Caractérisations des émissions particulaires des moteurs IDE : masse, nombre, taille, nature. Utilisation d’un filtre à particule commercial.

SSCI-VIDE+CARE+ABOInternational audienceLa 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

evaluation des processus photocatalytiques pour la depollution de l’air

SSCI-VIDE+CARE+CGO:ABOInternational audienceLa pollution atmosphérique est devenue un des problèmes majeurs des mégapoles. Ce problème n’est donc pas nouveau, il est néanmoins loin d’être résolu et ce, d’autant plus que la transformation des grandes agglomérations en réelles mégapoles est susceptible de lui conférer une importance renouvelée. Des solutions de remédiation active sont proposées dans les lesquelles des matériaux photocatalytiques sont (ou vont être) déployés dans les sites urbains afin d’agir en tant que puits pour certains polluants tels que les oxydes d’azote et des composés organiques volatils et aromatiques dans l’environnement urbain. Ainsi, des produits basés sur les propriétés photocatalytiques d’une fine couche de dioxyde de titane déposée à la surface de matériaux urbains (verre, pavés, etc.) ou intégrés dans les peintures ou enduits (bétons) ont été lancés sur le marché européen et sont suggérés êtres des pièges actifs pour de nombreux polluants. Dans le cadre du projet européen PhotoPAQ, nous avons évalué la faisabilité de l’utilisation des ces matériaux à base de TiO2 pour atténuer les problèmes de la pollution de l'air sous conditions atmosphériques réelles. Ainsi, cette présentation abordera les aspects suivants•test des activités photocatalytiques des produits à base de TiO2 disponibles sur le marché de manière à évaluer leur efficacité en matière de réduction de la pollution ;•conception d’indicateurs environnementaux et de méthodes d’évaluation mieux adaptés à la mesure de l’impact de ces nouvelles technologies et application dans les villes européennes ;•proposition de recommandations et d’un « outil de démonstration » pour les collectivités territoriales européennes sur les applications pratiques de ces techniques pour le traitement de l’air

Electrochemical promotion of Ag catalyst for the low temperature combustion of toluene

International audienceThis paper is the first report on the possibility to electrochemically promote the catalytic complete oxidation of toluene on Ag films deposited on Y2O3 stabilized ZrO2 (YSZ) at relatively low temperature (300°C). It was found that the toluene conversion into CO2 and H2O on an Ag catalyst can be significantly promoted upon cathodic polarization, i.e. oxygen removal from the catalyst surface. Such an enhancement is strongly non-Faradaic. Conversely, anodic polarization, i.e. O2- supplying from the YSZ support toward the catalyst, has no significant influence on the activity of Ag film. The promotion effect is therefore typically an electrophilic one. Further investigation indicates that there are some optimum values for the negative potential or current. Beyond these values, the activity of catalyst remains the same, but the Faradaic efficiency decreases

Mechanism investigations of soot oxidation over Ag-supported YSZ.

SSCI-VIDE+CARE+ASR:ABO:PVEInternational audienceAs Particulate Matter (PM) vehicle emissions are regulated by US/EU standards, the use of DPF (Diesel Particle Filter) has been widely spread to comply with the regulations. The main problematic associated with DPF comes from its regeneration. Numerous silver supported catalysts have been reported as active materials for soot oxidation [1,2]. Such activity is explained by the ability to provide oxygen to the soot and by the mobility of silver at the surface of the catalyst. We investigated the soot oxidation mechanism by silver nanoparticles supported over a non-reducible, ionic conductor oxide: Yttria-Stabilized Zirconia (YSZ). YSZ is an active support for soot oxidation thanks to its bulk oxygen mobility [3,4]. This study reports the mechanism of soot on Ag/YSZ catalysts by using isotopic temperature programmed oxidation (TP18O2), isotopic isotherm and isotopic oxygen exchange

Photosensitized formation of secondary organic aerosols above the air/water interface

International audienceIn this study, we evaluated photosensitized chemistry at the air−sea interface as a source of secondary organic aerosols (SOA). Our results show that, in addition to biogenic emissions, abiotic processes could also be important in the marine boundary layer. Photosensitized production of marine secondary organic aerosol was studied in a custom-built multiphase atmospheric simulation chamber. The experimental chamber contained water, humic acid (1−10 mg L −1) as a proxy for dissolved organic matter, and nonanoic acid (0.1−10 mM), a fatty acid proxy which formed an organic film at the air−water interface. Dark secondary reaction with ozone after illumination resulted in SOA particle concentrations in excess of 1000 cm −3 , illustrating the production of unsaturated compounds by chemical reactions at the air−water interface. SOA numbers via photosensitization alone and in the absence of ozone did not exceed background levels. From these results, we derived a dependence of SOA numbers on nonanoic acid surface coverage and dissolved organic matter concentration. We present a discussion on the potential role of the air−sea interface in the production of atmospheric organic aerosol from photosensitized origins. ■ INTRODUCTION Although the dominant mass fraction of sea-spray aerosol is inorganic sea salt, organic matter can also contribute to the overall mass of aerosols in the marine boundary layer (MBL). 1,2 Recent field measurements clearly documented the presence of organic matter in oceanic particles. 3,4 Cavalli et al. 5 and O'Dowd et al. 6 found a significant and dominating fraction of organic matter in the submicrometer size range, while the supermicrometer size range predominately consisted of inorganic sea salt. During high biological activity, the organic fraction ranges from 40 to 60% of the submicrometer aerosol mass, while during low biological activity periods, this fraction decreases to 10−15%. Concentrations of organic aerosol mass in air advected over regions of high biological activity were up to 4 μg m −3 and comparable to polluted air masses. 7 The concentration of organic aerosol formed by secondary processes has also been correlated with biological activity. 8 Volatile sulfur species greatly impact the formation of secondary marine aerosols 9−13 and are included in general circulation models predicting climate evolution. 13−15 Together, these findings potentially link ocean biota with marine derived organic aerosols. 16 As a result, the organic fraction of the marine aerosols as well as the trace gas composition over the ocean are controlled by the chemical and physical properties of the sea-surface microlayer (SML). 17−19 Indeed, recent studies reported the use of natural seawater to generate sea spray aerosol (SSA) in order to evaluate how SML composition drives the composition and associated properties of freshly emitted SSA. 20,21 Organic material present at the sea surface includes amphiphiles derived from oceanic biota (fatty acids, fatty alcohols, sterols, amines, etc.) and more complex colloids and aggregates exuded by phytoplankton, which mainly consist of lipopolysaccharides. 22−31 All of these compounds can be highly enriched in this microlayer. 32,33 The presence of complex and potentially photoactive compounds, such as a fatty acid film at the air−sea interface and therefore in the primary marine aerosol, was reported on the surface of continental and marine aerosols. 34−36 This could give rise to the assumption that new processes affect the chemistry in the MBL. Indeed, Reeser et al. 37,38 showed that photoexcited chlorophyll can oxidize halide anions at the salt water surface, producing atomic halogens. A similar chemistry is expected for nitrate and nitrite anions, suggesting a rich new source of oxidants in the MBL. These studies stress the need for a better understanding of the chemistry and potential photochemistry of the surface micro-layer. Indeed, the photochemistry at the air−sea interface has not been adequately considered over the past years. 39 Previous works from our group have shown that such photochemical processing of a surfactant in the presence of a photosensitizer led to the formation of unsaturated and highly functionalized volatile organic compounds (VOCs). 40,41 The use of humic acid as a photosensitizer initiates chemical transformation of surfactants, such as nonanoic acid 40 and octanol, 41 through multiple pathways. The initial step is H-abstraction on the alky

Unravel the mechanism of soot oxidation over silver-supported Yttria-Stabilized Zirconia through isotopic experiments

SSCI-VIDE+CARE+ABO:PVENational audience1. 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

Isotopic Oxygen Exchange Study to Unravel Noble Metal Oxide/Support Interactions: The Case of RuO2 and IrO2 Nanoparticles Supported on CeO2, TiO2 and YSZ

SSCI-VIDE+CARE+ABO:ACV:PVEInternational audienceThe 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

Catalyseurs conducteurs ioniques pour l'oxydation des suies.

nationa

Mechanism investigations of soot oxidation over Ag-supported YSZ.

SSCI-VIDE+CARE+ASR:ABO:PVEInternational audienceAs Particulate Matter (PM) vehicle emissions are regulated by US/EU standards, the use of DPF (Diesel Particle Filter) has been widely spread to comply with the regulations. The main problematic associated with DPF comes from its regeneration. Numerous silver supported catalysts have been reported as active materials for soot oxidation [1,2]. Such activity is explained by the ability to provide oxygen to the soot and by the mobility of silver at the surface of the catalyst. We investigated the soot oxidation mechanism by silver nanoparticles supported over a non-reducible, ionic conductor oxide: Yttria-Stabilized Zirconia (YSZ). YSZ is an active support for soot oxidation thanks to its bulk oxygen mobility [3,4]. This study reports the mechanism of soot on Ag/YSZ catalysts by using isotopic temperature programmed oxidation (TP18O2), isotopic isotherm and isotopic oxygen exchange

Electrochemical Promotion of Catalysis mechanistic studies utilizing isotopical labeling

International @ AIR+MTS:FSA:ABO:PVEInternational audienceElectrochemical promotion of catalysis (EPOC) is a very promising concept for boosting catalytic processes and advancing the frontiers of catalysis. EPOC utilizes electrochemical catalysts which are composed of catalytic films interfaced on solid electrolyte membranes. Ions contained in these electrolytes are electrochemically supplied onto the catalyst surface and act as promoting agents to modify the catalyst electronic properties. This study presents, for the first time, an operando investigation of the EPOC mechanism by using isotopic oxygen. Propane and propene combustion were implemented on Pt/YSZ electrochemical catalysts because these two reactions exhibit opposite behaviors upon applied overpotentials. Propane oxidation exhibits an electrophobic enhancement (reaction increases upon positive polarization of the catalyst-electrode) while propene oxidation is electrophilic