Raney Nickel Catalyst

Raney's nickel catalyst is a solid heterogeneous catalyst consisting of fine grains of nickel-aluminium alloy with a porous structure, which was first used as a catalyst in the hydrogenation of vegetable oils by Murray Raney, an American engineer. The preparation process involves treating a nickel aluminium alloy with a concentrated sodium hydroxide solution, in which most of the aluminium will react with the sodium hydroxide and dissolve away, leaving many microscopic pores of varying sizes. In this way Raney nickel is superficially a fine grey powder, but microscopically each tiny particle in the powder is a three-dimensional porous structure. This porous structure gives it a greatly increased surface area, and the great surface area results in a high catalytic activity, which makes Raney nickel widely used as a heterogeneous catalyst in organic synthesis and industrial production of hydrogenation reactions.

Raney nickel is prepared using an alkali solution to remove the inactive metal atoms and form a porous skeleton and redistribute the active metal atoms on it, hence the image of Raney nickel as a skeletal nickel catalyst. In addition, depending on the type of active metal, similar catalysts include skeletal iron, skeletal copper, skeletal cobalt, etc. Unactivated Raney nickel (nickel aluminium alloy) has a silvery grey powder appearance and is somewhat flammable. After activation it turns into grey-black particles, which are unstable and can spontaneously combust in air due to the presence of active hydrogen, and are therefore usually stored in water or ethanol.

The classification of Raney Nickel catalysts is usually indicated by the symbol "W" and the numbers 1-7 to distinguish the specific type. The different types of Raney nickel differ in their preparation, activity and use. W-2 raney nickel is easy to prepare, moderately active and can meet the needs of most catalytic reactions. w-4~w-7 raney nickel are all highly active raney nickel, especially w-6 raney nickel, which has considerable catalytic activity but is more complex to prepare and is suitable for hydrogenation at low temperatures (below 100°C) and low pressures. Raney nickel catalysts can also be divided into non-chiral Raney nickel catalysts and chiral Raney nickel catalysts.