Raney nickel

During the quenching procedure, small amounts of a third metal, such as zinc or chromium, are added to enhance the activity of the resulting catalyst.

The surface area of Raney nickel (and related catalysts in general) tends to decrease with increasing leaching temperature.

[citation needed] During the activation process, Al is leached out of the NiAl3 and Ni2Al3 phases that are present in the alloy, while most of the Ni remains, in the form of NiAl.

[7] This resistance allows Raney nickel to be stored and reused for an extended period; however, fresh preparations are usually preferred for laboratory use.

Oxygen-free (degassed) water is preferred for storage to prevent oxidation of the catalyst, which would accelerate its aging process and result in reduced catalytic activity.

Microscopically, each particle of this powder is a three-dimensional mesh, with pores of irregular size and shape, the vast majority of which are created during the leaching process.

Raney nickel is notable for being thermally and structurally stable, as well as having a large Brunauer-Emmett-Teller (BET ) surface area.

Raney nickel is used in a large number of industrial processes and in organic synthesis because of its stability and high catalytic activity at room temperature.

For example, thioacetals will be reduced to hydrocarbons in the last step of the Mozingo reduction:[14][15] Thiols,[16] and sulfides[17] can be removed from aliphatic, aromatic, or heteroaromatic compounds.

Due to its large surface area and high volume of contained hydrogen gas, dry, activated Raney nickel is a pyrophoric material that requires handling under an inert atmosphere.

Even after reaction, residual Raney nickel contains significant amounts of hydrogen gas and may spontaneously ignite when exposed to air.

[27] Additionally, acute exposure to Raney nickel may cause irritation of the respiratory tract and nasal cavities, and causes pulmonary fibrosis if inhaled.

[28] Nickel is also rated as being a possible human carcinogen by the IARC (Group 2B, EU category 3) and teratogen, while the inhalation of fine aluminium oxide particles is associated with Shaver's disease.

In 1924 a 1:1 ratio Ni/Si alloy was produced, which after treatment with sodium hydroxide, was found to be five times more active than the best catalyst used in the hydrogenation of cottonseed oil.

[2][31] Following the development of Raney nickel, other alloy systems with aluminium were considered, of which the most notable include copper, ruthenium and cobalt.

Light-gray powder on a glass dish
Shiny metal can with hazard labels.
Raney nickel is pyrophoric and must be handled with care. This shipping container is filled with vermiculite to protect the sealed bottle inside.
A graph of temperature vs. weight percent of nickel in aluminium, showing stability regions of various AlNi, Al3Ni, AlNi3 and Al3Ni2 phases
Phase diagram of the Ni–Al system, showing relevant phases
SEM of Raney nickel catalyst in which crystals of 1-50 μm are seen.
A close-up of Raney nickel. Small cracks of approximately 1-100 nm width are seen within the crystals, causing the increased surface area.
Chemical reaction. Benzene converts to cyclohexane under the action of hydrogen and Raney nickel. Cyclohexane then oxidizes to adipic acid.
using Raney nickel catalyzes the hydrogenation benzene to cyclohexane for the production of nylon precursors.
Chemical reaction: Thioacetal breaks into ethane, nickel sulfide and a hydrocarbon under the action of hydrogen and Raney nickel.
Example of desulfurization of thioacetals using Raney nickel
Chemical reaction: Reduction of thiophene under the action of hydrogen, Raney nickel and methanol
Reduction of thiophene by Raney nickel
A square orange sticker with a flame picture.
Raney nickel is flammable.
A square orange sticker with a black cross on it.
Nickel metal is classified as "Harmful".
NFPA 704 four-colored diamond Health 1: Exposure would cause irritation but only minor residual injury. E.g. turpentine Flammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasoline Instability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calcium Special hazards (white): no code