Improvement of the NOx selectivity for a planar YSZ sensor

International audienceIn recent years planar yttria-stabilized zirconia (YSZ) based electrochemical gas sensors for automotive exhaust applications have become a major source of interest. The present work aims to develop a sensor for industrialisation. For this reason planar YSZ-based electrochemical sensors using two metallic electrodes (platinum and gold) were fabricated using screen-printing technology and tested in a laboratory test bench for different concentrations of pollutant gas such as CO, NO, NO2 and hydrocarbons in oxygen rich atmosphere. It was furthermore shown that the selectivity towards NOx could be highly reinforced by deposing a catalytic filter consisting of 1.7-4.5 wt.% Pt dispersed on alumina directly on the sensing elements. This filter was characterized by the use of SEM, TPD and XRD

Improvement of the NOx selectivity for a planar YSZ

International audienceThe present work aims to develop a sensor that can leave the laboratory and be industrialised. For this reason potentiometric sensors based on a solid electrolyte YSZ and 2 metallic electrodes (platinum and gold) were fabricated by screenprinting technology and were tested in a laboratory test bench for different concentrations of CO, NO and NO2 in oxygen rich atmosphere. By deposing a catalytic filter consisting of 1.7%Pt dispersed in alumina directly on the electrodes, it was shown that the selectivity towards NOx could be highly reinforced. This filter was characterized by the use of SEM, TPD, and XRD technology

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

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

Catalyseurs conducteurs ioniques pour l'oxydation des suies.

nationa

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

Recent advances in Electrochemical Promotion of Catalysis

International @ AIR+PVE:MTS:FSA:ABOInternational audienceIonically conducting ceramics can be utilized as active catalyst supports in a solid electrolyte cell. In this case, the electrochemical cell is then called electrochemical catalyst and one of the electrodes is also a catalyst. Gaseous reactant mixture (e.g. a mixture of C2H4 and O2) is fed over the catalyst-electrode. Considering an oxygen conducting ceramic, the application of a potential (ą2 V) between the catalyst and a counter electrode induces the migration of oxygen ions, O2-, which are in situ supplied or removed from the catalyst during the catalytic experiments. It has been found that, rather surprisingly, this oxygen pumping operation, can lead over a wide temperature range (220-550°C) to very pronounced and non-Faradaic reversible modifications in the catalytic activity (changes that are not proportional to the current), frequently accompanied by very significant changes in product selectivity. This phenomenon is known in the literature either as Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or, more commonly in recent years, as Electrochemical Promotion of Catalysis (EPOC). EPOC has been investigated by a variety of techniques which merge to the conclusion that this process is due to electrochemically controlled migration (spillover or reverse spillover) of promoting or poisoning ionic species from the ceramic support to the catalyst surface. These ionic species are accompanied by their image charge in the metal, thus forming overall neutral dipoles which decorate the catalyst surface. In-situ electrochemically supplied ions act as promoting or inhibiting agents for the reaction. EPOC can be considered as an electrochemically controlled metal support interaction Starting from model reactions, i.e. propane and propylene deep oxidation, and from a model electrochemical catalyst, i.e. Pt/YSZ (Yttria-Stabilized Zirconia, an O2- conductor), this lecture will give an overview of recent advances in the EPOC mechanism understanding as well as in the quest for EPOC of dispersed catalysts

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