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SSCI-VIDE+ATARI:MEME+FCA:EEH:CLH:LMA:TEP; International audience; Observing liquids in a Transmission Electron Microscope (TEM) has long been impossible owing to basic thermodynamic limitations due to the need for a high vacuum, typically 10-5 mbar or better, within the column of the instrument, making it impossible to maintain a liquid state at room temperature. With the development of dedicated sealed liquid cells mounted on specific specimen holders, Liquid Cell TEM (LCTEM) has become possible about a decade ago, opening a huge range of possible applications in the field of biology, crystal growth or electrochemistry [1]. In parallel, Environmental TEM (ETEM) was also developed [2]; here a partial pressure can be maintained in the pole-pieces gap where the tip of the sample holder, including the sample itself, is inserted, allowing to perform observations under gas without any sealing membranes as needed with the close-cell technology. Such an ‘open-cell’ approach was also developed in Scanning EM (ESEM, e.g. [3]). With these dedicated ETEM or ESEM configurations, observing liquid such as water layers is possible under a partial pressure of a few mbar if the temperature is cooled down close to the dew point in order to insure a thermodynamic equilibrium between the solid, gas and liquid states: for water, the liquid state can effectively been stabilized in a temperature and pressure range of typically 0 to 11°C and 6 to 15 mbar respectively [4], which are conditions easily accessible in ETEM and ESEM. While LCTEM in a close-cell permits to reach atmospheric pressure, thus allowing to observe water at room temperature, it has the drawback of its advantage: the presence of top and bottom sealing membranes makes it very difficult to perform water condensation from a humid atmosphere and to control water vapor states. Such experiments are possible in ‘open-cell’ ESEM [5] and ETEM [6] and enhance our understanding of the hygroscopic behavior of atmospheric aerosol particles that are known to act as cloud condensation nuclei [7]. Hygroscopic growth, deliquescence and efflorescence of model and real) atmospheric nanoparticles can be directly visualized by these techniques. The present contribution aims at establishing conditions under which aerosols can be adequately observed in a Titan ETEM (FEI/TFS). We use a Gatan liquid-nitrogen (LN2) cryo-holder to cool down the specimen around 0°C. We adjust the temperature by mixing LN2 with a controlled quantity of ethanol. For the purpose of this preliminary investigation, we use NaCl nanoparticles, obtained by vaporizing a salt solution onto a classical holey carbon TEM grid, as a model aerosols. Observations were performed at 300 kV under a humid atmosphere generated by pumping a small sealed water reservoir connected to one of the input lines of the ETEM, the pumping being insured by the molecular turbopumps of its vacuum system. The presence of water (vapor) was controlled by the residual gas analyzer equipping the microscope and by Electron Energy-Loss Spectroscopy (EELS). In a first step, and considering the high voltage at which experiments were performed, a control of the electron flux and dose was realized using different illumination settings in order to define safe imaging conditions avoiding noticeable irradiation damage of the nanocrystals (Fig. 1). Then, both water condensation and evaporation have been performed to follow the evolution of NaCl cubes (Fig. 2). Results will be discussed in terms of relationships between percentage of relative humidity and water uptake of the NaCl particles as a function of T and P [8]. References:[1] FM Ross (Ed.), Liquid Cell Electron Microscopy (Advances in Microscopy and Microanalysis), Cambridge University Press, Cambridge (2017), 524 p.[2] TW Hansen, J.B. Wagner (Ed.), Controlled Atmosphere TEM, Springer, New York, (2016), 332 p.[3] A Bogner et al. Micron, 38 (2007) 390. [4] DJ Stokes. Principles and Practice of Variable Pressure/Environmental Scanning Electron Microscopy (VP-ESEM), (2008), John Wiley & Sons Ltd., 221 p.[5] RC Hoffman et al. J. Aerosol Science, 35 7 (2004) 869. [6] ME Wise et al. Aerosol Science & Technology, 39:9 (2005) 849; C Cassidy et al. Plos One, 12 11 (2017) e0186899; BDA Levin et al. Microscopy and Microanal. (2020) 1.[7] U Lohmann et al. An Introduction to Clouds: From the Microscale to Climate, Cambridge University Press, Cambridge, UK (2016), 391 p.[8] The authors acknowledge the Consortium Lyon – St-Etienne de Microscopie (CLYM, www.clym.fr), the Centre Technologique des Microstructures (http://microscopies.univ-lyon1.fr/) for practical assistance and the French National Research Agency (ANR, www.anr.fr) for supporting project ANR-20-CE42-0008.

MICROSCOPIE+ATARI:CARE:ING+FCA:MAO:FRM:LMA:PGE:PVE; International audience; Ceria is a rather important material for applications in catalysis both as a catalyst and as a catalyst support. Although widely studied by TEM (Transmission Electron Microscopy) and despite an exhaustive literature on the structure of reactive facets of CeO2 correlated to its catalytic mechanisms, the temporal evolution of the atomic surface structure exposed to realistic redox conditions together with its possible influence on the supported metallic phases remains elusive. In order to contribute to a better understanding of the latter we present several studies performed within realistic gas environments in a dedicated FEI Titan 80-300 aberration-corrected environmental TEM. Firstly, we provide a direct visualization and quantification of the cationic mobility on (100) surfaces of CeO2 nanocubes in different controlled environments and achieve control of the surface dynamics under exposure to realistic gas atmospheres. In a second step we present the morphological, structural and chemical changes on metallic catalysts supported on ceria during redox cycles through two examples: (i) Ir/CeO2 used in the steam reforming of methane; we observed changes in size and morphology of Ir nanoparticles associated with modification of its catalytic behavior that could be associated with the existence of a metastable iridium sesquioxide phase never observed before. (ii) Pt/CeO2 used as a diesel oxidation catalyst; we evidenced a dynamic structural behavior of Pt nanoparticles on the ceria surface under reducing/oxidizing conditions at moderate temperatures where redispersion occurs in oxidizing atmospheres whereas Pt nanoparticles reform under reducing conditions leading to a protocol to control Pt particle formation.

MICROSCOPIE+ATARI:CARE:ECI2D+FCA:MAO:GFE:SLO:CGE:PVE:LMA:PGE; International audience; High spatial resolution studies of ceria and ceria based catalysts by aberration corrected Environmental Transmission Electron MicroscopyF.J. Cadete Santos Aires1, T. Epicier2, M. Bugnet2, M. Aouine1, Z.Wu3, A. Gänzler4, G. Ferré1, M. Casapu4, J.D. Grunwaldt4, S. Loridant1, C. Geantet1, P. Vernoux1, L. Massin1, P. Gélin11 Université de Lyon, UCBL Lyon 1, IRCELYON UMR 5256 CNRS, 2 Avenue Albert Einstein, 69626– Villeurbanne Cedex, France.2 Université de Lyon, INSA-Lyon, UCBL Lyon 1, MATEIS UMR 5510 CNRS, 7 Avenue Jean Capelle, 69626 – Villeurbanne Cedex, France.3 Chemical Science Division, Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.4 Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), Engesserstraße 20, 76131 Karlsruhe, Germany.Ceria (CeO2) is a rather versatile material extensively used in catalysis (as a catalyst or as a catalyst support) due to its redox properties and oxygen mobility capabilities. Despite exhaustive literature on its structural and chemical properties, in depth atomic scale surface analysis in environmental (realistic) conditions is lacking. This is essential to gain crucial, and otherwise unavailable, insight into the surface reactivity mechanisms driving the catalytic performance (activity, selectivity, stability, active sites and species, …). The advent of environmental transmission electron microscopes (ETEM) equipped withadvanced accessories such as an aberration corrector and a high speed camera opened these perspectives. It is now possible to follow in situ (variable P and T), almost in real-time and at subnanometer resolution the evolution of the morphology, the structure and the chemistry of the supported nanoparticles, of the support and of their interface. In particular, the termination of the surfaces, the mobility of the surface atoms, the local chemical composition and the redox state can be analysed down to the atomic level in most favourable cases.Here we present dynamic in situ studies dealing with issues directly related with the surface termination and mobility of ceria and with the evolution of metallic species supported on ceria for different catalyticapplications:(i) Atomic scale study of the surface mobility of CeO2 nanocubes under gaseous environments;(ii) Tuning in situ the noble metal dispersion in Pt/CeO2 diesel oxidation catalysts;(iii) Evolution of Ir/CeO2 catalysts during methane steam reforming.The studies were performed within the Ly-EtTEM (Lyon Environmental and tomographic Transmission Electron Microscope), a 80-300 kV TITAN objective lens Cs-corrected Environmental TEM from FEI, equipped with a GATAN high resolution Imaging Filter (GIF), a SDD XMaxN EDX spectrometer (Oxford Instruments) and a high-speed CCD Gatan OneViewTM camera, in varying pressure and temperature conditions using a Wildfire sample holder and SiNx nanochips from DENS Solutions.The authors are thankful for funding from INSA Lyon through a BQR project THERMOS, from the IMUST project at University of Lyon and IFPen (Solaize, F), from the German Federal Ministry for Economic Affairs and Energy (BMWi: 19U15014B) as well as from the DFG (High-Output Catalyst Development Platform, INST 121384/16-1), from the French National Research Agency for financial support of the ORCA and 3DCLEAN projects 14-CE22-0011-02 and 15-CE09-0009-0 respectively) and from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. The electron microscopy work presented here was performed on a FEI Titan ETEM at the Centre Lyon–St-Etienne de Microscopie (www.clym.fr).

ANALYSE:MICROSCOPIE+ATARI:CARE+DLG:MAO:LMA:PMA:PVE; International audience; 1.IntroductionCatalytic combustion of propane is a key reaction for power generation and engine exhausts control emissions. The interest for ceria-based materials as supports for PGM nanoparticles is growing due to their redox properties. The elucidation of Pd/ceria interactions is crucial to design a catalyst with optimum performances, find proper pretreatments that could boost catalytic performances or setting effective regeneration strategies. This study aims to investigate the impact of a reduction step in H2 at 500°C on the catalytic performance of Pd supported doped ceria catalysts in the propane combustion reaction. Two different oxides based on ceria zirconia (CZ), as a reference TWC support, and GDC, a mixed ionic electronic conductor, have been used to disperse Pd nanoparticles. The catalytic activity of the catalysts was characterized by stoichiometric C3H8 oxidation measurements. The samples were characterized by temperature programmed reduction, H2 static volumetric chemisorption, CO titration and XPS. In addition, the reduction step in H2 was in-situ observed by environmental transmission electron microscopy. Finally, the catalytic results obtained were compared with those of a Pd/ γ-Al2O3 reference catalyst.2.Experimental/methodologyPowdered catalysts were prepared by dispersing Pd nanoparticles (1 %wt.) on a GDC (Pd_GDC) (Ce0.8Gd0.2O2) and a CZ (Pd_CZ) (Ce0.62Zr0.38O2) powder using incipient wetness impregnation. C3H8 catalytic combustion was evaluated under stoichiometric conditions (2000 ppm C3H8 and 10000 ppm O2). The total flow was 300 Nml/h (GHSV=229.300 h-1). Prior to catalytic measurements, the samples were reduced under pure H2 (500 ºC, 1 hour). After cooling down to 25 °C in He, the flow was changed to the reaction mixture. The catalytic combustion of C3H8 was evaluated in two consecutive cycles. Between both cycles, the samples were left under one hour on stream at 500 °C and cooled down in the same reactive atmosphere. Reactants and products were recorded by an IR analyzer and a microGC.3.ResultsFigure 1.a depicts the light-off curves of the Pd_GDC and Pd_CZ catalysts. After the reduction step, catalytic performances of Pd_CZ are slightly better than those of Pd_GDC until reaching 10% of conversion. Then, the two light-off curves intersect and the catalytic properties of Pd_GDC become greater. After the stabilization step (one hour on stream at 500°C), the catalytic performances of the two catalysts drastically decrease. A third light-off curve was recorded (after a second reduction step) that shows that the catalytic performance of Pd_GDC was almost fully recovered. The impact of a reduction step in H2 has been in-situ observed by ETEM on both Pd_CZ and Pd_GDC catalysts (Figure 1b, 1c and 1d). Before reduction, it has been difficult to detect metallic particles (Figure 1.b), suggesting that most of the Pd is oxidized in accordance with TPR and XPS experiments. In H2 at 450°C, a re-dispersion of metallic Pd nanoparticles was observed. On GDC, Pd particles are more flattened shape rather than spherical particles and seem to be in strong interaction with the support (Figure 1.d).Figure 1.- a) Propane conversion curves for the Pd_GDC and Pd_CZ catalysts, and In situ ETEM for the b) Pd_CZ catalyst (20 °C, vacuum), c) Pd_CZ catalyst (450 °C, 1 mbar H2) and d) Pd_GDC catalyst (450 °C, 1 mbar H2)4.DiscussionThe results obtained in this study indicate a beneficial effect of the catalytic activity of the activation in H2 which might be linked to the stabilization, anchoring and high dispersion of metallic Pd particles onto the ceria surface upon reduction in linked with the surface reducibility of GDC and CZ confirmed by TPR experiments. On the other hand, after one hour on stream under the reacting mixture, the higher decay on the catalytic activity for the Pd_GDC catalyst was ascribed to a higher decoration of metallic nanoparticles inside the GDC support and/or by the formation of a Pd-ceria solid solution. This latter assumption is supported by TPR results, ETEM and XPS. Indeed, XPS spectra confirmed that Pd is predominantly in a solid solution form (PdxCeO2-δ), after oxidation step. 5.ConclusionThe catalytic activity can be strongly promoted by a reduction step at 500°C in H2. This effect was not observed on a non-reducible support such as alumina. Surface characterizations of the samples, including in-situ observations in H2 with an environmental transmission electron microscope, have shown that this activation process, in particular on GDC, is linked to the reduction of a surface interaction phase, PdxCeO2-δ. The surface reduction of this oxide allows to finely disperse metallic Pd nanoparticles. AcknowledgmentsThis work was performed in the “Triptic-H” project, partially funded by the French National Research Agency (ANR), ANR-2011-VPTT-003.

MICROSCOPIE+ATARI+LMA:MAO:PGE; National audience; None

+CDFA+WHN:MET:LMA:LCH:NES; International audience; None

International @ ECI2D+NTT:LMA:LBU:JMI; International audience; In the future, a strong increase in the demand for propylene is expected because of the growing markets for polypropylene and propylene oxide. In the other hand next generation of steam crackers will use shale gas ethane as raw material and less by-products will be available for propylene production. There is thus a need to develop bio-propylene. The later could be produce by dehydration of 1 or 2-propanol but contrarily to ethanol and 1-butanol, there are not large-scale industrial processes to produce them. One way to overcome this problem would be to produce propylene by metathesis from ethylene and 2-butene. The process would be economically attractive if 2-butene is produced by dehydration of 1-butanol, which is the isomer predominantly formed by fermentation and the number of reaction steps minimized. This can be done by running the dehydration of ethanol and 1-butanol in one step without water pre-separation. In this study, we report on the catalytic properties of rare earth phosphates tested for the dehydration of alcohols mixtures. The study of the catalytic properties of these solids has been extended to ABE (acetone-butanol-ethanol) mixtures produced by bacterial fermentation. Nd, Gd and Sm phosphates with Rhabdophane structure have been prepared by co-precipitation [1]. The acid-base properties of the catalysts have been studied by NH3- and CO2-TPD and Lutidine adsorption followed by IRTF to correlate these properties to the catalytic properties [2]. The phosphates have been tested in the dehydration of ethanol and 1-butanol mixtures (Fig.1). Activity in dehydration of ethanol was in the order: Gd>Sm>Nd but inverse for activity in 1-butanol and 2-butene selectivity. The results were from acid-base properties. Gd is more active for ethanol dehydration because it has more strong Br?nsted acid sites compared to Sm and Nd. But Sm and Nd have more weak and moderate acids sites, which make them more active to dehydrate 1-butanol and more selective to 2-butene. In any case, only 1-butene is formed besides 2-butene when 1-butanol is dehydrated. Since ethanol dehydration takes preferentially place on stronger acid sites, there is little competition between the reactions and total conversion of the 2 alcohols is observed. The catalysts were also shown to be very efficient to dehydrate ABE mixture (acetone, butanol, ethanol in 3-6-1 ratio).The conclusion of the work is that rare earth phosphates can dehydrate selectively alcohol mixtures or ABE mixtures produced by industrial fermentation processes. The catalysts are very selective for all alcohols in the same time and stable with time on stream. 1-butanol is preferentially dehydrated to 2-butene, which can be fruitfully used to transform ethanol 1-butanol mixtures and subsequently performed metathesis reaction to produce propene. Industrially they open the way to build a large-scale process to produce propene from alcohols minimizing purification/separation steps energetically costly.

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