Small metal clusters make for clever catalysts

A carbohydrate polymer called cross-linked cyclodextrin provides a highly effective support material for tiny metal atom clusters, greatly improving their ability to catalyse chemical reactions.

Researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia developed and demonstrated the potential of the cyclodextrin-metal nanoparticles for catalysing ‘hydrogenation’ reactions, which add hydrogen to a variety of nitroarene compounds.

The researchers report that the catalysts achieved “outstanding performance” under mild, low temperature conditions.

“The most significant achievement is the unmatched selectivity,” says group leader Klaus-Viktor Peinemann. This achieves hydrogenation of specific chemical groups in a molecule while leaving other groups untouched. The researchers are not aware of any commercial catalysts with this selectivity.

The key to the success seems to be the ability of the cyclodextrin to hold a few tens of atoms in distinct clusters less than one nanometre across. The cyclodextrin polymer network avoids the problem of larger metal aggregates forming, which has curtailed the efficacy of alternative approaches.

The cyclodextrin appears to act synergistically with the metal clusters, rather than just supporting them. In addition to being highly effective, it is also a relatively inexpensive material, adding an economic advantage to the chemical ones.

The researchers have already built effective clusters using palladium, silver, gold and rhodium metal atoms. They are now moving on to extend the range of chemical reactions that can be catalysed, while exploring wider possibilities.

“We would also like to study possible applications, such as sensors or in optics,” says lead author Tiefan Huang.

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