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Encyclopedia > Raney nickel

Raney nickel is an amorphous solid composed of finely divided grains of a nickel/aluminium alloy. In organic synthesis Raney nickel is commonly used as a heterogeneous catalyst for hydrogenation reactions. An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... Organic synthesis is the construction of organic molecules via chemical processes. ... A catalyst (Greek: καταλύτης, catalytēs) is a substance that accelerates the rate (speed) of a chemical reaction without itself being transformed or consumed by the reaction (see also catalysis). ... Hydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. ...


Since Raney is a registered trademark of W. R. Grace and Company, only those products by the Grace Davison division are properly called Raney nickel. Alternatively, the more generic term skeletal catalyst is used to refer to catalysts that have physical and chemical properties similar to those of Raney nickel.

Contents


Properties

Preparation

Alloy Preparation

Alloys are prepared commercially by melting the active metal (nickel in this case) and aluminium in a crucible and quenching the resultant melt, which is then crushed into a fine powder. This powder may be screened for a specific particle size range depending on the application the catalyst may be required for. Funckarma is a musical group formed by the brothers Don & Roel Funcken, from the Hague, Netherlands. ...


Alloy composition is very important because the quenching process produces a number of different Ni/Al phases that have different leaching properties. This results in markedly different porosities and crystallite sizes in the end product. The most common starting alloy used in industry contains an equal amount per weight of nickel and aluminium, coincidentally the same ratio Murray Raney used in his discovery of Raney nickel.


Activation

The porous structure of the catalyst arises from the selective removal of aluminium from alloy particles using aqueous sodium hydroxide. The leaching reaction is given by: Sodium hydroxide (NaOH), also known as caustic soda or lye, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents. ...

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

The formation of sodium aluminate (NaAlO2) requires that high concentrations of excess sodium hydroxide are used in order to avoid the formation of aluminium hydroxide which precipitates as bayerite causing blocking of the pores and loss of surface area, thus reducing catalyst activity. Aluminium hydroxide, Al(OH)3, is the most stable form of aluminium in normal conditions. ... Gibbsite, Al(OH)3, is an important ore of aluminium and is one of three minerals that make up the rock bauxite. ...


The temperature used to leach the alloy has a marked effect on the surface properties of the catalyst. The surface areas of Raney nickel (and skeletal catalysts in general) decrease with increasing temperature of leaching due to structural rearrangements that may be considered analogous to sintering. Sintering is a method for making objects from powder, increasing the adhesion between particles as they are heated. ...


After leaching the catalyst can be washed with distilled water at ambient temperature, and can be stored under deareated distilled water to prevent oxidation.


History

Murray Raney graduated as a Mechanical Engineer from the University of Kentucky in 1905. In 1915 he joined the Lookout Oil and Refining Company in Tennessee and was responsible for the installation of electrolytic cells for the production of hydrogen which was used in the hydrogenation of vegetable oils. During that time the industry used a nickel catalyst prepared from nickel oxide. Believing that better catalysts could be produced, he formed his own research company in 1921. In 1924 a 50% nickel-silicon 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. A patent for this discovery was issued in December 1925. The University of Kentucky (also as UK or simply Kentucky) is a public, co-educational university located in Lexington, Kentucky. ... State nickname: Volunteer State Other U.S. States Capital Nashville Largest city Memphis Governor Phil Bredesen (D) Official languages English Area 109,247 km² (36th)  - Land 106,846 km²  - Water 2,400 km² (2. ... 1925 was a common year starting on Thursday (link will take you to calendar). ...


Subsequently Raney produced a 50% nickel-aluminium alloy following a procedure similar to the one used for the nickel-silicon catalyst. He found that the resulting catalyst was even more active and filed a patent application in 1926. It may be of interest to note that Raney's choice of an alloy with 50% nickel-silicon content was fortuitous and without any real scientific basis. However, this is the preferred alloy composition for production of Raney nickel catalysts currently in use. 1926 was a common year starting on Friday (link will take you to calendar). ...


Following the development of Raney nickel, other alloy systems were considered. Some of the most notable include copper, ruthenium and cobalt. Sometimes a small amount of a third metal may be added to the binary alloy to enhance the activity of the catalyst, and as such they are called promoters. Some common promoters are zinc, molybdenum and chromium. General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance copper, metallic Atomic mass 63. ... General Name, Symbol, Number ruthenium, Ru, 44 Chemical series transition metals Group, Period, Block 8, 5, d Appearance silvery white metallic Atomic mass 101. ... This article is on the periodic element. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ...


References

  1. US1628190 - Murray Raney's patent on his nickel-aluminium catalyst.

External Links

  • Grace Davison - Product page for Raney catalysts. Includes a history section.
  • US1563587 - US patent of Raney's original nickel-silicon catalyst.
  • Preparation of Raney-Nickel W-2: Organic Syntheses, Coll. Vol. 3, p.181; Vol. 21, p.15 Article
  • Preparation of Raney-Nickel W-6: Organic Syntheses, Coll. Vol. 3, p.176; Vol. 29, p.24 Article

 
 

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