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Cooperative interaction between nanoparticles

One of the main motivations for the current intense interest in nanostructured materials is that the properties of very small solid objects may be different from those of bulk material, for instance due to quantum size effects, or the large surface to volume ratio. Much nanoscience is devoted to understanding the origin of these new properties, and how they can be exploited. Catalysts are an important class of nanomaterials, and are used to clean up automobile exhaust gas, carry out industrial reactions in the energy and chemical synthesis sectors (such as oxidation and water gas shift), and for a host of other applications. A particularly effective catalyst is platinum dispersed on cerium oxide, and the present work describes how insight has been gained into the reasons why this catalyst is so efficient.
This was shown by a group of researchers in an international collaboration led by Jörg Libuda (Universität Erlangen-Nürnberg, Germany) and Konstantin Neyman (ICREA / Universitat de Barcelona, Spain) and involving groups in Sofia, Prague and at Sincrotrone Trieste. The results of the project (supported by the Erlangen Center for Excellence in Advanced Materials Engineering) have been published in the journal Nature Materials 10, 310, (2011). The material studied here, platinum dispersed on cerium oxide nanoparticles, is extremely complex, so that is has been extraordinarily difficult to obtain insights into the way it works as an oxidation catalyst. For this reason, most practical catalysts are optimised empirically by trial and error, rather than by design on the basis of known principles.

The international research team has managed to make systems which model these catalysts accurately and has carried out modern quantum mechanical theoretical calculations. Together, theory and experiment offer the possibility of obtaining a detailed insight into these complex materials. It was found that it is exactly the nano structure which created the new properties of the material: the catalysts consist of oxide and metal particles of only a few nanometers in size, but they must be in close contact. The special chemical activity then comes about by cooperation between the different components.

Figure 1: Cerium oxide in the form of nanoparticles, unlike extended surface terraces, provides oxygen atoms that are mobile enough to catalytically activate platinum supported on them.

Only when they exist with the special form of nanoparticles can the highly reactive oxygen species be exchanged and open up new reaction paths, Figure 1. A catalyst made of all oxide or all metal does not work; poorer performance is obtained from nanoparticles of platinum on bulk cerium oxide or nanoparticles of oxide on bulk platinum.
The calculations found the optimised structures of Pt-CeO2 nanoparticles, see fig. 2, and the experiment provided spectroscopic data which benchmarked the calculations.

Figure 2: The most stable structure of Pt8 cluster adsorbed on the Ce21O42 nanoparticle. The blue circle shows the Ce3+ position.

This research was conducted by the following team:

  • Yaroslava Lykhach, Thorsten Staudt, Jörg Libuda, Universität Erlangen-Nürnberg, Germany
  • Annapaola Migani, Albert Bruix, Francesc Illas, Konstantin M. Neyman, ICREA / Universitat de Barcelona, Spain
  • Georgi N. Vayssilov, Galina P. Petrova, University of Sofia, Sofia, Bulgaria
  • Sofia Nataliya Tsud, Vladimir Matolin, Charles University, Praga, Czech Republic
  • Tomas Skála, Kevin C. Prince, Sincrotrone Trieste, Italy

Reference

G. N. Vayssilov, Y. Lykhach, A. Migani, T. Staudt, G. P. Petrova, N. Tsud, T. Skála, A. Bruix, F. Illas, K. C. Prince, V. Matolin, K. M. Neyman and J. Libuda “Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles”, Nature Materials 10, 310 (2011), doi:10.1038/NMAT2976.)

Last Updated on Wednesday, 16 May 2012 12:59