Raney type nickel-cobalt catalyst

Paul (17) has described nickel catalysts of the Raney type which were prepared from alloys of nickel, aluminum and cobalt, or chromium, or molybdenum. The alloy contained 52% aluminum to 48% of the other two metals. 

Excellent yields (93-97%) of 1,6-hexanediamine were obtained in the hydrogenation of adiponitrile over Raney Co (eq. 7.24), Co-A1203 (Raney type), and Co-kieselguhr as catalysts with addition of ammonia.22 The yields decreased from 97.2 to 93.1% in the absence of ammonia and from 93 to 77% with nickel catalyst in place of cobalt catalyst. 

Raney copper is another Raney type catalyst that is prepared from a copper-aluminum alloy. This catalyst has been used infrequently but does show some reaction selectivity not possible with other catalysts. Of particular interest is its use for the selective hydrogenation of substituted dinitrobenzenes (Eqn. 11.6).2 This catalyst, as well as Raney cobalt, generally promotes fewer side reactions than does Raney nickel. 25... 

This type of catalyst is not limited to nickel other examples are Raney-cobalt, Raney-copper and Raney-ruthenium. When dry, these catalysts are pyrophoric upon contact with air. Usually they are stored under water, which enables their use without risk. The pyrophoric character is due to the fact that the metal is highly dispersed, so in contact with oxygen fast oxidation takes place. Moreover, the metal contains hydrogen atoms and this adds to the pyrophoric nature. Besides the combustion of the metal also ignition of organic vapours present in the atmosphere can occur. Before start of the reaction it is a standard procedure to replace the water by organic solvents but care should be taken to exclude oxygen. Often alcohol is used. The water is decanted and the wet catalyst is washed repeatedly with alcohol. After several washes with absolute alcohol the last traces of water are removed. 

A special type of catalyst which is typified by Raney Nickel is prepared by leaching out one component from a binary alloy leaving a skeletal structure of the desired catalyst. Raney Nickel itself is made by leaching out aluminium from an aluminium-nickel alloy with sodium hydroxide. Cobalt and iron catalysts have also been prepared in this manner. 

Millions of tons of benzene are hydrogenated each year to give cyclohexane, which is converted to nylon via adipic acid. Whereas this process has been carried out with heterogeneous Raney nickel catalysts until now, a homogeneous process using Ziegler-type catalysts is about to take over. Catalysts based on nickel and cobalt salts in combination with triethylaluminum hydrogenate benzene under relatively mild conditions (155 °C, 1 MPa). This process is called the IFP process (Institut Fran ais du Petrole) [97] (cf Section 2.3.1.4). 

In most cases reductive alkylation involving hydrogen and a catalyst is carried out in an autoclave. The catalysts usually used for hydrogenations of this type are Raney nickel (more rarely Raney cobalt) and platinum metals. The hydrogen pressure and the reaction temperature needed depend largely on the activity of the carbonyl compound and the catalyst, and generalization is impossible. With nickel catalysts, hydrogen pressures of the order of 20 to 150 atm and reaction temperatures between 40° and 150° are required, but there are as many cases where reaction takes place smoothly at room temperature with pressures of 1-3 atm. 

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