Search

Photoelectrocatalytic (PEC) glycerol oxidation is a promising technology for the simultaneous valorization of biomass waste and hydrogen generation. However, very few PEC studies have accomplished the selective production of value-added oxidation chemicals such as glyceraldehyde or dihydroxyacetone (DHA), especially under near-neutral conditions. 1 Herein, we report the outstanding PEC activity and stability of a monoclinic WO3 catalyst synthesized by a simple hydrothermal method for the selective generation of these C3 chemicals with simultaneous hydrogen generation. The joint selectivity of glyceraldehyde and DHA, among all liquid products, remained above 87% in a wide potential range (0.5-2.0 V vs. RHE) in a traditional 3-electrode PEC cell. Compared to the pure photocatalytic (PC) process, glyceraldehyde and DHA production were enhanced up to 4.5 and 11.5 times, respectively, by means of the external bias, with a stable faradaic efficiency above 50% of the additional holes hypothetically generated, in the whole studied potential range. Through different characterization techniques and the comparative analysis of the results obtained with a commercial WO3/TiO2 catalyst, the influence of the applied potential and the catalyst activity for water oxidation in the glycerol reaction mechanism are discussed, as well as the key role of the sub-stoichiometric tungsten oxide content and the corresponding catalyst oxygen vacancies, which confer very advantageous properties to WO3-based materials for the selective PEC valorization of glycerol. Furthermore, a proton-exchange membrane (PEM) PEC reactor was applied to achieve the spatial separation of glycerol oxidation to 3C products glyceraldehyde along with DHA in the anodic compartment and simultaneous hydrogen generation in the cathodic compartment. Three key parameters of light, external voltage, and temperature on PEC performances were explored by optimization of working conditions as well as the comparisons of pure PC, (thermal)catalytic (TC) and electrocatalytic (EC) activities. The unprecedented high selectivity of glyceraldehyde and DHA with the improved current was achieved with UV irradiation at 1.2 V of cell potential under 60 oC.

Hydrogen is an essential industrial target area, not only because of its use as an energy carrier and practical employment in fuel cells but also for its role as a significant raw material of the chemical industry [1]. Hydrogen can be produced by different processes (CH4 reforming being the most common), but the electrolysis of water is called to be an environmentally friendly solution. This process has taken force lately because it can be easily integrated to the electrical grid and use renewable energy sources (i.e. solar or wind) to produce pure H2 from water, producing only O2 as a by-product [2]. However, the thermodynamic cell voltage to achieve the water electrolysis reaction is around 1.23 V at room temperature [3]. Consequently, different strategies have been proposed to electrolyze organic molecules instead of water at the anode of low-temperature electrolyzers to reduce the energy demand. Plastic wastes contain an abundant source of hydrogen can be a promising renewable feedstock for electrolysis. A handful of studies have been published on this approach. Among them, our group published two studies considering the electro-reforming of poly(methyl methacrylate) (PMMA) [4,5]. Even if some initial findings demonstrate the proof-of-concept, several limitations were found: accumulation of species at the anode and poisoning. Moreover, the fact of having only C-C bonds in the main PMMA chain complicate considerably hinders the process kinetic. To go further on the understanding of the electrochemical oxidation of polymeric materials, we investigated the electro-oxidation of poly(ethylene glycol) (PEG) in a Proton Exchange Membrane (PEM) reactor. The system was initially studied using ethylene glycol on state-of-the-art electrodes. The anode formulation and morphology were optimized for its application to these organic macromolecules. The impact of temperature (30-80 °C), polymer concentration (1-20 g L-1) and molecular weight (200-4000 g mol-1) on the performance of the system was investigated. It was found that PEG can be electro-oxidized following two main routes involving weakly adsorbed or strongly chemisorbed species. Moreover, the production and purity of hydrogen in the cathode compartment was verified by an on-line mass spectrometer (Figure 1a), with a faradaic efficiency of 99.75%. The size of the macromolecules decreased after a chrono-amperometry experiment, as confirmed by steric exclusion chromatography (SEC) (Figure 1b), demonstrating the partial electro-oxidation of polymers containing C-O bonds in their main chain. The application of this concept for the production of hydrogen by electrochemical means seems promising, but further research in this field is necessary.

Context and purposePt/CeO2 is a promising catalyst for the low temperature water gas shift reaction (WGS). Moreover, it is “dynamic” since Pt can be dispersed during an oxidative treatment at moderate temperature leading to single atoms catalysts (SACs) while a reducing treatment triggers 3D particles formation. Starting from SACs, suitable redox treatments were previously shown to tailor nanoclusters more active for the low-temperature CO oxidation in the presence of water.In this work, the influence of different redox treatments on the WGS activity of Pt/CeO2 catalysts has been investigated depending on the Pt surface density as well as the doping by alkali cations. Relationships between physicochemical and catalytic properties have been established based on several complementary characterization methods including in situ/operando techniques.Material and methodsPt/CeO2 catalysts with different loadings were prepared by wet impregnation using Pt(NH3)4(NO3)2 as precursor and high surface area CeO2 as support, followed by calcination in air at 500 °C. A wet impregnation by alkali nitrates was further achieved on selected calcined samples for doping. The catalysts were characterized before, during and after the reaction by various techniques, including ICP-OES, XRF, BET, XRD, STEM-HAADF, H2 and CO-TPR, CO-DRIFT, and operando Raman and DRIFTS. The catalytic performances were measured using a fixed-bed reactor flowing a H2O/CO/Ar:32/8/60 mixture at atmospheric pressure and 235 °C.Main resultsThe Pt/CeO2 catalysts were shown to be predominantly SACs after calcination. Catalytic data revealed a quick ceria reduction under the reaction feed, while STEM images showed the formation of 3D Pt nanoparticles (NPs) of ca 1.5 nm after only a few minutes on stream. Interestingly, an optimal H2 productivity was observed after a few minutes likely due to intermediate active sites transiently formed. An optimal H2 productivity was also observed for a Pt coverage of 0.12 at/nm2 (figure 1A), revealing two different behaviors for high and low loadings. They are attributed to a balance between the Pt dispersion and the reducibility of ceria (figure 1B).Furthermore, different pretreatments were applied to tune the Pt NPs size. A reductive treatment at 500 °C improves the catalytic performances at low Pt loadings by strongly improving the surface ceria reducibility (figures 1B and C), while it decreases the catalytic activity at high loadings by Pt sintering. Various oxidative treatments were also performed to redisperse Pt particles after 1 h on stream. For low Pt loadings, the initial activity is recovered after an oxidative treatment at 230 °C, while this catalyst is strongly activated after an oxidative treatment at 500 °C (figure 1A).Alkali dopants increase the activity of the Pt/CeO2 catalysts with high Pt loadings, presumably by stabilizing ultradispersed Pt species and modifying the ceria reducibility. However, they strongly poison the catalysts at low Pt loadings.Major conclusionsBoth structural dynamics and ceria redox properties of Pt/CeO2 control its catalytic activity in WGS. These two parameters strongly depend on the Pt surface density and the presence of alkali dopants, allowing the use of redox treatments as a key strategy to (re-)activate the catalyst.

A novel method of catalysts synthesis has been studied for the past years where the ions of the active catalyst are initially introduced in an A-site deficient perovskite lattice under oxidizing conditions and later released as anchored nanoparticles (NPs) on the surface of the perovskite during a reduction step1. This so-called redox exsolution process has been largely investigated for Ni exsolved particles2. These Ni NPs present very specific interactions with their parent oxide compared to NPs externally dispersed onto the perovskite by conventional impregnation methods. For instance, due to their embedded structure within the perovskite supports, emergent NPs are more resilient to agglomeration and coking3, two main causes of catalysts deactivation, compared to similar particles made by alternative methods. Hence, the phenomenon of exsolution of metal NPs shows great potential for the development of advanced functional catalytic materials. However, emergent NPs are commonly exsolved from perovskites prepared by a solid-state method which includes a calcination step at high temperature, typically 1000°C. This results in very low surface areas of the perovskite support, lower than 5 m²/g. Here we report for the first time the Ni redox exsolution from a large specific surface area (SSA) perovskite (La0.52Sr0.28Ti0.94Ni0.06O3, denoted as LSTNi). The catalytic activity and stability of the emergent Ni NPs were compared with those of a Ni-impregnated perovskite (La0.52Sr0.28Ti0.8O3, denoted as LST) of similar SSA and Ni loading, using CO oxidation as a reaction probe.

The use of direct liquid fuel cells is acquiring increasing interest as an alternative to hydrogen fuel cells, given the low H2 volumetric energy density and difficulties linked to its storage, transport and handling. In particular, direct isopropanol fuel cells (DIFC) has two main competitive advantages: i) Isopropyl alcohol (IPA) electrooxidation reaction leads to negligible CO2 production at the anode, as opposed to the oxidation of methanol or ethanol, among others,1 and ii) the main oxidation product, i.e., acetone, is easily hydrogenated back to 2-propanol either catalytically or electrochemically. In this way, acetone becomes a promising hydrogen receptor to be coupled with liquid organic hydrogen carriers in a proper transfer hydrogenation system.2 However, DIFCs typically employ Pt-based anodes, which suffer from a strong metal deactivation due to adsorbed acetone. The use of binary catalysts like PtRu partially solves this problem,1,3 but a deep understanding of this particular deactivation phenomenon still lacks. In the present work, isopropanol electrooxidation reaction in acidic media has been studied on Pt/C and PtRu/C catalysts under different operation conditions to evaluate the electrocatalytic activity, selectivity and stability of these model electrodes and to determine the most appropriate conditions to avoid or mitigate the catalyst deactivation.

Biomass transformation to some valuable chemical products via photocatalytic or photoelectrocatalytic technologies

Les catalyseurs de métaux supportés sont largement utilisés dans l’industrie. Les nanoparticules (NPs) métalliques sont généralement dispersées sur le support par une méthode d’imprégnation. Une autre voie de synthèse a été récemment proposée dans laquelle le métal est initialement incorporé dans le réseau cristallographique de l’oxyde. Une étape de réduction (chimique ou électrochimique) permet de réduire ces cations qui migrent en surface pour former des NPs1. Ce processus d’ex-solution redox a été largement étudié pour des oxydes de structure pérovskite.2 Les NPs émergentes fortement ancrées en surface sont plus résistantes à l'agglomération et au cokage,3,4 deux principales causes de désactivation des catalyseurs et des électrocatalyseurs. Néanmoins, les études portent sur des pérovskites de faibles surfaces spécifiques. Nous avons préparé des titanates de lanthane dopées au Ni (La0.52Sr0.28Ti0.94Ni0.06O3 (LSTNi)) de surface spécifique supérieure à 20 m²/g par la méthode Pechini. L’impact de réductions chimiques sous H2 et électrochimiques sous H2O sur l’émergence de NPs de Ni et leurs propriétés catalytiques a été étudié en utilisant l'oxydation du CO comme réaction modèle. Nos résultats montrent que l’exsolution de NPs de Ni a lieu dès 400°C sous H2 pendant 2 h. L’activité catalytique des NPs émergées de Ni est à la fois supérieure et plus stable (Fig. 1) que celle de NPs imprégnées sur une pérovskite non dopée (Ni/LST, La0.65Sr0.35TiO3). Une couche de LSTNi a été déposée sur un électrolyte YSZ afin de déclencher l’ex-solution redox de Ni par voie électrochimique dans une cellule à 2 atmosphères. L’objectif visé est de comparer la méthode de réduction (chimique ou électrochimique) sur la nanostructure et les propriétés catalytiques des NPs de Ni émergées.

SSCI-VIDE+CARE+JJI:FDA:PVE:ACV:CGU; National audience; Biodiesel is a renewable, biodegradable, non-toxic, low-sulfur fuel, and its performance is quite similar to fossil fuel diesel, so it can be used as a clean and renewable energy alternative to fossil fuels. In the practical production process of biodiesel, around 0.1 ton of by-product glycerol will be generated followed by the fabrication of 1 ton of biodiesel. [1] A feasible way to avoid resource waste is to convert glycerol into more valuable chemical products, which can not only create good economic benefits but also cater to the global low-carbon and energy-saving environmental protection needs by avoiding direct burning of crude glycerol. [2] Photocatalysis is considered a green and energy-saving technology that utilizes light to generate charge carriers and active species to activate the target molecules. [3]In this study, , the performance of WO3-based catalysts for the selective photooxidation of glycerol towards glyceraldehyde was obtained. By comparing the activity of pure TiO2 (Anatase, Rutile, and P25) and pure WO3 (prepared by a simple hydrothermal method), it is found that: i) TiO2 catalysts allowed for a higher overall conversion of glycerol, where the selectivity to glyceraldehyde was limited by its further photooxidation, and ii) WO3 catalyst exhibits slower kinetics for glycerol oxidation but shows an outstanding selectivity (29%) and yield (13%) of glyceraldehyde. While the activity of TiO2 was attributed to electronic effects (better separation of photogenerated charge carriers), the high glyceraldehyde selectivity of WO3 was linked to its enhanced acidity, which selectively activates C-O bonds in glycerol, and facilitates the desorption of glyceraldehyde (avoiding its further photooxidation). Hence, a commercial WO3/TiO2 material (DTW5) was proven to combine the best features of both semiconductors, with high levels of glycerol conversion and selectivity (19%) to glyceraldehyde. This study opens a new field dealing with the development of advanced photocatalytic materials for an advanced valorization of glycerol into high added-value products. [1]C. Santibáñez, M.T. Varnero, M. Bustamante, Chil. J. Agric. Res. 71 (2011) 469–475.[2]M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina, Angew. Chemie - Int. Ed. 46 (2007) 4434–4440.[3]J. Payormhorm, R. Idem, Appl. Catal. A, Gen. 590 (2020) 117362.

SSCI-VIDE+CARE+NGO:PVE:ACV; International audience; Hydrogen is an essential industrial target area, not only because of its use as an energy carrier and practical employment in fuel cells but also for its role as a significant raw material of the chemical industry [1]. Today, the steam reforming of fossil fuels (primarily methane) is the most common and cost-effective H2 production process [2]. Notwithstanding its advantages, it requires additional units to separate H2 from the coproduced CO and CO2, and it actively contributes to greenhouse gas emissions [3,4]. Hydrogen can also be produced by electrolysis of water; this environmentally friendly process has taken force lately because it can be easily integrated to the electrical grid and use renewable energy sources (i.e. solar or wind) to produce pure H2 from water, producing only O2 as a by-product [5].However, the thermodynamic cell voltage to achieve the water electrolysis reaction is around 1.23 V at room temperature [6]. Consequently, different strategies have been proposed to electrolyze organic molecules instead of water at the anode of low-temperature electrolyzers to reduce the energy demand. Plastic wastes contain an abundant source of hydrogen and can be a promising renewable feedstock for electrolysis. Among the different plastics, poly(methyl methacrylate) (PMMA) is a widely used polymer in several applications. Even if different recycling methods are implemented, such as thermal and chemical processes, any other processes than the incineration for direct Energy Recovery is rather useful. The present study proposes a new route to valorize plastic wastes by producing H2 using electrolysis. Due to the complexity and the heterogeneity of real PMMA-based plastics, our strategy, as a first approach, was to investigate the electrolysis of methyl pivalate (MP) as a model molecule representative of the polymer since it contains similar chemical units. We studied the electrooxidation of MP in a Polymer Electrolyte Membrane-based (PEM) reactor. The electrooxidation process of MP shows an entirely different behavior than the electrolysis of water at similar conditions and higher activity at potentials lower than 1.23 V. In-situ gas analysis by mass spectrometry allowed us to confirm the relation between the generated current and the production of hydrogen in the cathodic side of the PEM arrangement [7].To go further, real PMMA (Mw~15000 g/mol) was electrooxidized in a 2-electrode liquid cell system at 70°C in a liquid acidic electrolyte (H2SO4 1 M). Using a dissolution strategy with a binary solvent (2-propanol/water), the PMMA electrooxidation proof-of-concept was validated on a commercial Pt/C electrode despite strong deactivation issues that became stronger at high polymer concentrations, as shown in Figure 1. This degradation of the performances could be attributed to the accumulation of polymer that blocks the electrode pores and/or a possible adsorption of intermediate species produced on the catalyst surface. However, the application of a potential of 1.4 V for few hours at 70°C can regenerate the electrochemical performances of the anode as demonstrated by ATR-FTIR experiments carried out on a model Pt/C anode. Our results demonstrate, for the first time, that plastic wastes such as PMMA can be electrooxidized at 70°C in an acidic media even if the composition and microstructure of the anode have to be tuned to improve the performance and the durability.

SSCI-VIDE+CARE+NGO:PVE:ACV; International audience; Hydrogen is an essential industrial target area, not only because of its use as an energy carrier and practical employment in fuel cells but also for its role as a significant raw material of the chemical industry [1]. Today, the steam reforming of fossil fuels (primarily methane) is the most common and cost-effective H2 production process [2]. Notwithstanding its advantages, it requires additional units to separate H2 from the coproduced CO and CO2, and it actively contributes to greenhouse gas emissions [3],[4]. Hydrogen can also be produced by electrolysis of water; this environmentally friendly process has taken force lately because it can be easily integrated to the electrical grid and use renewable energy sources (i.e. solar or wind) to produce pure H2 from water, producing only O2 as a by-product [5].However, the energy requirement correlated to the thermodynamic data shows a relative standard cell voltage of around 1.23 V to achieve the water electrolysis reaction at room temperature [6]. Consequently, different researchers have proposed to electrolyze organic molecules instead of water to reduce energy demand. Plastic wastes contain an abundant source of hydrogen and can be a promising renewable feedstock for electrolysis. Among the different plastics, poly(methyl methacrylate) (PMMA) is a widely used polymer in several applications [40]. Even if different recycling methods are implemented, such as thermal and chemical processes, any other processes than the incineration for direct Energy Recovery is rather useful. In this sense, the present study proposes a new route to valorize plastic wastes by producing H2 using electrolysis. Due to the complexity and the heterogeneity of real PMMA-based plastics, we decided, as a first approach, to investigate a Methyl pivalate (MP) as a model molecule, representative of the polymer containing similar chemical units, including atoms, bonds and functional groups (ester), as showed in Figure 1. We studied the electrooxidation of MP in a Polymer Electrolyte Membrane-based (PEM) reactor with an acid membrane (Nafion®) and commercial Pt/C electrodes between 50 and 80°C. A complete study of the operation conditions was carried out to enhance the production of H2.The electrooxidation process of MP shows an entirely different behaviour than the electrolysis of water at similar conditions and higher activity at potentials lower than 1.23 V. Experiences at different temperatures demonstrate that 80ºC is optimal for the electrolysis of MP. As showed in Figure 2, a critical oxidation step takes place at ~700-750 mV when cyclic voltammetry is performed with a second peak registered when the potential is decreasing. That phenomenon is attributed to an unfinished cleavage process of the MP molecule in the surface of the Pt/C anode. Typically, at the presented conditions, the only possible reaction is the electrolysis of the ester group to form pivalic acid and methanol, with a subsequent electrooxidation of the alcohol to produce H2 and CO2. In-situ gas analysis by mass spectrometry allowed us to confirm the relation between the generated current and the production of hydrogen in the cathodic side of the PEM arrangement. These series of results demonstrate the electrooxidation of MP a potentials lower than those required for the water electrolysis. To go further, real PMMA (Mw~15000 g/mol) was electrooxidized in a 2-electrode liquid cell system at 70°C. Using a dissolution strategy with a binary solvent (2-propanol/water), the PMMA electrooxidation proof-of-concept was validated on a commercial Pt/C electrode despite strong deactivation issues.

SSCI-VIDE+CARE+PVE:ACV; International audience; Ethylene oxide (EO) is nowadays a chemical intermediate of paramount importance. As one of the highest volume petrochemicals, it serves as a precursor for the further production of added value molecules, including plastics, polyester and ethylene glycol. EO is industrially produced by the partial oxidation (epoxidation) of ethylene with air (or oxygen) on Ag/α-Al2O3 catalysts at low reaction temperatures (around 220 oC) and high pressures (10-30 bar). Silver is the only one known active heterogeneous catalyst for the epoxidation of ethylene. The epoxidation is in competition with the combustion side reactions of both ethylene and EO, leading to the production of CO2 and H2O. The mechanism of the epoxidation and, in particular the nature of the involved oxygen species are under debate. We have designed by reactive magnetron sputtering a solid oxide electrochemical cell based on nanostructured Ag/Gadolinia-Doped Ceria (a well-known O2- conductor) catalyst. We found an unprecedent linear increase of the selectivity towards EO (Fig. 1) and of the ethylene conversion. These results demonstrate that EO can be electrocatalytically produced in a solid oxide electrochemical cell between 220 °C and 300 °C on a nanostructured Ag/GDC electrocatalyst prepared by reactive magnetron sputtering. Despite low values of Faradaic efficiencies, the EO selectivity and the ethylene conversion can be increased at 220 °C with the application of small positive currents (< 1 mA) that correspond to an energy consumption of around ~ 1 mW/cm². This proof-of-concept opens the way for a new environmentally-friendly route (without utilization of chlorinated hydrocarbons) for the epoxidation of ethylene in a solid oxide cell via direct electrooxidation of ethylene. These results also underline the key role of O2- species in the mechanism of ethylene epoxidation on Ag.

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+CARE+SFA:ABO:ACV:SGI:PVE; International audience; None

SSCI-VIDE+CARE+ACV:NGO:PVE; International audience; The main objective of this work is to develop a radically new scientific approach for the valorization of plastic wastes. The idea is to electrochemically transform plastic wastes into pure H2, the green energy vector for a sustainable world. Our main scientific breakthroughs deal with understanding and enhancing the kinetics of the electrochemical oxidation of model polymers in low temperature electrolyzers

SSCI-VIDE+CARE+ABO:ACV:PVE; International audience; The aim of this study is to unravel the mechanism of (noble metal oxide)/(active support) interactions for catalytic purposes. Hence, isotopic oxygen exchange (IOE) tests were performed on Iridium‐ and ruthenium‐based oxides supported on cerium oxide (CeO2), titanium oxide (TiO2), and yttria‐stabilized zirconia (YSZ). IOE tests demonstrated the metal oxide support involvement in the propane oxidation reaction, with YSZ‐based catalysts showing the highest exchange rate of oxygen, while CeO2 and TiO2‐based catalysts had a less diffusion of lattice oxygen in that order. This is related to the presence of extrinsic oxygen vacancies in the YSZ‐based catalysts and the reduction ability of the CeO2 and TiO2 supports. Despite the limitations on oxygen exchange in some of the noble/metal oxide catalysts, their catalytic performance was comparable to the ones that showed a high oxygen exchange. Therefore, active supports results in a higher engagement of oxygen from the support but not in a linear correlation with the catalytic performance of the metal/support.

SSCI-VIDE+CARE+PVE; International audience; Electrochemical Promotion of Catalysis (EPOC) or non-Faradaic electrochemical modification of catalytic activity (NEMCA) is a promising concept for boosting catalytic processes and advancing the frontiers of catalysis. This innovative field, discovered by the group of Professor C.G. Vayenas in the early 80s [1], aims to modify operando both the activity and the selectivity of catalysts, in a reversible and controlled manner. More than 80 different catalytic systems (total and partial oxidations, hydrogenations, dehydrogenations, isomerisations, and decompositions) have been electrochemically promoted on metal or metal oxide catalysts supported on different ionic conductors [2,3]. These include reaction systems of critical importance in diverse fields of chemical synthesis including the production of commodity and fine chemicals and in the abatement of automotive emissions. EPOC utilises solid electrolyte materials (ionically conducting ceramics) as catalytic carriers. Ions contained in these electrolytes are electrochemically supplied to the catalyst surface and act as promoting agents to modify the electronic properties of the catalyst in order to achieve optimal catalytic performance. Different types of ions such as O2-, Na+, H+, K+ have been successively used in the literature to boost catalytic properties of catalytic materials. It thus provides a unique means of varying promoter levels at the metal surface under reaction conditions by simply changing the potential of the catalyst film. Therefore, EPOC can be consid&ered as an electrically controlled catalyst-support interaction in which promoting ionic agents are accurately supplied onto the catalytic surface by electrical potential control.The main technological issue of EPOC is related with the use of continuous metallic coatings interfaced onto dense solid electrolyte supports. On account of that, the metallic dispersion of the catalyst-electrodes, and therefore their catalytic activity, is usually far lower than that of commercial dispersed catalysts. In addition, the thermal stability of continuous metallic coatings is rather low to the sintering phenomenon especially when using transition metals. This explains why most of the EPOC studies reported in the literature have been performed on Platinum Group Metals (Pt, Pd, Rh) and to a lesser extent on Ag, Ru and Ir. The utilization of pure precious metals catalytic layers is not economically reliable. Furthermore, the thermal stability of pure transition metals coatings deposited on dense solid electrolyte supports is too low to be realistically implemented for catalytic processes. Therefore, some research efforts are focused to achieve EPOC over catalytic dispersed nanoparticles. This plenary lecture will give an overview of recent advances in the quest of electropromoted nanoparticles including innovative architectures of catalyst-electrodes.

SSCI-VIDE+CARE+ACV:SGI:PVE; International audience; To this date it is well known that H2 is an excellent energy carrier, which is expected to play a key role in near-future energy systems. Water electrolysis has gained much attention lately, since it allows to produce pure H2 quick and conveniently. Its main drawback is related to its high electrical energy requirements, which makes the process economically unattractive . In this sense, the electrolysis of organic molecules (methanol, ethanol, bioethanol, etc.) allows to produce pure H2 with much lower power demands. Lignin is one of the most abundant bio-polymers in nature. Nowadays, about 50 million tons of lignin are produced annually as a waste stream of the Kraft pulping industry for cellulose production . In this study we propose, for the very first time in literature, to perform the direct electrolysis of lignin-based solutions in PEM reactors under continuous operation mode to produce pure H2.

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.

SSCI-VIDE+CARE+ABO:PVE; National audience; 1. Introduction Particulate Matter (PM) emission abatement for passenger Diesel vehicles has become more and more stringent over the past years. From 2009, Euro 5 standards have permitted to generalize Diesel Particle Filter (DPF) to reduce PM emissions. DPF proved to be an efficient way to trap soot particles in the exhaust, the main drawback being the necessity to regenerate the filter regularly as soot collection slowly obstructs the filter, increasing the pressure drop. Therefore, an efficient catalyst for the DPF regeneration at low temperature, using only oxygen as an oxidant, is strongly required. Our group has shown that Yttria-Stabilized Zirconia (YSZ), a well-known pure oxygen ionic conductor, can oxidize soot [1-3] with lattice oxygen active species with a concomitant gaseous oxygen replenishment into the lattice. This study aims to investigate the mechanism of soot oxidation over bare YSZ and silver-supported YSZ through labelling oxygen adsorption and exchange, CO2 adsorption and exchange as well as isotopic oxidation of soot. 2. Experimental A series of silver-impregnated YSZ catalysts was prepared by wet impregnation followed by calcination at 700°C. Catalysts displayed silver loading ranging from 0 to 7.5wt%. Samples were characterized by XRD, XPS and TEM. Performances toward soot oxidation were measured by running TPO (temperature-programmed oxidation) of a mixture of model soot (Printex U) and catalyst with various partial pressures of oxygen. Similar experiments were performed with labelled O2 (Temperature-programmed Isotopic exchange, TPIE). Isothermal oxygen exchange (IOE) experiments were also conducted with C16O2 over previously exchanged samples with labelled oxygen. 3. Results and discussionAg/YSZ catalysts display high thermal stability and maximal activity for soot oxidation for remarkably low loading of Ag (1 wt.%) thanks to the ability of silver to disperse into small metallic nanoparticles. The mobility of silver particles allows contact improvement between the catalyst and soot. Oxygen partial pressure was shown to impact performances; the activity drop when decreasing the oxygen partial pressure from 5 to 1% was found to be stronger in the presence of silver than over bare YSZ, thus indicating that silver plays a role into oxygen replenishment. As YSZ is a non-reducible oxide, soot oxidation must involve the integration of gaseous oxygen into the lattice to replace lattice oxygen species consumed to oxidize soot. This is most probably the rate-determining step of the overall combustion process. This replenishing of YSZ is promoted by Ag nanoparticles, as confirmed by TPIE. Their presence on YSZ strongly promotes the oxygen dissociative adsorption, as well as its integration into the YSZ lattice. CO2 exchange occurred at low temperatures and could be considered as an artefact when performing isotopic soot oxidation. This underlines that the oxygen mechanism via surface carbonation must be carefully analysed to clearly conclude the origin of the active oxygen species. Isothermal oxygen exchange experiments performed at 400°C with labelled oxygen on YSZ and Ag/YSZ in both tight and loose contact modes with the model soot clearly show that the largest amount of lattice oxygen is detected in the CO2 produced during the first 20 min of the soot combustion process in comparison with the CO2 route exchange. This indicates that YSZ bulk oxygen species are largely involved in soot oxidation. Figure 1. Mechanism for soot ignition over Ag/YSZ, oxidation of soot to CO and CO2 on YSZ (1) and in contact with Ag (2), O2 adsorption and dissociation over silver nanoparticles (3).4. ConclusionsIsotopic experiments proved that active oxygen species for soot oxidation originate from the YSZ lattice, despite the fact that gaseous CO2 exchange also occurs over the catalyst. Silver nanoparticles promote soot oxidation activity by activating the dissociative adsorption and lattice integration of gaseous oxygen. References 1. E. Obeid, L. Lizarraga, M.N. Tsampas, A. Cordier, A. Boréave, M.C. Steil, G. Blanchard, K. Pajot, P. Vernoux, Continuously regenerating Diesel Particulate Filters based on ionically conducting ceramics, J. Catal. 309 (2014) 87–96.2. E. Obeid, M.N. Tsampas, S. Jonet, A. Boréave, L. Burel, M.C. Steil, G. Blanchard, K. Pajot, P. Vernoux, Isothermal catalytic oxidation of diesel soot on Yttria-stabilized Zirconia, Solid State Ionics, 262 (2014) 253–256.3. A. Serve, A. Boreave, B. Cartoixa, K. Pajot, P. Vernoux, Synergy between Ag nanoparticles and yttria-stabilized zirconia for soot combustion, Appl. Catal. B Environ. 242 (2019) 140–149.

SSCI-VIDE+CARE+ACV:SGI:PVE; International audience; In this study we have demonstrated, for the first time, the possibility to advance a step forward for the development of a sustainable technology (electrolysis) towards the valorization of biomass-derived resources (lignin waste) for the production of pure H2.

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.

MICROSCOPIE+CARE:ECI2D+MAO:SLO:PVE; International audience; The tailoring of exhaust gas catalysts is crucial to improve the air quality. Upgrades in the efficiency of the combustion process and low energy losses in the engine lead to low temperature in the exhaust line. The challenge to comply with the incoming severe legislations is to develop active catalytic converters in urban mode, typically at temperatures from 150 °C, including cold-start phases. Furthermore, design of new catalysts has to take into account scarcity of sensitive elements especially noble metals. Decreasing the metal loading over an oxide support can stabilize new types of catalytic sites (single atoms, subnanometric clusters) [1] which have to be more efficient as their concentration is limited. The interactions between such nanometric sites with the support play a key role in their thermodynamic stability, electronic and catalytic properties. In addition, the interface between noble metal nanoparticles, such as Pt and Pd, with ceria-based oxides can be tuned by exposing the catalysts to suitable redox conditionings [2-4]. This dynamic nature of the metal/ceria interface can be exploited to rationally enhance the low-temperature oxidation activity. This lecture will summarize recent advances in the concept of dynamic catalysts achieved by our group in collaboration with the Institut de Chimie de la Matière Condensée at Bordeaux and the Karlsruhe Institute of Technology. The presentation will be focus on Pt and Pd-based catalysts supported on ceria oxides for the oxidation of CO and hydrocarbons.

SSCI-VIDE+CARE+MCX:IKL:PVE:ACV; International audience; Catalytic reactions may be promoted in a controlled and reversible manner in electrochemical devices via electrochemical promotion of catalysis (EPOC) [1]. This phenomenon is based on the modification of the local electronic density of the surface of a catalyst coated on a dense electrolyte via the supply of O2- anion. The latter impact the catalytic performances of the catalyst behaving as electronic promoters. So far, the main technological issue of EPOC is related to the use of continuous metallic coatings interfaced on dense solid electrolyte supports. On account of that, the metallic dispersion of the catalyst/electrodes, and therefore their catalytic activity, are usually far lower than that of commercially available dispersed catalysts. Hence, one of the main challenges of the EPOC phenomenon is to combine dispersed catalysts at the nanometric scale with the concept of electrochemical activation via EPOC. In this sense, within the last decade, a powerful phenomena known as exsolution has been identified as a versatile tool allowing a control of the reactivity and durability of metallic particle [2]. Upon the use of ABO3 perovskite materials, certain metals can be inserted within the lattice on the B sites under oxidizing conditions. Upon reductive thermal treatment, the aforementioned metal exsolves, allowing the in situ growth of metallic nanoparticles. Fine tuning of the experimental condition allows the formation of well anchored and well distributed nanoparticles. The non-stoichiometry of the perovskite (i.e. A site deficiency) appears as one of the key parameter driving the exsolution of metal cations to its surface [2]. Recent progress have shown that the exsolution process can be driven electrochemically in fuel cell type devices.The aim of this work is to prove, for the very first time, that stable and well dispersed metallic nanoparticles on the surface of a perovskite may be obtained via exsolution and their activity could be enhanced via EPOC. The perovskite chosen was a A site deficient lanthanum calcium titanate (LCT) doped with 6 % of nickel on the B site (i.e. La0.43Ca0.37Ni0.06Ti0.94O3-δ; LCNT6). It was prepared via a citrate sol-gel synthesis [3] with a calcination temperature of 1200 °C leading to a specific surface area of 7 m2·g-1. A reduction was then performed in 5% H2 (i.e. 900 °C, 2 h) in order to exsolve Ni from LCT lattice. The material was then tested for CO oxidation allowing to probe its catalytic performance (see Figure 1). One can observe that the reductive treatment clearly enhanced the catalytic activity of LCNT6. Moreover, in order to study the stability of the Ni nanoparticles formed via exsolution, a hydrothermal treatment was applied (i.e. 900 °C, 24 h, 10% H2O) followed by a subsequent reduction (i.e. 900 °C, 2 h, 5% H2). As observed in Figure 1, the activity of LCNT6 was not affected by this treatment suggesting the good thermal stability of Ni particles regarding aggregation. To further study the stability of the exsolved nanoparticles aging in presence of water and oxygen was performed (i.e. 900 °C, 24 h, 10% H2O, 20% O2) followed by a reduction (i.e. 900 °C, 2 h, 5% H2). The performance of LCNT6 is not affected either by a hydrothermal treatment in presence of oxygen which proves Ni nanoparticles formed via exsolution to possess very good stability properties. Following the successful formation of stable Ni particles via exsolution on the surface of LCT, electrochemical promotion of catalysis was investigated on this material for CO oxidation. [1] P. Vernoux et al., Chem. Rev., 113, 8192 (2013)[2] D. Neagu et al., Nature Chemistry 5, 916 (2013)[3] N.K.Monteiro et al., International Journal of Hydrogen Energy, 37, 9816, (2012)

MICROSCOPIE+CARE+TCV:TTG:IKL:ABO:LBU:FGA:ACV:PVE; International audience; Electrochemical Promotion of Catalysis (EPOC) is an innovative concept for boosting catalytic processes in a reversible and controlled manner [1]. The EPOC phenomenon takes place in fuel-cell type reactors where the catalytic coating is an electrode supported on a dense ionically conducting ceramic material (solid electrolyte). Ions, such as K+, contained in these solid oxide electrolytes are electrochemically supplied to the catalyst surface, changing its local electronic density. This way, the ions supplied behave as electronic promoters, modifying the activity and the selectivity of the catalyst. We used EPOC for designing new environmentally-friendly catalysts for the epoxidation of ethylene in order to produce ethylene oxide at atmospheric pressure with high selectivity to ethylene oxide (EO) without the need for chlorinated hydrocarbons in the gas feed. We have prepared Ag-based composite electrodes as Ag is the most efficient metal for this reaction. Composite electrodes were prepared from a mixture between a Ag commercial paste and either a pure oxygen ionic conductor, i.e. Yttria-Stabilized-Zirconia (YSZ) or a Mixed Ionic and Electronic Conductor (MIEC), i.e. LSCF (La0.6Sr0.4Co0.2Fe0.8O3). These composites electrodes were deposited either on YSZ or on K+ conducting β-Al2O3 membranes. The impact of current applications on the ethylene oxide selectivity was carried out at 300°C while the electrochemical properties of the different Ag-based composite electrodes were investigated by cyclic voltammetry. In addition, TEM (JEOL 2010) and Environmental SEM (FEI QUANTA 650 FEG) were implemented to characterize the nanostructure of the electrodes including in-situ observations at 300°C in air. Composites electrodes were prepared by mixing 75 wt.% of a commercial Ag paste (Metalon® HPS-FG32) with 25 wt.% of a powder of YSZ (TOSOH) or LSCF prepared with the Pechini method. These mixtures were deposited on YSZ or β-Al2O3 (Ionotec) dense membranes and calcined at 600°C for 2 h. The as-deposited morphology of these layers shows large micrometric Ag agglomerates mixed with nanometric grains of YSZ or LSCF. A period of activation of around 6 h on stream (C2H4/O2: 3.8%/1.1%) at 300°C was necessary to reach a steady-state activity with an EO selectivity at around 12% for an ethylene conversion of 4%. This activation process was attributed to the transfer of Ag from large Ag agglomerates to the conducting oxide surface in the form of 5-10 nm diameter Ag nanoparticles (Figure 1) due to the high evaporation rate of AgOx at 300°C. This evaporation process was in-situ observed in air at 300°C with the ESEM. Therefore, the activation process on stream at 300°C leads to highly dispersed Ag-based composite electrodes containing Ag NPs supported on YSZ or LSCF. The impact of potential and current applications on the EO selectivity was investigated at 300°C according to the nature of the solid electrolyte (O2- and K+ conductors) and the conducting oxide in the composite (YSZ and LSCF).

SSCI-VIDE+CARE+PVE; International audience; None

MICROSCOPIE+CARE+IKL:TCV:ABO:LBU:FGA:LRE:ACV:PVE; International audience; Catalytic combustion as a process used for removal of hydrocarbons from automotive gas exhausts or for energy production has been widely implemented on supported PGM (Platinum Group Metals) based catalysts1. Since PGMs are very costly and rare, there is a strong need for an equally effective and less expensive catalyst. The electrochemical promotion of catalysis (EPOC), is a promising concept to in-operando boost catalytic processes in a reversible and controlled manner2. The aim of this study was to develop Ag-based electrochemical catalysts for low temperature propylene deep oxidation. EPOC of propylene combustion has been carried out in the literature but mainly on Pt catalytic films1,3, while this phenomenon was attributed to the modification in the propylene chemisorption3.Nanostructured electrochemical catalysts were prepared by screen-printing and reactive Physical Vapor Deposition (PVD) method. Thickness and porosity of Ag coatings were modified by changing the deposition parameters (duration and pressure for PVD, nature of the ink and calcination temperature for screen-printing) to optimize the catalytic properties. Catalytic and electrocatalytic tests have been carried out in a quartz reactor1 which operated under continuous flowing conditions at atmospheric pressure. The catalytic activity was monitored in a temperature range of 100 to 400oC under lean-burn conditions, as encountered in Diesel exhausts. The most active Ag films were also evaluated under closed circuit conditions (± 2V) in order to measure the effect of polarization between the Ag working electrode and an Au reference electrode. Both electrodes were exposed to the same atmosphere in a single chamber configuration.Values of Faradaic efficiencies in the range of 300 were obtained while the conversion could be tailored from 14 to 21% (Fig. 1). Negative current applications lead to the decrease of the CO2 production while positive current application corresponds to a pronounced increase of the catalytic performance. Upon positive current applications, the rate enhancement ratio increases with the intensity of the current. This indicates that the coverage of promoting ionic species (Oδ-) increases with the current, then producing more weakly bonded oxygen species coming from the gas phase4.This study reports, for the first time, that the catalytic activity for propylene of Ag coatings deposited onto YSZ can be tailored by current applications in a non-Faradaic manner. The predominant impact of current applications is to modify the reactivity of oxygen present on the Ag surface. Positive current applications increase the propylene conversion by producing more reactive oxygen species. This beneficial effect is more pronounced in an oxidizing atmosphere, where the oxygen coverage on Ag is high. This demonstrates that EPOC can enhance catalytic properties of Ag coatings for the abatement of propylene in air.References 1.P. Vernoux et al., J. Catal., 208 (2002) 412-421.2.C.G. Vayenas, Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion, and Metal-Support Interactions, Springer, 2001.3.A. Kaloyannis et al., J. Catal., 182 (1999) 37-47.4.I. Kalaitzidou et al., Materials Today: Proceedings, 5, 27345 (2018).Acknowledgments: This study was performed in the “EPOX” project, funded by the French National Research Agency (ANR), ANR-2015-CE07-0026.

MICROSCOPIE+CARE+PVE:MAO; International audience; Environmental transmission electron microscopy (ETEM) equipped with an aberration corrector was used to get further insights into the oxidation soot on ceria-zirconia. In-situ ETEM observations in the presence of a few mbar of oxygen have shown that soot in intimate contact with the catalyst crystallites, achieved by a high-energy milling, can be oxidized at room temperature. This study confirms the importance of the soot/catalyst interface at nanoscale in the soot oxidation mechanism.

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.

SSCI-VIDE+CARE+CGU:MHM:PVE; International audience; Several studies have shown that volatile organic compounds (VOCs) can be concentrated in the car, enclosed and confined at rates higher than those of outdoor air [1]. Thus, the air quality is almost always less good inside and is degraded according to external parameters, ex. confined areas of traffic (eg tunnels) [2] or depending on the season (increase in VOC by 40% during summer, due to high temperatures). The presence of these VOCs in vehicle cabin air is responsible for allergies, respiratory problems, skin problems. As people spend a lot of their time in their vehicle [3], for example, in France, 73% of active population (18 million people) use their vehicles every day to go to work and spends an average of 78 minutes per day that is 3 years and 4 months of their life! [4], it is essential to develop an efficient device to remove them. Indeed, most of the actual depollution systems are based on adsorption of these compounds to store them.The QAIcar project aims to develop an air handling equipment dedicated to the automotive interior allowing to destroy microorganisms and VOCs.The project includes 3 innovations:- the coupling of catalysis at room temperature with photocatalysis- the development of a bactericidal luminous textile which will serve support for the coupling of catalyst and photocatalyst.- the concept of a compact reactor integrating the active luminous textile into a multilayer.This project brings together three academic laboratories, IRCELYON, CIRI and LMFA, a small and medium-sized enterprise, Brochier technologies, a mid-size companies, EFI Lighting who is the project leader and two big groups, St; Gobain CREE and the automotive manufacturer, PSA Group.In the poster will be describe the existing locks motivating the project, the objectives, the consortium and the structuring of the project as well as the first results[1] Delaunay C., Goupil G., Ravelomanantsoa H., Person A., Mazoué S., Morawski F., , Pollution atmosphérique 2012 ; 215 : 247 – 258[2] De Pas A., Boissavy-Vineau M., Bull. Epidémiol. Hebd. 2013 ; (1-2) : 17[3] D. Müller, D. Klingelhöfer, S. Uibel, D. A. Groneberg, (2011) J. Occup. Med. Toxicol, 6, 1701-1709[4] Enquête globale transport, STIF, janvier 2013 ; http://www.lievreoutortue.com/dans-votre-vie-combien-de-temps-passerez-vous-dans-votre-voiture/

MICROSCOPIE+CARE+ACV:GBH:IKL:MAO:PVE; International audience; In this study we developed novel materials based on Ni supported on Ce0.8Gd0.2O0.2GDC), for H2 production via methane reforming, by the Weak Acid Resin (WAR) process. This procedure allows to prepare NiO/GDC materials from ion exchange resin templates, then calcined in air to give the oxide material. Moreover, the surface area of these materials was enhanced by NiO partial dissolution in aqueous-acid solution. The whole procedure led to catalysts with unique properties compared to other materials reported in literature, i.e., high metal loadings (≥ 10 %), small Ni nanoparticles (< 10 nm), and high specific surface areas (> 70 m2/g).

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.

MICROSCOPIE+CARE+TCV:IKL:ABO:LBU:FGA:LRE:ACV:PVE; National audience; Des tests catalytiques et electrocatalytiques ont été menés sur des membranes denses conductrices ionique pour la combustion du propène en utilisant une couche catalytique d'argent synthétysée via PVD ou sérigraphie déposée sur une membrane dense de Zircone stabilisée avec 8% d'yttrium (YSZ), un conducteur ionique de O2-. Une adsorption compétitive entre le propène et l'oxygène a été observée à 300°C. Les performances catalyques des films d'argents ont pu être modifiées via une polarisation et ce, de manière non-faradique (effet EPOC) à 300°C. L'impact de la polarisation depend principalement du taux de recouvrement du propène sur l'argent : pour des taux de recouvrement faible comme dans des conditions d'oxydation, des effets de promotions ont été observés lors de polarisation positive alors que pour un fort taux de recouvrement, obtenu dans des conditions stoechiomètrique, seulement des effets d'inhibition ont pu être observé lors de polarisations négatives.

MICROSCOPIE+CARE+ACV:IKL:GBH:PVE:MAO; National audience; In this study we developed novel materials based on Ni supported on Ce0.8Gd0.2O1.9 (GDC), for H2 production via methane reforming, by the Weak Acid Resin (WAR) process. This procedure allows to prepare NiO/GDC materials from ion exchange resin templates, then calcined in air to give the oxide material. Moreover, the surface area of these materials was enhanced by NiO partial dissolution in aqueous-acid solution. The whole procedure led to catalysts with unique properties compared to other materials reported in literature, i.e., high metal loadings (≥ 10 %), small Ni nanoparticles (< 10 nm), and high specific surface areas (> 70 m2/g). Keywords: H2 production catalysts; nano-dispersed materials; NiO/GDC

SSCI-VIDE+CARE:ECI2D+GFE:SLO:PVE; National audience; Depuis plusieurs années, les normes européennes des émissions de NOx des véhicules diesel ne cessent de se renforcer. Parmi les solutions développées par les équipementiers, le procédé NOxTrap consiste à stocker et réduire les NOx au cours de cycles redox entre un mélange gazeux pauvre (échappement diesel) et riche en hydrocarbures. Les catalyseurs Pt/CeO2 servant à oxyder les imbrulés (CO, hydrocarbures) doivent être adaptés à l’application de ces cycles. Nous avons récemment montré la nature dynamique des nanoparticules (NP) de Pt sur l'oxyde de cérium lors de séquences réductrices/oxydantes à des températures inférieures à 500 °C. En outre, les impulsions pauvres/riches peuvent être utilisées pour contrôler la formation de Pt et améliorer leur activité catalytique pour l'oxydation de CO. Dans ce travail, les cycles redox sont simulés en alternant des traitements sous 10%H2 et 20%O2 à différentes températures. Parmi différentes techniques de caractérisation utilisées in situ, la spectroscopie Raman s’est avérée être clé pour mieux comprendre les évolutions structurales des catalyseurs Pt/CeO2 au cours de ces cycles redox. En particulier, la cartographie Raman in situ a permis de suivre la distribution des particules PtOx à l’échelle micrométrique. Cette méthodologie appliquée pour la première fois à l’étude de catalyseurs hétérogènes permet d’obtenir à la fois une information spatiale (Figure 1A) et statistique (Figure 1B) sur un paramètre spectroscopique donné. Il a ainsi été montré que les processus de dispersion et formation de particules s’opèrent à l’échelle micrométrique. De plus, l’évolution des bandes correspondant aux clusters PtOx (690 cm-1), des espèces oxygène peroxo (830 cm-1), de la bande de diffusion Raman électronique des cations Ce3+ (2100 cm-1) ont permis de mettre en évidence la stabilisation d’un état d’oxydation intermédiaire du Pt, probablement Pt2+, l’absence de cations Ce3+ et l’apparition d’espèces peroxo en surface de la cérine au cours de cycles redox. Cette stabilisation permettrait d’augmenter fortement l’activité oxydante des catalyseurs Pt/CeO2.RemerciementsLes auteurs remercient l‘Agence Nationale de la Recherche’ (ANR) pour le financement du projet ORCA (ANR-14-CE22-0011-02).Références1.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, 13078–13082.2.M. Daniel, S. Loridant, J. Raman Spectrosc. 2012, 43, 1312–1319.

SSCI-VIDE+CARE+ABO:PVE; International audience; La régulation des émissions particulaires se fait de plus en plus restrictive à la sortie des pots d’échappement des véhicules. Cela a conduit naturellement les constructeurs automobiles à mettre en place des systèmes de régulation de ces émissions. Le filtre à particules (FAP) est l’un de ces systèmes. Il est capable d’avoir une efficacité de filtration moyenne supérieure à 99% en prenant en considération tant la masse particulaire que le nombre de ces particules émises. La filtration est assurée par lit de suie. Lorsque celui-ci est complétement détruit lors des phases de régénération, le FAP filtre moins bien pendant quelques minutes, temps nécessaire pour reformer le lit de suie. On sait aujourd’hui qu’outre les motorisations Diesel, les motorisations à injection directe d’essence (IDE) sont aussi émettrices de particules. Non équipés de filtres, des tests sur banc moteur ont montré que ces moteurs émettaient une concentration élevée de particules, dans des concentrations de 10 à 1000 fois supérieures à celle des véhicules Diésel équipés de FAP. Ces dernières informations conduisent les constructeurs à équiper leurs véhicules IDE de filtres à particules essence (GPF pour Gasoline Particulate Filter) depuis la norme Euro 6c entrée en vigueur 2017 pour les nouveaux modèles. Nous avons étudié la possibilité de transposer la technologie FAP Diesel aux motorisations IDE. Sur un banc moteur, un GPF commercial a été installé sur une ligne d’échappement d’un moteur IDE Euro 5. Des expériences ont été menées afin de tester son efficacité sur la réduction des émissions particulaires. Nous présenterons le résultat de l’analyse des particules pour 3 points de fonctionnement du moteur en termes de nombre, masse, taille et nature chimique en 3 points de la ligne d’échappement : directement en sortie du moteur, après le catalyseur 3 voies et en aval du GPF.

International audience

SSCI-VIDE+CARE+PVE; International audience; Electrochemical Promotion of Catalysis (EPOC), also called Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA), is a promising concept for boosting catalytic processes and advancing the frontiers of catalysis [1]. This innovative field aims to modify in-operando both the activity and the selectivity of catalysts, in a reversible and controlled manner. EPOC utilizes solid electrolyte materials (ionically conducting ceramics) as catalytic carriers. Ions contained in these electrolytes are electrochemically supplied to the catalyst surface and act as promoting agents to modify the catalyst electronic properties in order to achieve optimal catalytic performance. This lecture will give an overview of recent advances of EPOC for energy conversion.[1] P. Vernoux, L. Lizarraga, M.N. Tsampas, F.M. Sapountzi, A. De Lucas-Consuegra, J.L. Valverde, S. Souentie, C.G. Vayenas, D. Tsiplakides, S. Balomenou, E.A. Baranova, Chem. Rev. 113 (2013) 8192.

SSCI-VIDE+CARE+MHM:PVE:CGU; International audience; The photocatalytic process is an efficient method to remove chemical and microbiological pollutants from indoor air in automotive cabin. In the present work, luminous textile was used at first as light source in the photocatalytic degradation of a mixture of pollutants and compared to classical UV lamp. Then, it was used both as light source and a (photo)catalytic support. In this case, the durability and the deposition quality have been optimized in order to preserve good photocatalytic efficiency. This innovative textile combining light source with photocatalyst has advantage of allowing the development of compact reactor with considerable gain of energy.

SSCI-VIDE+CARE:ING+MBH:FRM:CGU:PVE; International audience; 1. ScopeThe presence of Volatile Organic Compounds (VOCs) in indoor air is a major health issue. The vehicle cabin air is also affected by this problem as being the first mode of transportation [1]. Most of the current depollution systems are based on trapping using adsorption methods, while photocatalytic processes offer the potential to fully and continuously degrade VOCs. n-pentane and its derivatives are present in vehicle cabins [2], and to the best of our knowledge, the photocatalytic-oxidation of this compound has been scarcely studied [3-4]. This study deals with the photocatalytic degradation of n-pentane using a TiO2 DEGUSSA® P25 powder5. The impact of pollutant concentration (17-425 ppmv), relative humidity (r.h.) (0-90%), irradiance power at 365 nm (0.05-2.7 mW/cm²) and oxygen partial pressure (0.02-20%) on the degradation kinetic of n-pentane was investigated at room temperature. Operando DRIFTS experiments were performed under 1200 ppmv of n-pentane and 3.5% O2 in He to study the surface species formed on the photocatalyst and their evolution under UV irradiation. 2. Results and discussionResults show that the n-pentane degradation rate decreases with the relative humidity level, and linearly increases with the irradiance power and the VOC concentration. At 120 mL/min, r.h.=0%, 20% O2 and under an irradiance power of 2.7 mW/cm² at 365 nm, a degradation rate of 0.05 µmol/min is obtained. In addition, the presence of formates surface species under irradiation has been evidenced by DRIFT experiments [6-7]. 3. ConclusionsThis preliminary study has shown the impact of several parameters in the kinetic of degradation of n-pentane on titanium dioxide. Furthermore, this study highlighted the presence of formates surface species by surface investigation, during the photocatalytic degradation of n-pentane. These results give new insights in the understanding of the VOC photocatalytic degradation mechanism for improving depollution system in vehicle cabins.References 1. D. Müller, D. Klingelhöfer, S. Uibel, D. A. Groneberg, J. Occup. Med. Toxicol, 2011, 6, 1-7.2. J. Faber, K. Brodzik, A. Golda-Kopek, D. Lomankiewicz, Pol. J. Environ. Stud., 2013, 22, 1701-1709.3. N. Djechri, M. Formenti, F. Juillet, S.J. Teichner, Faraday Discuss. Chem. Soc., 1974, 58, 185-1934. A. K. Boulamanti, C. J. Philippopoulos, Atmos. Environ, 2009, 43, 3168–31745. M. Bouhatmi, F. Dappozze, C. Guillard, P. Vernoux, J. Earth Sci. Geotech. Eng., 2017, 7, 83-88. 6. G. Ya. Popova, T. V. Andrushkevich, Yu. A. Chesalov, E. S. Stoyanov, Kinet. Catal, 2000, 41, 885-891.7. G. Busca, J. Lamotte, J-C. Lavalley, V. Lorenzelli, J. Am. Chem. Soc. 1987, 109, 5197-5202.

SSCI-VIDE+CARE+PVE; International audience; Materials for car exhaust treatment

SSCI-VIDE+CARE+PVE; International audience; Materials for car exhaust treatment

SSCI-VIDE+CARE+PVE; International audience; None

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+CARE+IKL:SNS:PVE; International audience; Studies of CH4 oxidation are of special interest due to the difficulty in activating this particular hydrocarbon,to the demand of an active catalyst at low temperatures (T50 at 300oC) as well as due to possible deactivation of the catalyst upon exposure at higher temperatures. To address these issues, we have used Electrochemical Promotion of Catalysis (EPOC) which was discovered in the early 80's and has been studied for more than 100 catalytic systems. EPOC allows the controlled enhancement of the catalytic activity by potential or small current application between a catalyst (working electrode) supported on a solid electrolyte and an auxiliary electrode. In this study, the use of Pd nanoparticles (2-4 nm) as well as the use of nanodispersed Pd/Co3O4 and Pd/MnO2 catalysts deposited on O2- conductors (YSZ and CGO) is described. The aim is to demonstrate the feasibility of EPOC with nanodispersed catalysts and to enhance the reaction rate at temperatures lower than those that have been observed in previous studies.

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

SSCI-VIDE+CARE+DLG:PVE; International audience; The effect of a pretreatment step (reductive or oxidative) on the catalytic performance of Rh supported on ceria catalysts was evaluated for the oxidation of propane under stoichiometric conditions. Two different oxides were used (gadolinium doped ceria (GDC) and ceria zirconia (CZ)). The GDC support better stabilized Rh under the operating conditions used avoiding a strong deactivation of the catalysts after one hour on stream at 500 ºC. The shift of temperature for a conversion of 50 % (ΔTX=50) was of 30 ºC compared to 70 ºC suffered by the sample based on the CZ support. This fact is attributed to the formation of a mixed phase between Ceria and Rh as observed by TPR measurements and further investigated by XPS which stabilizes metallic nanoparticles. The behavior of the catalyst was evaluated under cyclic oxidation and reductive atmospheres. Finally, O218 experiments were carried out in order to get further information about the type of oxygen species involved in the reaction.1. Scope Catalytic oxidation of hydrocarbons is one of the most efficient air pollution control technologies for the purification of exhaust gas pollutants from intern combustion engines. Platinum group metals (PGMs) are regarded as the most efficient due to high activity and thermal stability. However, the content of PGMs has to be optimized due to their high cost. In automotive exhaust control, low amounts of Pd, Pt and/or Rh are used washcoated on an alumina/ceria zirconia support. Rhodium is a catalytically active key component of the three-way catalyst (TWC) for the effective conversion of CO, hydrocarbons and NOx1. The activity of the deposited noble metal is strongly influenced by their interactions with the support, especially those given on ceria based materials. Another key aspect is the oxidation state of the noble metal. In this regard, the transient and fluctuating conditions at which engines operate, including high oxygen concentrations, highly affect the state and subsequently, the final performance of the active phase. In this regard, in a previous work2, it was studied how the oxidation state of Pd supported on gadolinium doped ceria (GDC) or ceria zirconia (Zr) changed in the course of the stoichiometric propane oxidation reaction, affecting their catalytic activity. Furthermore, it was demonstrated via “in –situ” environmental TEM and XPS, that the metal support interactions (SMSI) played an important role and the GDC support better stabilize the Pd nanoparticles via the formation of a mixed Pd-ceria phase (surface interaction phase, PdxCeO2-δ). Moreover, the activity of the catalysts was fully recovered after a reduction treatment under hydrogen and associated to redispersion of Pd nanoparticles. Thus, it is crucial for the design of efficient catalysts to understand and control these phenomena, so that the activity of TWCs can be tuned depending on the reaction environment which would suppose an invaluable tool for optimizing their behavior and reduce the PGMs loading. In this regard, in this study we have evaluated the behavior of rhodium nanoparticles deposited on two ceria based materials, GDC (a mixed ionic conductor support) and ceria zirconia (a reference TWC support). The behavior of the catalysts was tested for the propane oxidation reaction under stoichiometric conditions and evaluated under different pretreatment conditions (oxidant and reductive). The influence of such pretreatments was evaluated by different techniques like XPS, TEM, TPR, TPD and O218. The authors certify that this is an on-going work and the results have not been published yet. 2. Results and discussionPowdered catalysts were prepared by dispersing Rh nanoparticles (1 wt. %) on a GDC (Rh_GDC) (Ce0.8Gd0.2O2) and a CZ (Rh_CZ) (Ce0.62Zr0.38O2) powder using incipient wetness impregnation. C3H8 catalytic combustion was evaluated under stoichiometric conditions (Figure 1) Prior to catalytic measurements, the samples were reduced under pure H2 (500 ºC, 1 hour). 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. Figure 1 depicts the light-off curves of the Rh_GDC and Rh_CZ catalysts. It can be observed that during the first cycle (after reduction), the performance of both catalysts is similar, reaching almost 100 % of conversion at 500 ºC. On the other hand, during the second cycle (after one hour on stream), the performance of both catalysts decays. The Rh_GDC catalyst is more stable than the Rh_CZ one. By taking into account the shift in temperature obtained at a conversion level of 50 % (ΔTX=50), the decay of the Rh_CZ catalyst is of 70 ºC, whereas the one for the Rh_GDC is of only 30 ºC. Similar results were observed for Pd nanoparticles supported over the same ceria based materials2. The low deactivation of the GDC catalyst is attributed to a higher interaction between the metal active site and the ceria support. Figure 1.b shows the temperature programmed reduction profiles (TPR) and the hydrogen consumption of the catalysts used in this study. It can be observed that both catalysts show two strong consumption of H2 at approximately 80 and 225 ºC and a wider peak at higher temperatures (≈ 670 ºC). The first peak (P1) it is associated to the reduction of RhO nanoparticles finely dispersed on the surface of the catalyst. The second peak (P2) is associated to the reduction of Rh nanoparticles in a strong interaction with the support. Finally, the third peak (P3) is associated to the reduction of the ceria support. It can be observed that the H2 consumption of Rh_CZ is higher at low temperatures (P1), whereas for the Rh_GDC there is greater amount of particles in close interaction with the support. This fact explains the higher stability of the GDC based catalysts, since the Rh nanoparticles are found anchored to the ceria support which stabilizes them under different atmospheres. Likewise, the similar performance of the Rh_GDC catalyst in the fresh state (first cycle), in spite of having half of the Rh available on the surface (P1), might be due to a better transfer of lattice O2 due to a better interaction of Rh with the GDC support. This fact is being further studied by O218 experiments in order to determine the nature of the oxygen species involved in the oxidation process. Furthermore, further insights on the different states of Rh, ceria and oxygen species under different pretreatment conditions will be assessed by XPS measurements. 3. ConclusionsThe catalytic activity of TWCs can be greatly promoted by the reduction of the metallic active phase. However, the deactivation of the catalyst takes place after its oxidation. This deactivation strongly depends on the metal/support interactions, being also reversible. The use of a mixed ionic conductor support (GDC) improved the resistance to deactivation of the catalyst. Hence, these results can contribute to the optimization design of TWCs and adapt its behavior to the transient conditions they suffer under real operation.

SSCI-VIDE+CARE+TTG:GPE:PVE; International audience; None

SSCI-VIDE+CARE+ACV:PVE; International audience; None

SSCI-VIDE+CARE:ING+MBH:FRM:CGU:PVE; National audience; De nos jours, la présence de Composés Organiques Volatils (COVs) dans l’air intérieur est un problème de santé majeur. Ils sont notamment à l’origine de nombreuses pathologies respiratoires, allergiques, dermatologiques…etc. L’habitacle automobile est sujet à cette pollution, notamment en France où l’automobile représente le 1er moyen de déplacement [1]. Plusieurs systèmes de dépollution, basés sur des méthodes d’adsorption, existent sur le marché, mais ne permettent qu’une simple rétention des COVs en surface. A l’inverse, la photocatalyse permet leur dégradation, et représente ainsi, une alternative durable pour la dépollution de l’air intérieur. Parmi les COVs détectés dans l’habitacle, les alcanes sont les plus représentés, avec plus de 50% [2]. Dans la limite de nos connaissances l’oxydation photocatalytique du n-pentane n’a été que très peu étudiée dans la littérature, malgré sa présence non négligeable dans l’habitacle [3]. La photocatalyse est basée sur l’activation d’un matériau semi-conducteur, à température ambiante, sous irradiation (d’énergie supérieure ou égale à sa bande interdite) créant ainsi des espèces actives, telles que O2°- et OH°. De part leur fort pouvoir oxydant ces radicaux vont oxyder le polluant cible. Les travaux présentés ici sont une première approche de la dégradation photocatalytique du n-pentane à température ambiante par le TiO2 DEGUSSA P25 (86%m. Anatase, 14%m. Rutile). L’influence de plusieurs paramètres est étudiée telle que la concentration en n-pentane (25ppm-300ppm), le débit molaire, le flux de photons à 365nm (5mW/cm2 et 0.5mW/cm2), l’impact de l’humidité relative (0%-90%). Le travail à différents débits molaires permet de prédire les performances photocatalytiques dans des conditions proches de celles trouvées dans l’habitacle.Les résultats montrent qu’une minéralisation complète en CO2 est toujours obtenue dans ces conditions (figure 1).RemerciementLes auteurs remercient le Ministère français de l’Enseignement Supérieur et de la Recherche pour la bourse de thèse de Marième Bouhatmi.