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MICROSCOPIE+MEME+FCA:EEH:LBU:TEP; International audience; The di-block copolymer inverse micelle method, where an amphiphilic di-block copolymer dissolved in toluene creates a system of inverse micelles, is a rather simple method to obtain well controlled supported metallic nanoparticles once the micelle core is charged with metallic salts. Supported metallic catalysts can be obtained in this way on both flat (model catalysts) and powder (realistic catalysts) supports [1]. Our main interest deals with applications of bimetallic catalyst systems that we investigate from extended catalytic surfaces [2] to realistic catalysts [3]; the idea being to isolate and understand the role of important physico-chemical parameters on the catalytic behaviour of these systems in the shape of model catalytic surfaces and try to extrapolate them to realistic catalysts. This is very important for the controlled design of catalysts with specific properties. In this way we can, not only spend less active material (often rare and expensive), but also avoid unnecessary poisoning while keeping high activity (stability) and finely tune the selectivity to avoid deleterious unwanted products; these are important points to be able to achieve environmentally friendly and sustainable catalytic processes. Self-organized nanoparticles on flat surfaces is an intermediate configuration between extended catalytic surfaces and realistic catalysts and a necessary step to better extrapolate results between model and realistic systems. We have thus extended the di-block copolymer method to the synthesis of bimetallic catalysts [4]. In our presentation we will deal with a PdAu system, obtained from a PS-b-P2VP copolymer micellar solution that we transfer by spin-coating to a surface of a SiNx eletron-transparent films on dedicated microchips than are heated in Wildfire sample holder (DENS Solutions) within an objective lens aberration-corrected environmental TEM (Titan ETEM G2 80-300 kV from ThermoFisher Scientific) so that we can study in situ the behaviour of such a system in variable temperature and gas pressure. We observed the formation of the individual particles from the seeds within the core of the micelles in the presence of oxygen in variable temperature; sintering of the seeds within the micelle cores starts at 350°C and is completed at 500°C, temperatures that correspond, respectively, to the onset of the copolymer decomposition and to its quasi-completed decomposition [5]. We also observed that the network of nanoparticles is stable under oxygen up to 900°C and that, above this temperature, the network is modified only by the decomposition of the nanoparticles (when we approach their melting point).The authors acknowledge the French Microscopy and Atom probe network (METSA) and the Consortium Lyon – St-Etienne de Microscopie (CLYM) for supporting this work.References:[1] B. Roldan Cuenya, Accounts of Chemical Research 46 (2013) 1682.[2] MC Saint-Lager et al., ACS Catalysis 9 (2019) 4448.[2] B. Pongthawornsakun et al., Applied Catalysis A: General 549 (2018) 1.[4] E. Ehret et al., Nanoscale 7 (2015) 13239.[5] T. Orhan Lekesiz et al., Journal of Analytical and Applied Pyrolysis 106 (2014) 81.

MICROSCOPIE+MEME+EEH:TEP:MAO:LBU:FCA; International audience; We used self-assembled block copolymer templates to generate arrays of bimetallic nanoparticles. In this approach, a block copolymer consisting of hydrophilic and hydrophobic blocks is dissolved in a selective solvent such as toluene in order to obtain inverse micelles. The core of such inverse micelles can then be functionalized with metal precursors ligated by complexation or protonisation to the inner polymer block. The reverse micelles can then be transferred from the solution to the substrate by using, for instance, standard spin or dip coating techniques. The obtained layer exhibits a rather high degree of hexagonal order, reflecting the packing of spherical micelles.We present results on the formation of arrays of both PdAg and PdAu nanoparticles obtained by this method. For the latter a specific study on the stability of the array at high temperatures under oxygen pressure was performed within an objective-lens aberration-corrected environmental transmission electron microscope (Titan ETEM G2 80-300 kV from ThermoFisher Scientific).

MICROSCOPIE+MEME+EEH:FCA:LBU:TEP; International audience; Systems of self-organized nanoparticles (NPs) are useful in many domains such as, for instance, optics, nanostructure growth and, the domain of most interest in our case, catalysis. It is indeed a way to control the classic characteristics of catalysts (size, dispersion, chemical phase, …) and add a new tunable parameter, often poorly controlled, which is the long-distance ordering and, thus, the inter-nanoparticle distance. Well-controlled physicochemical properties of the catalysts lead to better correlation between these properties, their possible evolution, and their catalytic performance (activity, selectivity, stability). Among self-assembly techniques, the use of di-block copolymer method, where an amphiphilic di-block copolymer dissolved in toluene yields a system of inverse micelles, is a rather simple method to obtain well controlled supported NPs which can be used as supported metallic catalysts on both flat (model catalysts) and powder (realistic catalysts) supports [1]. After formation of the micellar solution, we can indeed charge the core with metal salts that can then be deposited on flat surfaces by dip or spin coating for instance. Our main interest deals with applications of bimetallic catalysts that we study in the form of both realistic catalysts [2] and extended catalytic surfaces [3]; self-organized NPs on flat surfaces is an intermediate configuration between these two approaches which is useful to better extrapolate results between model and realistic systems. With this in mind we have extended the di-block copolymer method to the synthesis of bimetallic catalysts [4]. For these systems composed of metals with different characteristics, several questions remain unanswered such as the evolution of the pre-formed bimetallic seeds (Fig. 1b-d) with temperature, the temperature formation of unique NPs at the micellar core or the stability of the network of bimetallic NPs (Fig. 1a) at high temperature in presence of reactive gases.An objective lens aberration-corrected Environmental TEM (Titan ETEM G2 from FEI/ThermoFisher Scientific), operated at 300kV and capable of gas pressure up to 20 mbar, is a well-adapted tool to study those phenomena. An Au-rich AuPd core-metallized PS-b-P2VP micellar solution was synthesized and deposited by spin-coating on dedicated heating microchips containing a silicon nitride electron transparent (discrete) film capable of reaching temperatures up to 1300°C within a WildFire support holder (DENS solutions). Special care was taken to minimize/prevent any influence of the electron beam on the observed events. In order to observe both the formation of the individual NPs, together with the elimination of the copolymer, and the high-temperature stability of the network we have worked under oxygen pressure (up to 2 mbar). We observed that the seeds within the micellar cores (Fig. 2a-left) begin to sinter around 350°C (Fig. 2a-center) which is consistent with the temperature onset at which the copolymer (associated to a metal) begins to decompose [5]; unique NPs are formed around 500°C (Fig. 2a-right), when the copolymer is almost completely gasified [5]. The network is remarkably stable up to 900°C (Fig. 2b); finally, around 1000°C, close to the melting temperature of Au (1064°C), the NPs begin to decompose (Fig. 2b). At 1100° C, unique Au-rich NPs (Fig. 3a) begin to shrink and yield smaller satellite NPs (Fig. 3b); then the facetted NP (Fig. 3c) becomes spherical (Fig. 3d) and finally disappears to leave only the satellite NPs that grow on the surface (Fig. 3e). The volume ratio between the satellite NPs and the initial Au-rich NP indicate that only the Au within the NP has disappeared and that the remaining satellite NPs are pure Pd. The stability of the network seems to depend only on the intrinsic properties of the chosen metals [6].References:[1] B Roldan Cuenya, Accounts of Chemical Research 46 (2013) 1682.[2] B Pongthawornsakun et al, Applied Catalysis A: General 549 (2018) 1.[3] MC Saint-Lager et al, ACS Catalysis 9 (2019) 4448.[4] E Ehret et al, Nanoscale 7 (2015) 13239.[5] T Orhan Lekesiz et al, Journal of Analytical and Applied Pyrolysis 106 (2014) 81.[6] The authors acknowledge the French Microscopy and Atom probe network (METSA) and the Consortium Lyon – St-Etienne de Microscopie (CLYM) for supporting this work.

MICROSCOPIE+CARE:MEME+ACV:LBU:MAO:PVE:FCA; International audience; Ethylene oxide (EO) is a chemical intermediate of paramount importance and it is one of the most produced petrochemicals. It is used as a precursor for the further production of added value molecules, including plastics, polyester and ethylene glycol [1]. The most widely used catalytic process for the production of EO is the partial oxidation (epoxidation) of ethylene with air (or oxygen) on Ag/α-Al2O3 catalysts at low reaction temperatures (220 – 280 °C) but at high pressures (10-30 Bar) [2]. In the absence of any chemical promoters, the selectivity towards EO is in the range of 50%; to enhance the efficiency of the epoxidation process, the addition of chlorinated hydrocarbons (e.g. dichloroethene or vinyl chloride) is known to improve the selectivity to values ~90 %. However, chlorinated promoters are not environmentally friendly, and their eventual accumulation leads to a significant poisoning of the catalyst.Following an alternative approach, Stoukides and Vayenas reported the promotional effect of O2- ions on an Ag catalyst film on Ag//YSZ (catalyst-electrode//solid electrolyte) electrochemical catalysts for ethylene epoxidation [3]. It was found that pumping O2- ions towards the Ag electrode via electrical polarization allowed to dramatically enhance the selectivity and yield of EO production at 400 °C and atmospheric pressure.The idea of this study is to take advantage of the main features of both the electrochemical catalysts (i.e., the possibility to in situ supply O2- promoters) and the conventional industrial catalysts (i.e., higher metallic dispersion and accessibility to active sites). We studied the ethylene epoxidation reaction on Ag/YSZ composites supported on dense yttria-stabilized zirconia (YSZ) solid electrolytes at atmospheric pressure and in the absence of chlorinated promoters. The experiments performed showed a dynamic performance, where the activity evolved with time in an unprecedented manner. Before reaching a “steady-state” (with EO selectivity lower than 10 %) the system passed through an “optimized state”, where the EO selectivity was ~ 40-50 %. The pretreatment of the catalyst under oxidizing and reducing atmospheres, the influence of the oxide support (Gd-doped CeO2 and α-Al2O3) and the impact of the catalyst loading were studied. In addition, in situ electron scanning and transmission microscopy observations were performed on the Ag/YSZ composite. All these experiments suggest that the “optimized-state” takes place due to the production of small silver clusters formed after the evaporation, decomposition and further condensation of AgxO species from the bulk of the composite to the YSZ powder. The activity of these Ag clusters species would be dramatically enhanced due to the promotional effect of the O2- ions supplied by the YSZ support, due to metal-support interactions. However, once the YSZ support is saturated with Ag clusters, they start to agglomerate, leading to bigger nanoparticles with lower selectivity towards the desired EO product. This study clearly demonstrates therefore the possibility to use active catalytic supports (e.g. YSZ) to drastically enhance, in a significant manner, the performance of Ag catalysts for the ethylene epoxidation reaction without the addition of non-environmentally-friendly chlorinated promoters (commonly used for industrial applications). Also, to the best of our knowledge, the use of Ag/YSZ catalysts (without electrical polarization) has never been reported for ethylene epoxidation.This work is part of the “EPOX” project funded by the French National Research Agency, ANR-2015-CE07-0026.References1.Özbek, M.O.; van Santen, R.A. Catal. Lett. 2013, 143, 131–141.2.Chongterdtoonskul, A.; Schwank, J.W.; Chavadej, S. J. Mol. Catal. A-Chem., 2012, 358, 58–66.3.Stoukides, M.; Vayenas, C.G. J. Catal. 1981, 70, 137–146.

SSCI-VIDE+MEME+FCA; International audience; .The size, structure, dispersion, and distribution of Pt entities (atomic species/cations, nanoparticles, rafts) on ceria appears to vary and evolve during reducing/oxidizing cycles even at moderate temperatures [1,2]. From these observation arises the concept of dynamic catalysts that can be used to tailor, stabilize and /or modulate their catalytic properties by using appropriate treatments. Taking advantage of the possibility of working under gas pressure and temperature variable conditions in the Ly-EtTEM [3] during imaging/analyses at high spatial (atomic) and temporal resolution (~10 msec), we illustrate this approach with two studies performed over Pt/CeO2 catalyst with potential application in diesel post-combustion.AknowledgementsThis work is a team effort and would not have been possible without the input of my colleagues from IRCELYON/Villeurbanne-France (G. Ferré, L. Burel, M. Aouine, F. Bosselet, S. Ntais, T. Epicier, C. Geantet S. Loridant, P. Vernoux) and from ITCP-KIT/Karlsruhe-Germany (A. Gänzler, F. Maurer, M. Casapu, J.-D. Grunwaldt. The Consortium Lyon-St-Etienne de Microscopie (CLYM) is thanked for the access to the Ly-EtTEM.References[1] A.M. Gänzler, M. Casapu, P. Vernoux, S. Loridant, F.J. Cadete Santos Aires, T. Epicier, B. Betz, R. Hoyer, J.-D. Grunwaldt, Angewandte Chemie International Edition 56 (2017) 13078–13082. DOI: 10.1002/anie.201707842[2] G. Ferré, M. Aouine, F. Bosselet, L. Burel, F.J. Cadete Santos Aires, C. Geantet, S. Ntais, F. Maurer, M. Casapu, J.-D. Grunwaldt, T. Epicier, S. Loridant, P. Vernoux, Catalysis Science & Technology, 2020, DOI: 10.1039/d0cy00732c.[3] The Ly-EtTEM (Lyon Environmental and tomographic TEM) is a FEI Titan ETEM G2 corrected for the aberrations of the objective lens installed at CLYM (Consortium Lyon–St-Etienne de Microscopie) in Lyon.

SSCI-VIDE+MEME+FCA; International audience; Manganese oxides are promising candidates to create new catalysts possessing activity in a relatively lowtemperature oxidation of formaldehyde and CO. Such materials are widely used in oxidative processes due to high oxygen mobility associated with the presence of redox pair of Mn(IV)/Mn(III), existing as oxygen vacancies [−Mn3+−□−Mn3+−]. A prospective way to further improve the catalyst performances is manganese oxide modification with transition metal cations or variable valence cations [1, 2]. The CO oxidation reaction is widely used as a test process for solving fundamental problems in the field of heterogeneous catalysis [3–4], being an effective tool for studying the dependence of catalytic activity on structural features of material, e.g. the size, morphology, states of modifying cations/clusters/nanoparticles [5–6].The aim of this work is to study the synergetic effect between transition metal modifier (Fe3+, Sn4+, Ce4+) in CO oxidation process. All catalysts were characterized by BET, TEM (HRTEM), XRD, Raman and long-tested in CO oxidation process for 100 h to obtain TOS curves. Catalyst samples were prepared using a redox reaction between required amount of Mn(NO3)2 and KMnO4 according to procedure reported in [2]. According to XRD data, α-MnO2 crystalline phases were primarily formed for unmodified sample, Fe- and Sn modified samples. For Ce-modified catalyst β-MnO2 crystalline phases were prevailed. No reflexes of iron and cerium oxides were observed in the diffractograms of the Fe- and Ce-modified samples suggesting high dispersion of such phases. In Sn–MnO2 sample a dispersed SnO2 phase was identified. The lattice-resolved HRTEM showed the regular lattice arrangement of α-MnO2 and β-MnO2 for nanorod particles of unmodified sample. TEM images indicate nanorod, spindle-shaped and shapeless particles for Fe–MnO2, the nanorod particles and 3–7 nm nanoparticles agglomerated or located on the nanorod particles for Sn–MnO2 and nanorod particles and agglomerates of shapeless particles for Ce–MnO2. The TEM data indicates the incorporation of Ce in the manganese oxides rather the formation of CeO2 phase for Ce-modified sample, which comes in agreement with XRD data.Catalytic testing in CO oxidation process was carried out in quartz reactor according to procedure described in [7]. Catalysts were tested for 100 h. The temperature increased from 50 to 125 °C for Ce–MnO2 and to 145 °C for other catalysts. The molar ratio of O2/CO was 8, GHSV = 36000 h-1. It was shown that the introduction of the transition metal into the composition of MnO2 with the OMS-2 structure allowed increasing the activity of catalysts: MnO2 < Sn–MnO2 £ Fe–MnO2 < Ce–MnO2. All catalysts were stable in CO oxidation process during 100 h.Therefore, catalysts based on manganese oxides modified with Fe, Sn or Ce possess good catalytic properties in CO oxidation and are promising candidates to create effective oxide catalysts. Further research will focus on investigation of Fe- and Ce-containing OMS-2 catalysts modified by bimetallic (Ag–Pd) nanoparticles.This research project is supported by Russian Science Foundation (project 19-73-30026).References1. Sultana, S.; Ye, Z. et al. Catal. Today 2018, 307, 20.2. Dotsenko, S.S.; Verkhov, V.A. et al. Catal.Today 2019, in press.3. Kropp, T.; Mavrikakis, M.; J. Catal. 2019, 377, 577.4. Royer, S.; Duprez, D. Chem.Cat.Chem. 2011, 3, 24.5. Nikolaev, S.A.; Golubina, E. et al.; Kinet. Catal. 2014, 55, 311.6. Gordon, E. B.; Karabulin, A. V. High Energy Chem. 2016, 50, 305.7. Grabchenko, M. V.; Mamontov, G. V. et al. Appl. Catal. B: Environmental 2020, 260, 118148.

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:RX+ATARI:CARE:ECI2D+MAO:FBS:FCA:CGE:SLO:PVE; International audience; Nowadays, design of new catalysts has to take into account scarcity of sensitive elements especially noble metals. When decreasing metal loading over a support to address this scarcity, new types of catalytic sites (single atoms, subnanometric clusters) can be stabilized [1]. Such highly dispersed sites have to be more efficient as their number is limited at low loading. Furthermore, the interface between such highly dispersed sites and the support plays a key role since it determines their thermodynamic stability for a given atmosphere as well as their electronic and catalytic properties. We have recently demonstrated the dynamic nature of Pt NPs supported on ceria under reducing/oxidizing sequences at temperatures below 500 °C [2]. This concept of dynamic catalysts can be used to tailor and stabilize more efficient catalytic sites by applying appropriate treatments.This work aims to get new insights into the impact of redox sequences on the Pt/CeO2 interactions for tailoring DOC catalysts. A Pt/CeO2 catalyst containing single-atom Pt was prepared and exposed to model redox sequences in H2/O2 at mild temperatures. The catalyst was reduced either at 250 °C or 500 °C to get different kinetics of the dynamic Pt NPs construction. Then, it has been re-oxidized at three different temperatures (RT, 250 °C, 500 °C) to modulate the redispersion rate. Combined characterization techniques were implemented such as HAADF STEM microscopy, in-situ Raman spectroscopy, in-situ XRD, XPS, CO-FTIR and H2-TPR to deeply characterize the catalyst after redox sequences, in connection with its catalytic activity for CO, NO and propene oxidation in a simulated lean exhaust containing water.Stabilization of raft-like Pt clusters of ca 1 nm diameter in strong interaction with CeO2 was evidenced after redox sequences at 250 °C without Pt incorporation into the CeO2 bulk. These particular sites appeared an intermediate state between single atoms and 3D particles with suitable properties for CO adsorption. They were essentially observed after the 250 °C/RT sequence for which CO was converted at low temperature. Furthermore, the 250 °C/RT sequence was shown to strongly improve CeO2 reducibility and to stabilize new sites containing Pt2+, Ce4+ cations and peroxo species that could be located at the Pt raft/CeO2 and involved in the reaction mechanism. Finally, a new methodology using in situ Raman mapping showed that dynamics between Pt single atoms and 3D particles take place at the microscale, i.e. at the powder grain scale. [1] J. Jones, H. Xiong, A.T. DeLaRiva, E.J. Peterson, H. Pham, S.R. Challa, G. Qi, S. Oh, M.H. Wiebenga, X.I. Pereira Hernández, Y. Wang, A.K. Datye, Science, 2016, 353, 6295.[2] A.M. Gänzler, M., Casapu, P. Vernoux, S. Loridant, F.J.C.S. Aires, T. Epicier, B. Betz, R. Hoyer, J.-D. Grunwaldt, Angew. Chem. 56 (2017) 13078-13082.

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SSCI-VIDE+ATARI+FCA; International audience; Environmental TEM dynamic high spatial resolution studies of surface mobility on ceria nanocubes and of metal/ceria supported catalysts evolution during redox cyclesF.J. Cadete Santos AiresIRCELYON – UMR5256 CNRS/Univ. Lyon1. 2, Av. Albert Einstein. 69626 – Villeurbanne. France.Ceria is, in one hand, a fascinating material from the point of view of fundamental studies and, in the other hand, a rather important material for applications in catalysis both as a catalyst and as a catalyst support. Although widely studied by TEM 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 its possible influence on the supported metallic phases remains elusive.In a first step, we provide a direct visualization of the atomic mobility of cerium atoms on (100) surfaces of CeO2 nanocubes in high vacuum, O2 and CO2 atmospheres and by quantifying the cationic mobility, we achieved control of the surface dynamics under exposure realistic gas atmospheres, yielding new information for a better understanding of the intimate catalytic mechanisms.In a second step we present rather morphological, structural and chemical changes on metallic catalysts supported on ceria during redox cycles. Ir/CeO2 is used in the steam reforming of methane and the observed changes in size and morphology of Ir nanoparticles associated with modification of the catalytic behavior of the catalyst could be associated with the existence of a metastable iridium sesquioxide phase. We provide structural information for this phase, that has never been experimentally identified before, and for which only theoretical suggestions have been made on its structure. Pt/CeO2 is 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 (< 500°C) where redispersion occurs in oxidizing atmospheres whereas Pt nanoparticles reform under reducing conditions. A protocol was devised to control Pt particle formation and thus enhance the catalytic activity of Pt/CeO2-based exhaust gas catalysts.The surfaces of CeO2 nanocubes and the Ir/CeO2 and Pt/CeO2 catalysts were studied, within realistic gas environments well-adapted for each mentioned application, in a dedicated FEI Titan 80-300 environmental TEM (ETEM) operated at 300 kV and equipped with a Cs-image corrector, a high-speed Gatan CMOS OneViewTM camera, an Oxford Instruments SDD XMaxN EDX spectrometer and a Tridiem ERS Gatan Imaging Filter (GIF).The author warmly acknowledges the invaluable contributions of T. Epicier, M. Bugnet, L. Roiban (MATEIS, F) and M. Aouine (IRCELYON, F) to the ETEM study and F. Meunier, P. Gélin, L. Massin, P. Vernoux, S. Loridant, C. Geantet, G. Ferré (IRCELYON, F) and A.M. Gänzler, M. Casapu, J.D. Grunwaldt (KIT, D) for the supported catalysts preparation and fruitful discussions.

MICROSCOPIE+ATARI:CARE:ECI2D+GFE:MAO:FCA:CGE:SLO:PVE; International audience; The shape, size and electronic properties of Pt nanoparticles supported on ceria have been tailored during model redox sequences based on successive H2 (reduction) and O2 (oxidation) 1 hour treatments at moderate temperatures (250 °C and 500 °C). Raft shaped Pt nanoparticles of around 1 nm size are produced on the surface, in strong interaction with ceria, then boosting the oxygen transfer from the oxide towards Pt. In situ techniques establish the presence of Pt cations in an intermediate oxidation state, probably Pt2+, in interaction with peroxo oxygen species.

MICROSCOPIE+ATARI:CARE:ECI2D+GFE:MAO:FCA:CGE:SLO:PVE; International audience; 1.IntroductionThe tailoring of Pt based diesel oxidation catalysts is crucial to enhance the efficiency of the diesel vehicles after treatment. For instance, specific interactions between Pt and ceria can improve the thermal stability of Pt nanoparticles (NPs) in an oxidizing atmosphere as in diesel exhausts, through the formation of rigid Pt-O-Ce bonds.1 More recently, Jones et al.2 have evidenced stabilization of Pt single atoms and clusters on ceria surface steps, strongly suggesting the doping of ceria subsurface by Pt cations in good agreement with DFT studies3 which also predict Pt2+ cations incorporation between surface oxygen ions species of the support. We have recently demonstrated the dynamic nature of Pt NPs on ceria under reducing/oxidizing sequences at temperatures below 500 °C.4 Lean/rich pulses can be used to control the formation of Pt NPs and enhance their catalytic activity for CO oxidation.4 This study aims at getting new insights into the impact of redox sequences on the Pt and CeO2 interactions.2.Experimental/methodsCeria provided by Solvay Special Chem. Company was dry impregnated with Pt (0.9 wt %) and calcined 4 h at 500 °C. Before each characterization or catalytic test, the catalyst was systematically pretreated in O2 for 1 h at 500 °C to get a reference state. Model redox sequences were composed of a first reduction step of 1 h in 10% H2 followed by an oxidation one also of 1 h in 20% oxygen. They were performed at different temperatures: 500/500 °C (reduction/oxidation), 250/250 °C and 250 °C/RT. Catalytic performances were measured for CO and propylene oxidation in a lean mixture (10% O2, 1000 ppm CO, 500 ppm NO, 500 ppm C3H6, 10% H2O in He) that simulates diesel exhaust gas. Temperature-Programmed Reduction (TPR) experiments were conducted with a Inficon JPC400 mass spectrometer. STEM observations were performed with an Environmental Transmission Electron Microscope (Ly-ETEM, FEI TITAN ETEM operated at 300 kV). The spatial distribution of surface oxygen electrophilic species and PtOx clusters were assessed by Raman spectroscopy mapping at the micrometric level (200 µm x 200 µm) recorded at RT under oxygen flow. HRXANES was also implemented to in situ follow the oxidation degree of Ce cations in the catalyst.3.Results and discussionAs previously observed with rich/lean pulses,4 model redox sequences can achieve outstanding catalytic performances for CO and C3H6 oxidation, much higher than those recorded at the reference state. TPR experiments have shown that model redox sequences increase the reducibility of ceria. The H2 consumption only starts above 150 °C on the first TPR, suggesting the absence of Pt NPs able to chemisorb H2 below this temperature, as confirmed by STEM observations. Successive redox sequences (TPR 2 and TPR 3) promote the formation of Pt NPs in strong interaction with ceria as shown by the excellent reducibility of the support as early as the room temperature. The lower the temperature of the redox sequences, the greater the reducibility. Variations of the Raman band associated with PtOx at 690 cm-1 demonstrate that such species evolve upon redox sequences with stabilization of Pt cations in another oxidation state, probably Pt2+, as suggested by XPS measurements and DFT calculations.3 These Pt2+ cations are in interaction with peroxo oxygen species (Raman bands at 860 cm-1). No Ce3+ cations were detected both by electronic Raman spectroscopy and HR-XANES measurements, confirming that these oxygen peroxo species did not re-oxidized ceria but are stabilized on the surface.The shape of the Pt NPs was followed along the redox sequences. After the first reduction step, only raft shaped particles or single atoms are observed on the surface (Fig. 1c). This morphology is not modified after a subsequent oxidation step but the surface mean diameter of Pt rafts slightly increases from 1.0 to 1.3 nm, maybe due to Pt oxidation. Statistics on the ratio between the number of rafts and single atoms were tricky to estimate. However, CO chemisorption performed after each reduction step shows no significant modification of the Pt dispersion along the redox cycles.4.ConclusionsThis work showed that raft shaped Pt nanoparticles in closed interaction with ceria can be stabilized by model redox sequences at mild temperatures. This maximizes the Pt/ceria interface, promoting the oxygen transfer from the support towards Pt which is a key step in the CO oxidation mechanism. Pt cations are stabilized in an intermediate oxidation state, probably Pt2+, in interaction with peroxo oxygen species, confirming the high availability of oxygen species for oxidation reactions.AcknowledgementFrench National Research agency ‘Agence Nationale de la Recherche’ (ANR), project ORCA (ANR-14-CE22-0011-02) and German Federal Ministry for Economic Affairs and Energy (BMWi) are acknowledged for their financial support. The authors thank Solvay Special Chem Company for material contribution and the CLYM for access to the Ly-EtTEM.References[1]Y. Nagai, K. Dohmae, Y. Ikeda, N. Takagi, T. Tanabe, N. Hara, G. Guilera, S. Pascarelli, M.A. Newton, O. Kuno, H. Jiang, H. Shinjoh, S. Matsumoto, Angew. Chem., 2008, 47, 9303-9306.[2]J. Jones, H. Xiong, A.T. DeLaRiva, E.J. Peterson, H. Pham, S.R. Challa, G. Qi, S. Oh, M.H. Wiebenga, X.I. Pereira Hernández, Y. Wang, A.K. Datye, Science, 2016, 353, 6295.[3]A. Bruix, Y. Lykhach, I. Matolínová, Armin Neitzel, T. Skála, N. Tsud, M. Vorokhta, V. Stetsovych, K. Ševčiková, J. Mysliveček, R. Fiala, M. Václavů, K.C. Prince, S. Bruyère, V. Potin, F. Illas, V. Matolin, J. Libuda, K.M. Neyman, Angew. Chem., 2014, 53, 10525-10530.[4]A.M. Gänzler, M., Casapu, P. Vernoux, S. Loridant, F.J.C.S. Aires, T. Epicier, B. Betz, R. Hoyer, J.D. Grunwaldt, Angew. Chem., 2017, 56, 13078-13082.

SSCI-VIDE+ATARI+FCA; International audience; The seminar will deal with the complementary information on CO oxidation performed on bimetallic surfaces (PtSn (111) and PdAu (110) and gathered by surface science methods (STM, NAP-XPS, PM-IRRAS, SXRD) in realistic conditions (P and T variable)

MICROSCOPIE+ATARI:CARE:ECI2D+GFE:MAO:FCA:CGE:SLO:PVE; International audience; Due to European regulation on car exhausts, NOx emissions must be cut down. NOxTrap system stores NOx during lean phase as nitrates and during short rich phase triggered by pulses of gasoil, nitrates are decomposed and NOx reduced into N2. Our objective is to combine DOC (Diesel Oxidation Catalyst) and NOx storage-reduction in one catalytic system. This study reports the effect of redox rich/lean cycles on the catalytic activity of a model catalyst, Pt/CeO2. This activation step provokes a huge improvement of the catalytic performances for hydrocarbon and CO oxidation. Raman and ETEM experiments indicate a modification of platinum nanoparticles (NPs) dispersion on ceria at both micrometric and nanometric scales.1. ScopeEuropean environmental regulations on NOx emissions of mobile sources are becoming more and more severe. NOxTrap catalyst is one of the solution to reduce NOx into N2 under lean-burn conditions, such as for diesel engines. NOxTrap system works in cyclic gas-composition conditions. During the first step (lean phase), NOxTrap catalyst stores emitted NOx as nitrates until the surface reaches the saturation threshold. Then a pulse of fuel post-injection triggers the short second step (rich phase), during which the reducing conditions lead to nitrates decomposition, release as well as subsequent NOx reduction into N2 and surface regeneration. NOxTrap catalysts are commonly composed of Pt for its oxidative properties during lean phases; Rh to reduce NOx during rich phases; an alkaline compound as barium oxide and an oxide support. Ceria offers a high specific surface area support for metal dispersion, especially Pt, even at high temperature due to the strong interaction between Pt and CeO2.1 At low temperature (below 200 °C) its NOx storage capacity is higher than that of barium oxide.2 Our objective is to combine the oxidation function (DOC) and the NOx reduction ability into a single catalytic system through a fine NOxTrap catalyst formulation tuning. This study aims to understand the effect of redox rich/lean cycles at 250°C on the catalytic activity of a model catalyst, Pt/CeO2 (1wt% Pt) through in-situ characterizations. 2. Results and discussionCeria provided by Solvay Special Chem. Company was impregnated with platinum (1 wt %) by Umicore and then calcined 2 h at 500 °C. Catalytic performances show an important shift to lower temperatures of CO and C3H¬6 conversion after 1 h of cycles between lean (90 sec, 10% O2, 500 ppm NO, 1000 ppm CO, 500 ppm C3H6, 10 %H2O in He) and rich (30 sec, 2% CO in He) at 250 °C (figure 1) which simulates the NOxTrap process. Similar activation steps were achieved for lean/rich sequences up to 500°C. The origin of this activation was studied by in-situ Raman spectroscopy and Environmental Transmission Electron Microscopy (ETEM, FEI TITAN ETEM G2 80-300 kV and DENS Solution heating sampled holder) after rich/lean sequences at 500°C. Ceria defect band and platinum oxide dispersion was assessed by Raman spectroscopy mapping at the micrometric level (200 µm x 200 µm). Platinum oxides re-dispersion and increase of lattice defect in ceria were both highlighted after lean/rich sequences (Figure 2). ETEM was complementary used to in-situ follow the Pt NPs dispersion on ceria during lean (O2, 10 mBar)/rich (H2, 10 mBar) sequences at 500°C. Several areas of the catalyst were observed to achieve statistical data on the Pt NPs size distribution (Figure 3). Under O2, we have observed the disappearance of most of the small Pt NPs while the consecutive rich sequence evidenced their reappearance but not necessary at the same position. The comparison of the Pt NPs size distribution highlights the impact of lean/rich treatments on the Pt/CeO2 interactions. 3. ConclusionsIn-situ characterizations of a Pt/CeO2 catalyst by using Raman spectroscopy and Environmental TEM have clearly shown that rich/lean sequences can strongly modify the Pt NPs distribution on the support both at the micrometric and nanometric levels. Such a redox sequence seems to optimize the Pt dispersion on the ceria and consecutively improve the catalytic properties.Figure 2 : Comparison of the intensity distributions during mapping of (A) the PtOx band area at 690 cm-1 and (B) the lattice defect band area at 250 cm-1 at initial oxidized state (blue) and after two cycles of reduction ( 10% H2 – 500 °C – 1 h ) and oxidation (20 % O2 – 500 °C – 1 h) (orange). Figure 3 : ETEM pictures of one catalyst area during lean/rich sequences at 500 °C. White arrows indicate relevant NPs modifications.AcknowledgmentFrench National Research agency ‘Agence Nationale de la Recherche’ (ANR), project ORCA (ANR-14-CE22-0011-02) and German Federal Ministry for Economic Affairs and Energy (BMWi) are acknowledged for their financial support. The authors thank Solvay Special Chem. Company for material contribution and the CLYM for access to the Ly-EtTEM. References 1. R. Hoyer, A. Schuler, S. Franoschek, T.R. Pauly, G. Jeske, WO 2013/149881 A1, October 22, 20142. E. Rohart, V. Bellière-Baca, K. Yokota, V. Harlé, C. Pitois, Top. Catal. 2007, 42-43, 71–75.

International audience

SSCI-VIDE+ATARI:CARE:ECI2D+PVE:GFE:SLO:FCA; International audience; None

MICROSCOPIE+ATARI:CARE:ECI2D+GFE:MAO:FCA:CGE:SLO:PVE; National audience; Depuis plusieurs années, les normes européennes des émissions de NOx des véhicules diesel ne cessent de se renforcer. Plusieurs solutions ont été mises en place par les équipementiers pour relever le défi de la réduction des NOx en N2 dans l’environnement oxydant des échappements diesel. Le système de stockage et réduction des NOx, appelé NOxTrap, est un procédé cyclique entre des phases de stockage des NOx sous forme de nitrates (phase pauvre) jusqu’à saturation de la surface du catalyseur et des phases riches de quelques secondes déclenchées par une post-injection de gazole qui permettent la décomposition des nitrates et la réduction des NOx en N2 en régénérant ainsi la surface. Les catalyseurs NOxTrap sont généralement composés de Pt pour la fonction oxydation lors des phases pauvres, de Rh pour réduire les NOx au cours des phases riches, d’un composé basique pour le stockage des NOx comme l’oxyde de baryum et d’un support oxyde. L’utilisation de la cérine comme support offre l’avantage d’assurer une bonne dispersion des métaux, notamment du Pt, même à haute température grâce à la forte interaction Pt/CeO2. D’autre part, la cérine permet un stockage des NOx plus important que l’oxyde de baryum à des températures inférieures à 200 °C. Notre objectif technologique est de regrouper la fonction d’oxydation des imbrulés (DOC : Diesel Oxidation Catalyst) avec celle de réduction des NOx dans une seule brique catalytique en adaptant la formulation d’un catalyseur NOxTrap. Cette étude expose l’impact des cycles pauvre/riche du système NOxTrap sur la fonction d’oxydation catalytique des imbrûlés (hydrocarbures, CO) d’un catalyseur modèle Pt/CeO2 (1% Pt). La mesure des performances catalytiques a montré une forte diminution de la température de conversion du CO et du C3H6 après une séquence d’une heure de cycles pauvre (90 s) /riche (30 s) à 250 °C sensée simuler le fonctionnement NOxTrap. L’origine de cette activation a été étudiée in-situ par microscopie électronique en transmission environnementale (ETEM) et par spectroscopie Raman. L’ETEM a mis en évidence la redispersion des nanoparticules de Pt à l’échelle nanométrique suite aux enchainements de phases riches et pauvres. Des cartographies Raman in-situ réalisées au cours des cycles redox ont permis de montrer que les processus de diffusion liés à la redispersion des atomes de platine à la surface de la cérine s'opéraient à l'échelle micrométrique et induisaient une augmentation de la quantité de ses défauts structuraux. Une séquence redox à 250 °C permet d’optimiser la dispersion du Pt sur la cérine et par conséquent d’augmenter significativement l’activité catalytique du catalyseur pour les réactions d’oxydation.

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).

SSCI-VIDE+ATARI+FCA; International audience; Predictability in science advances and their transfer to industrial application has been a constant concern for decision makers whether they are scientific researchers, industrialists or politicians. Research history has shown however that many forecasted successes never became actual industrial applications and many unforeseen developments became huge successes for industry and society.In the field of catalysis some hot topics are now being tackled and seem promising for future up scaling such as predictive catalysis (theory), nanostructured materials, single-site catalysis, single-atom catalysis, gold catalysis, advanced operando visualization of catalysts, VOC abatement, carbon dioxide capture, hydrogen production, biofuels, biomimetics,…Some of the above mentioned subjects will be critically analyzed.

International audience

Conférence, SSCI-VIDE+ATARI+FCA; International audience; None

MICROSCOPIE+ATARI:ING+FCA:MAO:CDA:FRM:DFA; International audience; None

MICROSCOPIE+ATARI:ECI2D:ING+FCA:MAO:SLO:ATU; International audience; None

MICROSCOPIE+ATARI:CARE+MAO:FCA:PVE; International audience; None

National @ CARE+ASR:MAO:FCA:PVE; International audience; Depuis 2011 (norme EURO 5), l'utilisation d'un filtre à particules (FAP) à l'échappement de tous les véhicules Diesel est obligatoire. La présence du FAP permet de grandement diminuer les émissions de particules. Cependant, le filtre doit être régénéré après un certain temps d'utilisation. Cette étude porte sur l'utilisation d'un catalyseur conducteur ionique : la zircone yttriée (YSZ) pour oxyder la suie. Cette céramique, stable chimiquement et thermiquement, est capable d'oxyder la suie via les ions oxygènes de son réseau selon un mécanisme électrochimique de type pile à combustible [1]. Afin de préciser le mécanisme d'oxydation des suies par les ions oxygènes, nous avons réalisé des observations in-situ, à l'aide d'un microscope électronique en transmission environnemental (METE, FEI TITAN), d'un mélange de suie et de catalyseur. Chauffé à 550°C sous vide, aucune oxydation de la suie n'a été observée. Une faible pression d'oxygène a ensuite été introduite, permettant de visualiser in-situ l'oxydation des particules. De nombreuses séquences vidéo ont été réalisées avec une résolution de 1 nm (figure 1). Les résultats soulignent l'importance du contact suie-catalyseur, la réaction d'oxydation se produisant à l'interface suie/catalyseur. Les particules de suie sans contact avec les grains de YSZ ne sont pas oxydées même après plusieurs minutes (figure 1, d). Lors de l'oxydation, les particules de suie se déplacent dans la direction du catalyseur et sont consommée à l'interface. Les lignes de contact entre le catalyseur et les particules de suie ont été estimées entre 20 et 40 nm. Des observations haute résolution ont permis de démontrer que la surface du catalyseur reste inchangée avant et après oxydation. Les différentes observations de l'oxydation de la suie à l'interface suie-catalyseur confirme l'hypothèse selon laquelle le mécanisme d'oxydation fait intervenir les oxygènes du réseau plutôt que ceux du milieux gazeux, en bon accord avec des expériences d'échange isotopique de l'oxygène.

Conférence @International @ ATARI+FCA; International audience; None

MICROSCOPIE+ATARI+EEH:NSP:MAO:FCA; International audience; None

MICROSCOPIE+ATARI:CARE+ASR:MAO:FCA:PVE; International audience; None

SSCI-VIDE+ATARI+FCA:NSP; International audience; None

International @ SURFACES+FCA; International audience; None