Making hydrogenation greener

Instead of relying on heavy metals as catalysts, researchers have discovered a way to use iron which will make the process of hydrogenation both more environmentally friendly and less expensive.

Researchers from McGill University, Riken and the Institute for Molecular Science have discovered a way to make the widely used chemical process of hydrogenation more environmentally friendly - and less expensive.

Hydrogenation is used in a wide range of industrial applications, from food products, such as margarine, to petrochemicals and pharmaceuticals. The process typically involves the use of heavy metals, such as palladium or platinum, to catalyse the chemical reaction. While these metals are very efficient catalysts, they are also non-renewable, costly and subject to sharp price fluctuations on international markets.

Because these metals are also toxic, even in small quantities, they also raise environmental and safety concerns. Pharmaceutical companies, for example, must use expensive purification methods to limit residual levels of these elements in pharmaceutical products. Iron, by contrast, is both naturally abundant and far less toxic than heavy metals.

Previous work by other researchers has shown that iron nanoparticles - tiny pieces of metallic iron - can be used to activate the hydrogenation reaction. Iron, however, has a well-known drawback: it oxidises in the presence of oxygen or water. When oxidised, iron nanoparticles stop acting as hydrogenation catalysts. This problem, which occurs with so much as trace quantities of water, has prevented iron nanoparticles from being used in industry.

In research published in the journal Green Chemistry, scientists report that they have found a way to overcome this limitation, making iron an active catalyst in water-ethanol mixtures containing up to 90% water.

The key to this new method is to produce the particles directly inside a polymer matrix, composed of amphiphilic polymers based on polystyrene and polyethylene glycol. The polymer acts as a wrapping film that protects the iron surface from rusting in the presence of water, while allowing the reactants to reach the water and react.

This innovation enabled the researchers to use iron nanoparticles as a catalyst in a flow system, raising the possibility that iron could be used to replace platinum-series metals for hydrogenation under industrial conditions.

“Our research is now focused on achieving a better understanding of how the polymers are protecting the surface of the iron from water, while at the same time allowing the iron to interact with the substrate,” says Audrey Moores, an assistant professor of chemistry at McGill and co-corresponding author of the paper.

Co-author of the paper Prof Yasuhiro Uozumi of Riken and the Institute for Molecular Science says, “The approach we have developed through this collaboration could lead to more sustainable industrial processes. This technique provides a system in which the reaction can happen over and over with the same small amount of a catalytic material, and it enables it to take place in almost pure water - the green solvent par excellence.”