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Significant advance in our understanding of catalytic mechanisms on a nanometric scale

October 2014

Work carried out by Catalysis and Analysis researchers at IFP Energies nouvelles (IFPEN), in partnership with teams from the CNRS - Institut Néel and the Joseph Fourier University in Grenoble, has led to some significant advances in our understanding of catalytic mechanisms on a nanometric scale. These advances open up new avenues for improving matter transformation processes in the context of the energy transition.
The results have led to a publication[1] in the prestigious journal Angewandte Chemie. The article will be published in one of the forthcoming issues of the journal, in the VIP (Very Important Paper) category.


Value of better characterization of metal nanoparticles to enhance catalyst performance

Thanks to their optical, magnetic and electron properties, supported metal nanoparticles play a central role in nanotechnologies with numerous applications in the field of ICTs (Information and Communication technologies), nanoelectronics and data storage, sensors (detection of molecules), and, of course, chemistry (catalysis). In the latter case, nanoparticles based on platinum alone or as an alloy (with tin, indium or rhenium) supported on a special alumina (γ-Al2O3) are widely used to produce catalysts in the fine chemistry and petrochemicals sectors – hydrogenation, reforming, biomass conversion processes - or for the treatment of vehicle exhaust gases.
Improving these processes - which is a major challenge for various components of the energy transition - mainly involves improving the reactivity and selectivity of the catalysts used. These catalytic characteristics are closely linked to the geometry and local electron density of the metal particles, properties that are particularly difficult to define by experiments alone, given the very small size of the aggregates studied (diameter of approximately 0.8 nm).
XANES spectroscopy (X-Ray Absorption Near Edge Structure), using a synchrotron radiation source, is one of the best tools for studying these systems, especially in situ, on an atomic scale. This is because XANES spectra are influenced by the local geometry and symmetry of the atom environment (in particular, the angles between bonds), the degree of oxidation, the bond types involved and the electron structure of the system. However, it is difficult to differentiate between and interpret all these factors. It is therefore impossible to accurately deduce the structure of the metal particles using this method alone.


A combined observation and modeling approach

It is against this background that a thesis research project is underway at IFPEN[2]. The originality of this work lies in the use of quantum simulations to extract as much information as possible from the in situ high-resolution XANES experiments performed on the FAME beamline of the ESRF synchrotron in Grenoble.
Pertinent structural models produced using quantum calculations of Pt/γ-Al2O3 catalytic reforming catalysts at different partial hydrogen pressures have thus been proposed. The spectral characteristics of each model could then be calculated and compared with experiments.
Ultimately, by combining experimentation with calculation, it was possible to identify the morphology of the nanoparticles, their hydrogen coverage ratio and the exact nature of the chemical bonds they form with the alumina substrate.

Comparison between observation and modeling gives access to the catalytic mechanisms on a nanometric scale.


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[1] A. Gorczyca, V. Moizan, C. Chizallet, O. Proux, W. Del Net, E. Lahera, J.-L. Hazemann, P. Raybaud, Y. Joly, Monitoring morphology and hydrogen coverage of nanometric Pt/γ-Al2O3 particles by in situ HERFD-XANES and quantum simulations, Angew. Chem. Int. Ed. 2014
>> DOI: 10.10010.1002/anie.201403585.

[2] Thesis by Agnès Gorczyca, directed by Yves Joly at the Institut Néel (Grenoble) and jointly supervised at IFPEN by Céline Chizallet, Pascal Raybaud (Catalysis and Separation Division ) and Virginie Moizan (Physics and Analysis Division)

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