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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).

Homogeneous metal complexes often display superior activity and selectivity in catalysis of chemical transformations. Heterogenization of these complexes by immobilization on solid supports has been used to facilitate recovery, but this is often associated with a decrease in catalytic performance. We here describe a novel approach of sizing and engineering the cavity structure of nanoporous materials as "nanoreactors" to assemble metal complexes by the "ship-in-the-bottle" synthesis to combine the best of homogeneous and heterogeneous catalysts. Catalysis occurred by free metal complexes in confined liquid in these nanoreactors, while the catalysts were recyclable as being heterogeneous at the macroscopic scale. Subnanometer tailoring of window sizes (0.5-3.7 nm) of the cavities (16-22 nm) allowed control over loading (6-70 mg-metal complex/g-support) and a high turnover frequency (40-600 h(-1)) for the hydrolytic kinetic resolution of 1,2-epoxyhexane. Most importantly, the 'heterogeneous homogeneous catalysts' showed enhanced thermal stability and were stable upon reuse approaching excellent turnover numbers of 100,000. We showed this that engineering and sizing of nanoreactors is a powerful approach to control performance of confined catalysts, and method is generally applicable in host guest catalysis.