CATALYSTS play an essential role in the chemical industry. But when the catalyst is an expensive metal like palladium, platinum or rhodium it has to be reclaimed when the reaction is over, and this can be a complex and messy business. Now a neat trick is promising to make the process clean and effortless 鈥� and make reactions go even faster too.
For a reaction to work well, the chemicals have to be in intimate contact with the catalyst. If the reaction takes place in a liquid and the catalyst is a solid, like the precious metals that are often used, this means dividing the catalyst into the smallest possible particles. The snag then is that the particles are hard to decant or filter off after the reaction.
One trick chemists have tried is to anchor the catalyst to a magnetic particle, and then use a magnetic field to pull them out when the reaction is over. But the magnetic particles can interfere with catalytic activity, and the magnetic particles are often destroyed by the very reactions they are there to help catalyse.
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Now a group in the UK including Shik-Chi Edman Tsang鈥檚 team at the University of Reading, David Chadwick at Imperial College London and David Thompsett from the Johnson Matthey Technology Centre near Reading have an answer. Their idea, reported in Angewandte Chemie International Edition, (vol 43, p 5645) is to protect the magnetic particle from the reaction with an inert graphite layer, then deposit the catalyst on the surface of the graphite. This seals the magnetic core so it does not interfere with the reaction, and because the catalytic particles are only 20 nanometres across they are very effective at speeding up reactions.
In tests, the new magnetic catalyst doubled the speed of the important reaction in which nitrobenzene is converted into aniline, compared with Johnson Matthey鈥檚 standard catalyst. At the end of the reaction, applying a magnetic field for a few minutes caused the particles to clump, making them easy to recover.
鈥淭his looks like a major advance for catalysis technology and could have far-reaching consequences for the industry鈥�
David Cole-Hamilton, an expert in catalysis at the University St Andrews in Scotland, says: 鈥淭his looks like a major advance for catalysis technology and could have far-reaching consequences for the chemicals industry.鈥�
