How Gold Becomes Active

Photo: A pile of gold coins

The team used nano-particles of gold instead of bulk gold. The catalyst structure looks as if someone had pulverized a piece of gold and spread the tiny nano-sized pieces over an aluminum oxide support. The properties of the nano-particles are very different from those of bulk gold. Only when the gold atoms are confined to the size of just a few millionth of a millimetre they start showing the desired catalytic behaviour.

Scientists already knew that gold nano-particles react with this kind of setup and catalyses carbon monoxide with oxygen into carbon dioxide. What they did not know was how the oxygen is activated on the catalyst. In order to find that out, they set up a cell where they could carry out the reaction, and in situ perform an X-ray experiment with the ESRF beam.

The researchers first applied a flow of oxygen over the gold nano-particles and observed how the oxygen becomes chemically active when bound on the gold nano-particles using high-energy resolution X-ray absorption spectroscopy. While constantly monitoring the samples, they switched to a flow of toxic carbon monoxide and found that the oxygen bound to the gold reacted with the carbon monoxide to form carbon dioxide. Without the gold nano-particles, this reaction does not take place.

"We have been able to observe, for the first time, the steps and path of the reaction. The results followed almost perfectly our original hypotheses”, comments Jeroen A. van Bokhoven, the corresponding author of the study paper.

The possible applications of this research could involve pollution control such as air cleaning, or purification of hydrogen streams used for fuel cells. "Regarding the technique we used, the exceptionally high structural detail that can be obtained with it could be used to study other catalytic systems, with the aim of making them more stable and perform better", says van Bokhoven.; Source: European Synchrotron Radiation Facility