Chemical industry helped by small invisible tube

Chemists at Utrecht University have developed a catalyst for fine chemistry. Tiny tubes of graphite are the carrier for this catalyst. PhD student Tijmen Ros successfully tested the catalyst with a standard reaction. Fellow researchers are now making the catalyst suitable for the production of cinnamon alcohol, an aromatic substance and flavouring.

According to the researchers from Utrecht, carbon nanofibres will replace active carbon as a carrier for catalysts. Carbon nanofibres are small tubes made from graphite. Several tubes together from a sponge-like material with a large internal surface. In the optimum case a gram of tubes has a surface area of 200 m2. The researchers fix the catalyst, for example the metal rhodium, to the surface. Many small metal particles can be placed on a large surface and that produces a good catalyst.

Tijmen Ros investigated how effective the catalyst was in the hydrogenation of cyclohexene. Hydrogenation is a widely used reaction in the chemical industry. An example of hydrogenation is the hardening of fat to make butter from vegetable or animal oils. Colourings, aromatic substances and flavourings are also made by means of hydrogenation. Cyclohexene is a simple molecule used by the researchers to test the catalyst.

The catalyst turned out to be so effective that the supply of new hydrogen and not the catalyst was the rate-limiting step in the hydrogenation process.

The researchers first of all tested the carbon nanofibres with pure metal particles and then with metal complexes. Fine chemistry often uses pure metal particles but would rather work with complexes, as these are better at steering the reaction. A complex bound to carbon nanofibres makes it possible to reuse the catalyst. Although the complex used by the chemists appeared to have lost its activity, the researchers expect to be able to make active complexes in the future.

In the meantime, the Utrecht research group is investigating the industrially important hydrogenation of cinnamon aldehyde into cinnamon alcohol, a substance which tastes and smells like cinnamon. Most large companies are waiting until the efficacy of carbon nanofibres as a carrier for catalysts has been proven. The researchers expect that this will be the case within ten years.