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Minor faults in catalyst impose an obstacle to the chemical industry

04 January 2010 NWO (Netherlands Organization for Scientific Research)

One of the most important catalysts in the modern chemical industry is a troublemaker. The building blocks of zeolite ZSM-5 crystals, which are a sort of Swiss cheese with molecular size holes, are not joined together perfectly. The materials that have to pass through the crystals therefore often get stuck and don't react well. Dutch researcher Marianne Kox discovered the deviations in the miniscule but indispensable particles.

Nearly all medicines, fuels and other chemical products come into contact with catalysts at some stage of their ‘lives'. These help to convert one material, for instance crude oil, into another, such as petrol. Take a good look around and you can see the evidence of the hard work done by these catalyst particles everywhere. Marianne Kox studied one of the most important catalysts, zeolite ZSM-5 crystals. These particles look like pieces of Swiss cheese with miniscule channels through which the material that has to be converted must pass. But it seems some of the holes do not want to cooperate leading to differences within one individual catalyst particle.

‘Big Brother' of catalysis

Like a real ‘Big Brother', Marianne Kox spied on the zeolites with a combination of different micro-spectroscopic techniques. By doing so, she managed to study the zeolite particles in a space- and time-resolved manner, for example the interior of the catalyst in 3D. She discovered why some of the zeolite crystals were not behaving properly, and how their behaviour differed from one position in the crystal to another.

Depending on the shape of the crystals - for example a boat shape or even the shape of a coffin - the channels inside a zeolite crystal didn't seem to run properly, and they could get blocked. This was caused by the building blocks that make up the zeolite crystals not fitting together properly. As a result of this the catalyst did not function as well as it could. Thanks to the unique combination of techniques applied by Marianne Kox, individual catalyst particles and their working principles can be studied in more detail, making improvement of the catalyst possible.

Marianne Kox's research is part of the Vici project run by Bert Weckhuysen. The December 2009 issue of Nature Materials contained the article Morphology-dependent zeolite intergrowth structures leading to distinct internal and outer-surface molecular diffusion barriers, about this research, to which PhD researcher Lukasz Karwacki also contributed.

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