and thermal stability of the catalyst. As a result, the catalyst is quite resistant to decomposition ("breaking down", commonly known as "aging"). This resistance allows Raney nickel to be stored and reused for an extended period; however, fresh preparations are usually preferred for laboratory use. For this reason, commercial Raney nickel is available in both "active" and "inactive" forms. Before storage, the catalyst can be washed with distilled water at ambient temperature to remove remaining sodium aluminate. 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. Properties Macroscopically, Raney nickel is a finely divided, grey powder. 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. These properties are a direct result of the activation process and contribute to a relatively high catalytic activity. The surface area is typically determined by a BET measurement using a gas that is preferentially adsorbed on metallic surfaces, such as hydrogen. Using this type of measurement, almost all the exposed area in a particle of the catalyst has been shown to have Ni on its surface. Since Ni is the active metal of the catalyst, a large Ni surface area implies a large surface is available for reactions to occur simultaneously, which is reflected in an increased catalyst activity. Commercially available Raney nickel has an average Ni surface area of 100 m2 per gram of catalyst. A high catalytic activity, coupled with the fact that hydrogen is absorbed within the pores of the catalyst during activation, makes Raney nickel a useful catalyst for many hydrogenation reactions. Its structural and thermal stability (i.e., it does not decompose at high temperatures) allows its use under a wide range of reaction conditions. Additionally, the solubility of Raney nickel is negligible in most common laboratory solvents, with the exception of mineral acids such as hydrochloric acid, and its relatively high density (about 6.5 g cm−3) also facilitates its separation from a liquid phase after a reaction is completed. Applications Raney nickel is used in a large number of industrial processes and in organic synthesis because of its stability and high catalytic activity at