Nickel-aluminum alloy, activated

Raney Not a process, but a nickel catalyst widely used for hydrogenating organic compounds. It is made from a 50/50 nickel/aluminum alloy by leaching out the aluminum with concentrated aqueous sodium hydroxide. The product has a spongy texture and is highly active. Invented by M. Raney in 1926. The business was acquired by W. R. Grace in 1963. U.S. Patent 1,628,190. 

T-l Raney Nickel Catalyst. To prepare, proceed as follows in a one liter three necked flask containing 600 ml of a 10% sodium hydroxide solution, 40 g of Raney nickel aluminum alloy (50%) is added in small portions. During the addition the temp should be 90-95° and there should be good stirring (do not use a magnetic stirring device). After the addition is complete (25 to 30 min), stir for 1 hour more, and let the nickel settle to the bottom of the flask. Decant the solution off, wash with 5 times 200 ml of water, 5 times 50 ml of ethanol, in such a way to keep the nickel always covered with liquid. The catalyst must be stored under ethanol and refrigerated. It may he stored for three months and remain active. 

For maximum catalytic activity, the metal usually is prepared in a finely divided state. This is achieved for platinum and palladium by reducing the metal oxides with hydrogen prior to hydrogenation of the alkene. A specially active form of nickel ( Raney nickel ) is prepared from a nickel-aluminum alloy. Sodium hydroxide is added to the alloy to dissolve the aluminum. The nickel remains as a black powder which is pyrophoric (bums in air) if not kept moist ... 

To check the. general applicability of activation by alkali, Paty (44) extended the investigation to several functional groups. The addition of small amounts of sodium hydroxide considerably reduced the time for reduction of 2-methyl-2-butene, phenylacetonitrile, and anethole. Larger amounts of alkali, in the case of phenylacetonitrile and in the case of anethole, increased the time for complete hydrogenation. Paty considers that the activating effect is due to the action of sodium hydroxide on the residual aluminum or nickel-aluminum alloy in the catalyst. 

In 1925 and 1927 Raney patented a new method of preparation of an active catalyst from an alloy of a catalytic metal with a substance that may be dissolved by a solvent that will not attack the catalytic metal. First a nickel-silicon alloy was treated with aqueous sodium hydroxide to produce a pyrophoric nickel catalyst. Soon later, in 1927, the method was improved by treating a nickel-aluminum alloy with sodium hydroxide solution because the preparation and the pulverization of the aluminum alloy were easier. Some of most commonly used proportions of nickel and aluminum for the alloy are 50% Ni-50% Al, 42% Ni-58% Al, and 30% Ni-70% Al. The nickel catalyst thus prepared is highly active and now widely known as Raney Nickel, which is today probably the most commonly used nickel catalyst not only for laboratory uses but also for industrial applications.46... 

It has been claimed that a more active catalyst can be made by adding the sodium hydroxide solution to the nickel-aluminum alloy instead of vice versa But when this is done, care must be taken that the foam doesn t get out of control. Also, the alloy must be stirred into the solution so it can react. Other than that, the catalyst is prepared in exactly the same way. 

Raney nickel is produced when nickel-aluminum alloy is treated with sodium hydroxide that dissolves the aluminum, leaving many small pores. This newly activated porous structure has a very high surface area that is responsible for its catalytic behavior. (The surface area of activated aluminum is in the range of 300 m /g. The surface area of activated charcoal can be 500-2000 m /g.) Because it... 

Transition metal alloys, notably Raney nickel, have also been investigated extensively as catalysts because of their interesting electronic and chemical properties [94]. Raney nickel is a solid catalyst, composed of fine grains of a nickel-aluminum alloy, and has been used in many industrial processes. Its application in the fuel cell field has been focused on alkaline fuel cells (AFC) rather than PEM fuel cells, due to potential corrosion in PEM operation media. Raney nickel s unique catalytic activity for the HOR as a non-noble catalyst makes it worth inclusion in this chapter. 

Raney nickel is a highly active, finely divided form of the metal prepared by reaction of a nickel/aluminum alloy with concentrated sodium hydroxide, which removes most of the aluminum as Na[Al(OH)4], Although active for a very wide range of reductions, it has been particularly widely used for the reduction of nitriles, and the desulfurization of thioacetals, thioethers, and dithianes (see Section 19.3.3) (Figure 23.22). The careful disposal of the catalyst after use is very important once it has dried out, the metal is highly pyrophoric. 

Alloys are prepared commercially and in the laboratory by melting the active metal and aluminum in a crucible and quenching the resultant melt which is then crushed and screened to the particle size range required for a particular application. The alloy composition is very important as different phases leach quite differently leading to markedly different porosities and crystallite sizes of the active metal. Mondolfo [14] provides an excellent compilation of the binary and ternary phase diagrams for aluminum alloys including those used for the preparation of skeletal metal catalysts. Alloys of a number of compositions are available commercially for activation in the laboratory or plant. They include alloys of aluminum with nickel, copper, cobalt, chromium-nickel, molybdenum-nickel, cobalt-nickel, and iron-nickel. 

Raney cobalt, which is prepared from a commercially available cobalt aluminum alloy in the same way as is Raney nickel, has been shown to have catalytic activity but it is generally less active than Raney nickel and more sensitive to variations in the reaction procedure and catalyst aging than the nickel catalyst. 

Raney copper is prepared from the commercially available copper aluminum alloy. It does not have much to offer the synthetic chemist as only a few reactions are reported to be affected by this catalyst. Raney copper, as well as Raney cobalt, generally produces fewer side reactions than Raney nickel even though they usually require higher reaction temperatures for the same reaction. Raney copper is, however, quite usefiil for the selective hydrogenation of substituted dinitro benzenes (Eqn. 8.6) with its activity apparently increasing with continued reuse. Raney copper can also be used for the catalytic hydrolysis of hindered nitriles to the amides (Eqn. 12.13). "2... 

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