Spectroscopie d'absorption X operando et catalyse hétérogène supportée pour l'environnement et les énergies nouvelles – SAXO

1- Scientific context Catalytic processes are more and more demanding in terms of conversion and selectivity, due especially to environmental issues. Therefore, a deep understanding for perfect control of the properties of catalytic sites is required, particularly in heterogeneous supported catalysis in which both the formation and the behaviour of the active supported nanophases, often present as oxide or metal nanospecies have to be perfectly tuned. Among the techniques available to characterize these systems, the French community of catalysis has for long used X-ray Absorption Spectroscopy (XAS), benefiting for it of close contacts with researchers of the LURE synchrotron. The obvious interest of this technique is to permit a direct identification of the local order, thus informing on the atomic environments and electronic states of the elements involved in the catalytic processes. However, due to technical limitations in first generation synchrotrons such as LURE, XAS studies were, until recently, often performed in restricted conditions, mostly ex situ and with long acquisition times, prohibiting any follow up of the properties of the nanophases during their formation, transformation and during reaction. Nevertheless, such time resolved studies are nowadays possible on third generation synchrotrons, and the opening of SOLEIL at spring 2007 represents a real opportunity to create in France a "pole of excellence" for the study of the preparation and running of catalysts by operando XAS approaches. This is indeed widely wished by the French community of catalysis, as attested by the discussions and workshops that took place in the context of the "Carayss" network (Catalyse et Rayonnement Synchrotron à SOLEIL). This ANR project aims at actively contributing to the development of such an approach, by gathering the competences of researchers working in the fields of catalysis and of X-ray Absorption Spectroscopy and looking at a common scientific issue dedicated to the optimisation of heterogeneous supported catalytic systems. 2- Project description The project covers scientific and technical aspects. It will be conducted following complementary steps that will involve constant collaboration between partners. The purpose will be firstly to elaborate adapted reactors for the study of the samples in operando conditions; the coupling of techniques will be also developed. The catalytic systems to investigate have been chosen in the field of competence of the different partners for their importance in environmental issues and clean fuel production. Joint efforts of all the partners will allow the progressive set up of operando XAS studies. The evolution of the nanophases during their formation and during catalytic runs will be followed in real time and under representative experimental conditions. The XAS data will be correlated to complementary information registered simultaneously, i.e. the catalytic activity (conversion and selectivity through the monitoring of the products with gas chromatography) but also other physicochemical characterizations obtained by direct "on line" coupling of techniques such as UV-Vis and Raman spectroscopies, calorimetry, or mass spectrometry. The studies will aim at i) optimising the steps of preparation and activation of the catalysts to increase their performances and ii) better controlling the behaviour of nanophases depending on the reaction conditions (both at steady state and under transient conditions). Lastly, an effort will be devoted to theoretical work with the aim to i) get increasing knowledge in the interpretation of XAS spectra and ii) model the nanophases in a context of a constant dialog between experiments and theory. 3- Expected results Three levels of results are expected: - "pole of excellence" in operando XAS: this project should contribute to the development, at SOLEIL, of a high level scientific and technical facility for time resolved operando studies that should benefit, at long term, to the whole catalysis community, especially for France and Europe. - design of supported catalytic systems: this project should permit to describe and control, at the atomic scale, the key parameters of the formation and behaviour of nanophases active in heterogeneous supported catalysis, - applications in environmental and clean fuel issues: the understanding of the properties of supported nanophases will help for elaborating new efficient catalytic systems for the protection of environment and the use of new energies.