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International audience; γ-Al2O3 has remarkable properties as a support, but it is very sensitive to water, either as a liquid or even as steam. These structural changes can be retarded by the presence of polyols. The mechanism of action of these additives is believed to lie in their chemisorption on the surface that would make γ-Al2O3 water-resistant. However little is known on which exposed facet(s) and what site(s) need to be particularly targeted for protection. The optimization of the structure of inhibitors is therefore a challenging task since the exact mechanism of the decomposition of γ-Al2O3 in liquid water remains unknown. We combine here experiments and theory to provide the atomistic mechanism for the early-stage decomposition of γ-Al2O3 in liquid water. Beyond its impact on the stability of this important support, the present achievement constitutes an unprecedented milestone in the understanding of solid/liquid interface transformation in term of methodology.Alumina samples containing particles with different shapes were exposed to a hydrothermal treatment in presence of various concentrations of polyol (sorbitol and xylitol). We determined the minimum surface coverage of polyol at which the decomposition of alumina gets inhibited, a quantity referred to as inhibiting coverage. Since this inhibiting coverage strongly correlates with the fractional area of the (110) facet of the alumina sample and only with this area, we concluded that the decomposition is initiated at the (110) facet .Then, performing ab initio metadynamics simulations, we probed the reactivity of this Al2O3(110)/water interface and identified specific aluminum tetrahedral centers that are particularly reactive with water. We showed that interfacial water molecules are involved in the mechanism, both as reactants for the hydration of aluminum and as intermediates for the proton reshuffling required by the decomposition mechanism. We managed to determine the barriers (all lower than 80kJ.mol-1) for the 6 successive addition/elimination steps in a single simulation. Furthermore, the effect of xylitol was rationalized: its adsorption locally rendered the surface more hydrophobic and pushes water molecules away from the Al sites identified as water-sensitive.

International audience; 2D AND FAST 3D IN SITU CALCINATION AND REDUCTION OF Pd NANOCATALYSTS SUPPORTED ON ALUMINA IN ENVIRONMENTAL TRANSMISSION ELECTRON MICROSCOPYThierry Epicier1, Siddardha Koneti1, Lucian Roiban1, Anne-Sophie Gay2, Priscilla Avenier21Université de Lyon, MATEIS, INSA de Lyon, UCB Lyon 1, UMR 5510 CNRS, 69621 Villeurbanne Cedex, France2IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, FranceEnvironmental Transmission Electron Microscopy (ETEM) has recently open the way to operando studies of nanomaterials down to the atomic resolution in temperature and under a gaseous atmosphere that may reproduce more or less its real environmental conditions of use for real applications [1]. This is especially relevant in the field of nanoparticles (NPs) used in heterogeneous catalysis. The present work concerns the dynamic evolution of Pd small NPs (1-3 nm in size) supported on delta-Al2O3 platelets during the catalysis preparation process. This system has important applications, for example in petrochemistry or environmental catalysis. The calcination and reduction steps are followed under O2 and H2 up to 500°C in a FEI TITAN-ETEM microscope operated at 300 kV. Nowadays attention is paid to the “identical location” approach in TEM [2], where the same Region of Interest (ROI) is studied ‘before’ and ‘after’ a solicitation (heat treatment, exposure to gas…) performed outside the microscope. Typical results will show that this strategy is implicit in ETEM: the same ROI is naturally tracked at any stage during its dynamic evolution. One of the main key features insuring the catalytic efficiency of NPs is their resistance to sintering and their ability to remain homogeneously distributed during the calcination and reduction processes. The first point has been quantified through size measurements at different stages of the preparation process. The second point requires evaluating the localization of NPs in 3D using Electron Tomography (ET). Conventional ET, either in the Scanning or Bright Field TEM modes, consists in acquiring 2D projections over a large angular range, a time-consuming process hardly compatible with an in situ approach. We have thus developed a fast ET procedure [3] allowing rapid acquisitions of tilt series for volume reconstruction in only 1 or 2 minutes and a few seconds in the best cases [4]. Therefore, several tomograms of the same area are recorded in situ without critical irradiation damage of the sample shortly exposed to the electron beam. Typical examples will be shown including statistical distribution parameters, such as the inter-NPs distances measured in different states [5]. [1] ‘Controlled Atmosphere Transmission Electron Microscopy’, ed. T.W. Hansen, J.B. Wagner, Springer, New York (2016) 332 p.[2] K.J.J. Mayrhofer et al., Chem. Comm. 10 (2008) 1144-1147.[3] L. Roiban et al., J. of Microscopy, 269 (2018) 117-126.[4] H. Banjak et al., Ultramicroscopy, 189 (2018) 109-123.[5] CLYM (www.clym.fr) is acknowledged for access to the ETEM which was financially supported by the CNRS, the Région Rhône-Alpes, the ‘GrandLyon’ and the French Ministry of Research and Higher Education. This work is supported by the French National Research Agency ANR (3DCLEAN project n°15-CE09-0009-01).

International audience; The understanding of water effects on solid acid catalysts is a key issue in developing efficient processesto produce olefins by bio-alcohols dehydration. In this work, the effects of water on TiO2/SiO2 catalysts forthe gas phase conversion of isobutanol into linear olefins have been unraveled, using for the first timein situ acidity measurements achieved with a flowing NH3 probe and water vapor containing gas mixturesat adsorption equilibrium in the temperature range of the reaction. Such compounds, preparedby grafting titania onto mesoporous silica, contain well-dispersed TiO2 amorphous clusters anchoredby TiAOASi linkages, leading to much higher catalytic activity than TiO2 and SiO2. They yielded onlydehydration products, among which 30% were linear butenes. Furthermore, their activity was significantlyimproved by addition of water into the feed, whatever the contact time. Acidity measurementsindicated that TiO2/SiO2 mixed oxides were mostly of Lewis type after activation at 450 C. However,in situ FTIR acidity measurements showed that addition of H2O to NH3/He gas mixture has no influenceon the number of Lewis sites, while weak Brønsted sites were formed on other sites. This formation, dueto a shift of equilibrium depending on both the temperature and the H2O partial pressure, corresponds tothe hydrolysis of TiAOASi bonds, generating OH acidic groups and enhancing catalytic activity underwater vapor. The novel type of acidity measurements used in this work appear powerful and can beapplied to other acidic heterogeneous catalysts.

Carbon materials with different pore texture have been prepared by evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels. These carbon xerogels have been characterised and used as copper catalyst supports in the Selective Catalytic Reduction of NO by NH3 at low temperature. Without metal, some activity is observed due to reaction between NO and NH3, but the NO conversion is strongly enhanced after copper introduction. High deNOx efficiency was obtained on these Cu/carbon xerogels at very low temperature and some pore texture effect was observed. However, special cares have to be taken to avoid carbon consumption and preserve its surface by keeping reaction temperature below 215oC.

International audience; By choosing appropriate liquid oxidizing treatment, the carbonaceous surface of an activated carbon (AC) can be functionalised with carboxylic groups in a broad range of content. These carboxylic groups are necessary functions, in order to disperse, perfectly, palladium cations through exchange reactions: H+/Pd2+ or H+/Pd(OH)+. Reduction in liquid phase of a 4 mass %Pd/AC whose carbonaceous surface was previously oxidized by NaOCl leads to palladium particles with a particle size of 1.5 nm which are much smaller than Pd particles obtained from a 4 mass % Pd/AC whose carbon surface was not oxidized. The well dispersed catalyst was tested in hydrogenation of cinnamaldehyde and exhibits quite a high hydrogenation efficiency as compared to activities reported in the literature.