Researchers from McGill University, RIKEN (The Institute of Physical and Chemical Research, Wako, Japan) and the Institute for Molecular Science (Okazaki, Japan) have discovered a technique enabling the use of iron nanoparticles as a catalyst for the industrially important hydrogenation process, making it more environmentally friendly and less expensive.
Hydrogenation—which is used in a wide range of industrial applications, from food products, such as margarine, to petrochemicals, pharmaceuticals and biofuels—typically involves the use of heavy metals, such as palladium or platinum, to catalyze 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. Iron, by contrast, is both naturally abundant and far less toxic than heavy metals.
Previous work by other researchers has shown that iron nanoparticles can be used to activate the hydrogenation reaction. Iron, however, rusts in the presence of oxygen or water. When rusted, 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 a paper published in the RSC journal Green Chemistry, scientists from McGill, RIKEN, and the Institute for Molecular Science 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 (a compound possessing both hydrophilic (water-loving) and lipophilic (fat-loving) properties) 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.
Highly efficient catalytic hydrogenations are achieved by using amphiphilic polymer-stabilized Fe(0) nanoparticle (Fe NP) catalysts in ethanol or water in a flow reactor. Alkenes, alkynes, aromatic imines and aldehydes were hydrogenated nearly quantitatively in most cases. Aliphatic amines and aldehydes, ketone, ester, arene, nitro, and aryl halide functionalities are not affected, which provides an interesting chemoselectivity.
The Fe NPs used in this system are stabilized and protected by an amphiphilic polymer resin, providing a unique system that combines long-term stability and high activity. The NPs were characterized by TEM of microtomed resin, which established that iron remains in the zero-valent form despite exposure to water and oxygen. The amphiphilic resin-supported Fe(0) nanoparticles in water and in flow provide a novel, robust, cheap and environmentally benign catalyst system for chemoselective hydrogenations.—Hudson et al.
This innovation enabled the researchers to use iron nanoparticles as 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.—Audrey Moores, an assistant professor of chemistry at McGill and co-corresponding author
The results stem from an ongoing collaboration between McGill and RIKEN, one of Japan’s largest scientific research organizations, in the fields of nanotechnology and green chemistry. Lead author Reuben Hudson, a doctoral student at McGill, worked on the project at the RIKEN Center for Sustainable Resource Science and at the Institute for Molecular Science in Japan. Co-authors of the paper are Prof. Chao-Jun Li of McGill, Dr. Go Hamasaka and Dr. Takao Osako of the Institute for Molecular Science, Dr. Yoichi M.A. Yamada of Riken and Prof. Yasuhiro Uozumi of Riken and the Institute for Molecular Science.
Our aim is to develop iron-based catalysts not only for hydrogenation but also a variety of organic transformations that can be used in future industrial applications. If rare metal-based catalysts can be replaced by iron-based ones, then we can overcome our costly dependency on rare metals.—RIKEN researcher Dr. Yoichi M. A. Yamada, co-author
Funding for the research was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Foundation for Innovation (CFI), the Canada Research Chairs, the Fonds de recherche du Québec – Nature et technologies, the Riken-McGill Fund, the Japan Society for the Promotion of Science (JSPS), and the Japan Science and Technology Agency (JST).
- Reuben Hudson, Go Hamasaka, Takao Osako, Yoichi M. A. Yamada, Chao-Jun Li, Yasuhiro Uozumi and Audrey Moores (2013) Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow. Green Chemistry doi: 10.1039/C3GC40789F