Iron-copper-zinc-alkali catalyst

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. 

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. 

Manufacture of many important amino intermediates used for dyes and other purposes is usually by conversion or replacement of a substituent. For example, as already mentioned, in substituted nitro compounds, the nitro groups may be reduced with iron/hydrochloric acid, hydrogen and catalyst, or zinc in aqueous alkali. Partial reductions can be brought about with sodium sulfide. Amino groups may be introduced by replacing halogens in the aromatic ring. Another approach to amination is by attack on a substituted aromatic compound with ammonia or amines. Thus, for example, direct amination of p-chloronitrobenzene (15a) in the presence of a copper catalyst affords p-nitroaniline (15b) in almost quantitative yield l,4-dichloro-2-nitrobenzene (16) is converted in a similar way to 4-chloro-2-nitroaniline (17). Reactions of ammonia with carboxylic acids or anhydrides are carried out on an industrial scale. 

The best catalyst was found to consist of zinc oxide and copper (or copper oxide) with an admixture of compounds of chromium. The success of the operation depended upon (a) the absence of alkali, which would cause decomposition of the methanol and the production of higher alcohols and oily products, and (b) the complete elimination of all metals except copper, aluminum and tin from those parts of the apparatus which come in contact with the reacting gases. Contact of carbon monoxide with iron, nickel, or cobalt had to be avoided since they formed volatile carbonyls winch deposited metal, by decomposition, on the active catalyst surface and thereby acted as poisons to destroy activity. 

Pure iron(iii) oxide performs rather poorly as a WGS catalyst, due to rapid catalyst deactivation by sintering. Traditional iron catalysts typically consist of iron(iii) oxide (80-90% by mass), chromium(iii) oxide (8-10% by mass) and small amounts of other stabilisers and promoters such as copper(ii) oxide, aluminium oxide, alkali metals, zinc oxide and magnesium oxide. The small fraction of chromium(iii) oxide acts to prevent catalyst sintering, and also promotes the catalytic activity of iron. Catalyst deactivation is typically caused by poisons in the feedstock gases and by deposition of solids on the catalyst surface. 

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