Hydrogenation of unsaturated organic compounds & polar functional groups using nickel, palladium or platinum as a catalyst is a well-established process. Nickel-based catalysts are favorable for such processes, as compared to noble metals (Palladium, Platinum, Ruthenium) since they are economical and abundantly available. So far, the Raney Nickel catalyst, a nickel-aluminum alloy in NaOH solution, has proven to be best suited for industrial hydrogenation processes.

However, Raney catalysts have several drawbacks:

  • A large surface area makes them pyrophoric,
  • Powdered forms of the catalyst are unsuitable for use in fixed-bed reactors,
  • Side reactions may occur due to the presence of minor quantities of Al2O3,
  • Need for storage under water causes challenges in catalyst measurements, and
  • Long-term storage causes loss of activity.

As a result, there has always been a need for a stable, inexpensive, highly reactive and non-noble metal based Raney catalyst substitute.

Several research groups have been working towards developing an efficient Raney catalyst substitute. In 2014, a group of researchers from the Beijing University of Chemical Technology and the SINOPEC Beijing Research Institute of Chemical Industry had developed a polymer-supported Raney catalyst for fixed-bed reactors. So far, several important chemical reactions such as nitroarene hydrogenation, reduction of amines, oxidation of heterocyclic compound and synthesis of (Hetero)aromatic or aliphatic nitriles have been successfully catalyzed by these polymer-supported Raney catalysts.

A recent study (June 2018) published by researchers from the Leibniz – Institute for Catalysis. V. at the University of Rostock, Germany, states that an intermetallic nickel silicide catalyst, Ni-phen@SiO2-1000, is a safe and gentle Raney nickel catalyst substitute. Interestingly, this isn’t the first time when Ni-Si has been reported as a catalyst. Back in the 1920s, Raney himself had a patent (US1563587), wherein, a 1:1 nickel-silicon combination had been used as a catalyst for hydrogenation of unsaturated organic compounds. However, no further study was conducted on this by Raney.

The University of Rostock researchers prepared the Ni-phen@SiO2-1000 catalyst by the thermal reduction of SiO2 below 1000OC. The process (Figure 1) was carried out in the presence of nickel nanoparticles.

Figure 1: Formation of nickel silicide nanoparticles.
(Source: http://advances.sciencemag.org/content/4/6/eaat0761.full)

 Formation of nickel silicide nanoparticles

The result is a stable, easier to handle, highly reactive intermetallic catalyst, capable of hydrogenating a wide variety of unsaturated organic compounds (Figure 2).

Figure 2: Hydrogenation of benchmark substrates with nickel-supported catalysts
(Source: http://advances.sciencemag.org/content/4/6/eaat0761.full)

 Hydrogenation of benchmark substrates

 

The serendipitous discovery of these intermetallic nickel silicides may hold great value for the industrial synthesis of many chemical compounds.

 

Author: Rafay Anwer