Raney nickel 40-

CATALYST, RANEY NICKEL (With High Contents of Aluminum and Adsorbed Hydrogen) 

Submitted by Harry R. BimcA and Homer Adkins. Checked by Arthur C. Cope and Haroid R. Nace. 

Caution The Raney nickel catalysts described below cannot be used safely under all conditions of temperature, pressure, and ratio of catalyst to hydrogen acceptor which are employed with less active nickel catalysts. They are particularly elective for low-pressure hydrogenations. No difficulty has been encountered in their use at temperatures below 100°, or above 100° if the ratio of catalyst to possible hydrogen acceptor is 5% or less. Outside these limits their use sometimes has led to reactions proceeding with violence. In one case a hydrogenation proceeding at 125° and 5000 lb. showed a pressure rise to considerably more than 10,000 lb. before the reaction could he stopped or the pressure released. Several instances of sudden increases in pressure have been noted when 10-15 g. of catalyst was used with a similar amount of hydrogen acceptor in 

100 ml. of ethanol in the temperature range of 100-150° under 5000 Ih. of hydrogen in a homh of 270 jwf. void. Accordingly the catalysts should be used with caution for high-pressure hydrogenations. 

W-6 Raney nickel catalyst. In a 2-1. Erlenmeyer flask equipped with a thermometer and a stainless-steel stirrer are placed 600 ml. of distilled water and 160 g. of c.p. sodium hydroxide pellets. The solution is stirred rapidly and allowed to cool to 50° in an ice bath equipped with an ovei ow siphon. Then 125 g. of Raney nickel-aluminum alloy powder is added in small portions during a period of 25-30 minutes. The temperature is maintained at 50 2° by controlling the rate of addition of the alloy to the sodium hydroxide solution and the addition of ice to the cooling bath. When all the alloy has been added, the suspension is digested at 50 2° for 50 minutes with gentle stirring. It is usually necessary to remove the ice bath and replace it with a hot-water bath to keep the temperature constant. After this period of digestion the catalyst is washed with three 1-1. portions of distilled water by decantation (Note 1). 

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 consists of a nickel lattice with a large number of defects, formed during its production by dissolution of aluminum from aluminum-nickel alloys in 

The Raney nickel catalyst can usually be stabilized by 2 to 4 wt% titanium and additionally activated by a small percentage of molybdenum [95] or platinum [97]. Although Raney nickel has excellent hydrogen adsorption ability and relatively large surface area, some disadvantages have also been reported, such as high electrolyte diffusion resistance due to low pore volume and small pore size [98, 99], and insufficient conductivity [97]. One type of mitigation is to support Raney nickel on carbon blacks, which will decrease its electrolyte diffusion resistance and increase its electrical conductivity [97]. 

4 Typical Example Analysis - PtRu Aiioy as a CO-tolerant Catalyst for the HOR 

The oxidation reaction of adsorbed CO on most metal surfaces, including Pt and Ru, takes place by reacting with oxygen-containing species OHad through a Langmuir-Hinshelwood (L-H)-type reaction to form CO2 [2, 107]  

The eutectic and NiAl3 are very reactive toward hydroxide and easily lose the aluminum to give the skeletal nickel. Ni2Al3 reacts more slowly with base but the aluminum can be removed at 50°C and the material completely decomposed in boiling alkali.67,68 Catalysts prepared from the commercial alloy, pure NiAl3 and pure Ni2Al3 all have about the same activity when the preparation conditions are such that most of the aluminum is removed from each material.69 

The usual preparation procedure involves the addition of the alloy to a sodium hydroxide solution held at a specific temperature. This not only removes the aluminum but also generates an atmosphere of hydrogen that serves to activate 

A number of different types of classic Raney nickel catalysts with varying activities have been prepared by the addition of the commercially available alloy to sodium hydroxide solutions. These catalysts have been designated as Wl, W2, W3, W4, W5, W6, W7 and W8. The procedures utilized to prepare these catalysts differ in the amount of sodium hydroxide used, the temperature at which the alloy is added to the basic solution, the temperature and duration of alloy digestion after addition to the base and the method used to wash the catalyst free from the sodium aliuninate and the excess base. These differences are listed in Table 12.1. 

Wl Raney nickel is the least active of all of these catalysts with the possible exception of the W8 variety. This inactivity has been used to advantage, for instance, in the hydrogenation of 2,5-dihydroxy benzoic acid to cyclohexane carboxylic acid-3,5-dione (Eqn. 12.10). 2 jj,e use of the more active W7 catalyst for this reaction, resulted in considerable over-reduction of the product. 

The W2 3 variety is the most commonly used of all of the Raney nickel catalysts. The commercially available Raney nickel is generally regarded as a W2 catalyst. The commercial catalyst is supplied as an aqueous suspension. Before the catalyst can be used, however, the water must be replaced by ethanol or other suitable solvent. This is done by decanting the water, washing the residual catalyst several times with 95% ethanol, and decanting the solvent after each wash. Several washes, again by decantation, with absolute ethanol removes the last of the water and gives an ethanol suspension of the active 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 

Raney Ni Amount of NaOH USed Process of (w/w (mol/mol Alloy Alloy ) Al) Addition Digestion Washing Process Ref. 

W-l 1 + 0.25 1.35 In 2-3 h in a beaker surrounded by ice At 115-120°C for 4 h and 1 then for 3 h with addition of 2nd portion of NaOH By decantation 6 times washings on Buchner filter until neutral to litmus 3 times with 95% EtOH 47 

73 At 50°C in 25-30 min At 50°C for 50 min By decantations, followed by continuous washing until neutral to litmus 3 times with 95% EtOH and 3 times with absolute EtOH 49,51 

N1AI2 + 6NaOH — Ni + 2Na3AlC 3 + 3H2 Submitted by Ralph Mozingo. 

To prepare the catalyst under methylcyclohexane (Note 9), the catalyst, which has been prepared as above and washed free of alkali with water, but to which no alcohol has been added, is covered with 1 1. of methylcyclohexane which is distilled from an oil bath until all the water has been codistilled with the hydrocarbon, more of the methylcyclohexane being added from time to time so that the nickel always remains covered. When the catalyst is free from water it becomes freely suspended in the liquid. 

To prepare nickel under dioxane, dioxane (Note 10) is used in place of the methylcyclohexane above and the distillation is continued until the temperature of the vapor reaches xoi°. Caution. Do not use nickel in dioxane above 210° the dioxane may react almost explosively with hydrogen and Raney nickel above this temperature.) 

A Pyrex battery jar of about io-l. capacity is also suitable and is sufficiently large for the preparation of a batch of catalyst of two to three times the size given here. 

The stirrer should be provided with a motor which will not ignite the hydrogen. Either an induction motor or an air stirrer may be used. The stirrer blades may be made of glass, Monel, or stainless steel. 

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Raney nickel A special form of nickel prepared by treating an Al-Ni alloy with NaOH solution. The nickel is left in a spongy mass which is pyrophoric when dry. This form of nickel is a most powerful catalyst, especially for hydrogenations. 

P-Phenylethylamine is conveniently prepared by the hydrogenation under pressure of benzyl cyanide with Raney nickel catalyst (see Section VI,5) in the presence of either a saturated solution of dry ammonia in anhydrous methyl alcohol or of liquid ammonia the latter are added to suppress the formation of the secondary amine, di- P phenylethylamine ... 

Minute amounts of halide have a powerful poisoning effect upon the catalyst it is advisable to distil the benzyl cyanide from Raney nickel. 

In the practical applications of Raney nickel it is more convenient to measure the catalyst than to weigh it. The product, prepared as above, contains about 0-6 g. of the catalyst per millilitre of settled material a level teaspoonful is about 3 g. of nickel. 

An example of the application of the Raney nickel catalyst is given in Section IV,35 (p-phenylethylamine from benzyl cyanide). 

The catalyst, which may be regarded as complementary to Raney nickel (Section VI,5) is largely used for the hydrogenation of esters (esters of monobasic and of dibasic acids to alcohols and glycols respectively) ... 

Catalytic hydrogenation is mostly used to convert C—C triple bonds into C C double bonds and alkenes into alkanes or to replace allylic or benzylic hetero atoms by hydrogen (H. Kropf, 1980). Simple theory postulates cis- or syn-addition of hydrogen to the C—C triple or double bond with heterogeneous (R. L. Augustine, 1965, 1968, 1976 P. N. Rylander, 1979) and homogeneous (A. J. Birch, 1976) catalysts. Sulfur functions can be removed with reducing metals, e. g. with Raney nickel (G. R. Pettit, 1962 A). Heteroaromatic systems may be reduced with the aid of ruthenium on carbon. 

Nitro groups are efficiently reduced with hydrogen over Raney nickel catalyst (I. Fel-ner, 1967), with hydrides, or with metals. 

Single-bond cleavage with molecular hydrogen is termed hydrogenolysis. Palladium is the best catalyst for this purpose, platinum is not useful. Desulfurizations are most efficiently per-formed with Raney nickel (with or without hydrogen G.R. Pettit, 1962 A or with alkali metals in liquid ammonia or amines. The scheme below summarizes some classes of compounds most susceptible to hydrogenolysis. 

A mixture of 3-methoxy-2-nitro-P-pyrrolidinostyrene (lOg, 40 mmol) and Raney nickel (25 g) in methanol-THF (40 ml of each) was heated to 60"C and,... 

Gassman and co-workers developed a synthetic route from anilines to indoles and oxindoles which involves [2.3]-sigmatropic rearrangement of anilinosul-fonium ylides. These can be prepared from Ai-chloroanilines and ot-thiomcthyl-ketones or from an aniline and a chlorosulfonium salt[l]. The latter sequence is preferable for anilines with ER substituents. Rearrangement and cyclizalion occurs on treatment of the anilinosulfonium salts with EtjN. The initial cyclization product is a 3-(methylthio)indole and these can be desulfurized with Raney nickel. Use of 2-(methylthio)acetaldehyde generates 2,3-unsubstituled indoles after desulfurization[2]. Treatment of 3-methylthioindoles with tri-fiuoroacetic acid/thiosalieylie acid is a possible alternative to Raney nickel for desulfurization[3]. 

The Gassman synthesis has been a particularly useful method for the synthesis of oxindolcs[lb,8]. Use of methylthioacetate esters in the reactions leads to 3-(methylthio)oxindoles which can be desulfurized with Raney nickel. Desulfurization can also be done by reduction with zinc or tin[10,ll]. 

The above intermediate (8 g, 0.03 mol) in THF (80 ml) was stirred with Raney nickel (40g) for 2h and then carefully filtered. [CAUTION Raney nickel can ignite during filtrationf Cone. HCl (2 drops) was added to the filtrate and it was evaporated in vacuo. Recrystallization of the residue from 2-propanol gave the product (6,0 g) in 89% yield. 

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

The Raney nickel reduction of cyanothiazoles leads to the corresponding amino compounds (96). 

Adiponitrile undergoes the typical nitrile reactions, eg, hydrolysis to adipamide and adipic acid and alcoholysis to substituted amides and esters. The most important industrial reaction is the catalytic hydrogenation to hexamethylenediarnine. A variety of catalysts are used for this reduction including cobalt—nickel (46), cobalt manganese (47), cobalt boride (48), copper cobalt (49), and iron oxide (50), and Raney nickel (51). An extensive review on the hydrogenation of nitriles has been recendy pubUshed (10). 

Direct hydrohquefaction of biomass or wastes can be achieved by direct hydrogenation of wood chips on treatment at 10,132 kPa and 340 to 350°C with water and Raney nickel catalyst (45). The wood is completely converted to an oily Hquid, methane, and other hydrocarbon gases. Batch reaction times of 4 hours give oil yields of about 35 wt % of the feed the oil contains about 12 wt % oxygen and has a heating value of about 37.2 MJ /kg (16,000 Btu/lb). Distillation yields a significant fraction that boils in the same range as diesel fuel and is completely miscible with it. 

Catalytic methanation processes include (/) fixed or fluidized catalyst-bed reactors where temperature rise is controlled by heat exchange or by direct cooling using product gas recycle (2) through wall-cooled reactor where temperature is controlled by heat removal through the walls of catalyst-filled tubes (J) tube-wall reactors where a nickel—aluminum alloy is flame-sprayed and treated to form a Raney-nickel catalyst bonded to the reactor tube heat-exchange surface and (4) slurry or Hquid-phase (oil) methanation. 

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