent to acetic acid, 3.5 per cent unchanged, and 2.3 per cent to ethyl acetate. Temperatures below 145°C were used. Various other metal acetates have been patented for the above process, including the salts of alkali and alkaline-earth groups, salts of the platinum metals group, and salts of the chromium metals group. A solid palladium-on-alumina catalyst is active in promoting air oxidation of ethanol to acetic acid. ... 

Synthesis of Liquid Hydrocarbons by the Reduction of Carbon Mon-dxide. When carbon monoxide-hydrogen mixtures are passed over cobalt, iron, nickel, and some copper catalysts that are promoted with certain metallic oxides, particularly oxides of the alkali mietals, at temperatures in the range frmn about 200-300°C and pressures from about 1-25 atm, various hydrocarbons are formed according to the following type of reactions ... 

Catalyst re-assembling with iron means reaction of iron with carbon from CO-dissociation to create the FT-active carbide surface (generally enriched with alkali as the essential iron promoter). With cobalt, restructuring means segregation of the metal surface and thus sites disproportionation for such of chain growth and such for CH2- (monomer) formation. 

After generation of the synthesis gas, conversion to liquid hydrocarbons, waxes, alcohols, and ketones is achieved using an iron or a cobalt catalyst (Table 19.10) in fixed-bed or entrained-bed reactors. A variety of catalysts, among them magnetite (iron oxide), have been proposed and used for the Fischer-Tropsch synthesis (Kugler and Steffgen, 1979 Cooper et al., 1984 Hindermann et al., 1984 Mirodatos et al, 1984 Moser and Slocum, 1992). Magnesium oxide (MgO) is frequently added as a structural, or surface, promoter, and potassium oxide (or other alkali metal oxide) is often added as a chemical promoter (Dry and Ferreira, 1967,1968). 

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