The Metal Nanocrystals / Nanoparticles
Why use nanocrystals and nanoparticals in efforts to more efficiently oxidize CO? Professor Fornasiero explains:
“The use of nanocrystals is a key point to understand the reactivity of an heterogeneous catalyst and therefore to increase its efficiency. The characteristics of the nanocrystals, such as the shape and the dimensions for instance, are very important; in particular, it is important they all have comparable diameters (uniform size distribution).
We made our nanocrystals by dissolving salts of each metal in solution and adding an appropriate organic molecule (surfactant) to control the particle size, following the long experience of C. B. Murray (one of the authors of the paper) in the field. The particles were then dispersed on the surface of the support and calcined at 300 oC, to eliminate completely the organic molecules.”
The Role of the Support
To better understand the role of the support and how this can affect the reaction, the researchers compared two different supports, aluminum oxide (Al2O3) and cerium oxide (CeO2).
“We saw that the support really made the difference; when the nanoparticles were deposited on CeO2 their activity was much higher. On both supports the nickel nanocrystals were much less active than the platinum and palladium ones; however, the reactivity on CeO2 was significantly higher showing a size dependence, being small metal nanocrystals more active than medium or large ones..
The different behavior can be explained considering a different reaction mechanism, due to the different nature of the two supports. On cerium oxide, the support itself contributes to the reaction, by supplying oxygen to the carbon monoxide adsorbed on the nanocrystals surface. This does not happen with Al2O3.”
Reducing Pollution: Important Results
Commenting on the results, Professor Fornasiero said:
“With this study it was possible to clearly understand the mechanism behind this reaction. In particular, we carefully controlled the characteristics of the nanocrystals during the synthesis. In this way we could understand which are the surface sites active for the reaction. In future work we hope to maximize the active site numbers and to have a system which is even more effective. This means that, to prepare a catalyst, we could use less metal. Considering their cost, this could really be an important achievement.
Moreover, this principle could also be applied to catalysts for other reactions, hence leading to the optimization of different catalysts.”
Different and better catalysts, reduced carbon monoxide pollution – significant results indeed.
Cargnello, M. et al. Control of Metal Nanocrystal Size Reveals Metal-Support Interface Role for Ceria Catalyst. (2013). Science. DOI:10.1126/science.1240148. Accessed July 18, 2013.
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