Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A close look at catalysis by gold

23.06.2006
In recent years, gold has received more and more attention as a catalyst. ETH researchers have determined a possible reaction mechanism in these highly active catalysts, of the activation of oxygen on gold nano-particles. These results were obtained by using state-of-the-art time-resolved and high energy-resolution fluorescence detected X-ray spectroscopy on catalysts under reaction conditions.

Catalysis by gold has received considerable attention in recent years. Particles of gold have been reported to be very active in various oxidation reactions. The particle size greatly influences the catalytic activity of gold particles and with decreasing particle size, the activity increases. Moreover, the type of support also affects the catalytic activity. One example of a reaction with gold catalysts is the CO oxidation in presence or absence of hydrogen, which is relevant for the use of hydrogen in fuel cells. Regarding the mechanism, one of the main questions is how oxygen is activated on the catalyst. Jeroen A. van Bokhoven of ETH Zurich's Institute for Chemical and Bio-Engineering and colleagues at the ESRF, Grenoble, and the University of Southampton have now identified a possible reaction mechanism for the oxidation of CO over the gold particles in supported gold catalysts. The research results have been published in "Angewandte Chemie".

How gold activates the oxygen

The researchers studied gold supported on the nonreducible support Al2O3 and observed a reaction channel that has partially oxidized gold as reaction intermediate. Charge transfer from a reduced gold particle to oxygen activates the oxygen molecule. The researchers propose that reduced gold in small particles has the unique ability to transfer electrons to oxygen. A small fraction of the surface atoms are oxidized and are essential for high catalytic activity for oxidation of CO. The thermodynamic redox behaviour of small gold particles is distinctly different from that of bulk gold, which is inert. The difference likely originates from the different electronic properties of the small gold particles, which contain a large fraction of coordinatively unsaturated atoms with corner and edge positions. The latter have more d-electrons, which are additionally shifted towards the Fermi-level, than atoms in bulk gold. The electronic changes in nano-particles lead to stronger metal-adsorbate bonding and higher reactivity. Exposure of the gold-activated oxygen to CO rapidly forms CO2 and with re-reduction to metallic gold completing the catalytic cycle. Kinetic analysis of the individual reaction steps indicates that reduction is much faster than the re-oxidation and the rate-limiting step is the activation of oxygen on the gold surface.

Valuable tool in determining the structures of catalysts

For their experiments Jeroen A. van Bokhoven and colleagues combined in-situ time-resolved and in-situ high energy-resolution fluorescence detected X-ray spectroscopy. This method is likely to become a valuable tool in determining the structures of catalysts under catalytically relevant conditions. Combining high energy-resolution data with time-resolution and the possibility of in-situ measurement in combination with mass spectrometry at synchrotrons make it a promising tool in determining the structures of catalytically active sites.

Further information
Jeroen A. van Bokhoven
Institute for Chemical and Bioengineering
Phone +41 44 63 25542
Fax +41 44 63 21162
j.a.vanbokhoven@chem.ethz.ch
Original paper
Van Bokhoven J.A. et al, Activation of Oxygen on Gold-Alumina Catalysts:
In-situ High Energy-Resolution Fluorescence and Time-resolved X-ray Spectroscopy, Angewandte Chemie, early view

Beatrice Huber | idw
Further information:
http://dx.doi.org/10.1002/anie.200601184
http://www.ethz.ch

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Supersensitive through quantum entanglement

28.06.2017 | Physics and Astronomy

X-ray photoelectron spectroscopy under real ambient pressure conditions

28.06.2017 | Physics and Astronomy

Mice provide insight into genetics of autism spectrum disorders

28.06.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>