News - full story

THE activity of solid acid catalysts has been increased by 100 times after scientists discovered new production methods, thanks to nanoscale imaging.

Chemical engineers and materials scientists at Rice and Lehigh Universities in the US, led by Wu Zhou, used aberration-corrected scanning electron transmission microscopy to obtain detailed images of the nanoscale structure of tungstated zirconia, a solid acid catalyst used for light alkane (C₄–C₈) isomerisation.

Alongside STEM, the team used three optical spectroscopy techniques - Raman spectroscopy, ultraviolet-visible and infrared spectroscopy. Israel Wachs, a Lehigh chemical engineering professor, says that it was the combination of methods which allowed the scientists to obtain the molecular level insights necessary to determine the origin of the acidity of the tungstated zirconia.

Solid acid catalysts are preferable to liquid catalysts as they cannot be spilt and can be disposed of more easily. Various catalytic tungsten oxide species were supported on the zirconium substrate, including monomers, polymer-like chains and sub-nanometre clusters. As they were able to see individual supported atoms, the researchers could determine which of the species showed the greatest catalytic activity. All the samples with high activity contained 3D tungsten oxide clusters measuring 0.8­–1 nm in diameter.

To test this, the researchers deposited some of these clusters onto a tungstated zirconia catalyst which had previously shown low catalytic activity. When tested, the catalytic activity increased by two orders of magnitude.

Michael Wong, from Rice University’s chemical and biomolecular engineering department, says: "By identifying the nano feature that is responsible for the desired catalytic performance, we can then focus research efforts on rationally designing new ways to prepare catalytic materials with only that particular feature."

The research was published in Nature Chemistry (doi: 10.1038/nchem.433).