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

CAractérisation des Particules des VEhicules Récents et leur Évolution Atmosphérique (CaPVeREA) - Impact de la dilution et de la température sur l'émission des particules et leurs caractérisations

This report aims at improving knowledge on dilution ratio and temperature impact on particle emission. All experiments have been performed at chassis dynamometer bench with Euro 5 gasoline (DI) and Euro 5 Diesel (DPF) vehicles. Particle missions at different dilution ratio and temperature have been characterized directly at tailpipe and compared with CVS results. Dilution and temperature impacts showed that the nucleation, condensation and coagulation phenomena were favored at low dilution ratio (3-16) and temperature (50°C), which indicated that the CVS condition - low temperature and low dilution ratio - was not optimal and might induce artifacts on particle quantification. Different analytical techniques were also used to characterize ultrafine particles with diameter less than 30 nm. Particle morphology has been characterized using Electron Microscopy (MEB and MET). Chemical identification using mass spectrometry will be presented in next report.Dans le cadre du projet CaPVeREA, nous proposons une étude dédiée pour caractériser l'influence de conditions de prélèvement et de mesure (taux de dilution et température) sur l'émission des particules ultrafines. La mise en oeuvre de mesures d'émission à l'échappement et après CVS d'un Îhicule à injection directe d'essence (IDE) et Diesel Euro 5 a été réalisée. Les facteurs d'émissions ont été caractérisés au cours d'une campagne d'essais réalisée au banc à rouleaux et les résultats entre échappement et CVS ont été comparés. Les effets de la dilution et de la température montrent que les phénomènes de nucléation, de condensation et de coagulation sont favorisés à faible ratio de dilution (3-16) et de température (50°C). Ceci indique que les conditions de CVS, de basse température de dilution primaire, ne sont pas optimales et pourraient favoriser des éventuels artéfacts sur la quantification de particules. Différentes techniques analytiques ont été évaluées en regard de leur potentiel d'analyse des particules ultrafines de diamètre inférieur à 30 nm. La morphologie des particules sera caractérisée à l'aide de la microscopie électronique (MEB et MET). L'identification des espèces chimiques par spectrométrie de masse sera réalisée dans les phases suivantes du projet

Dilution effects on ultrafine particle emissions from Euro 5 and Euro 6 diesel and gasoline vehicles

SSCI-VIDE+CARE+BDA:ABODilution and temperature used during sampling of vehicle exhaust can modify particle number concentration and size distribution. Two experiments were performed on a chassis dynamometer to assess exhaust dilution and temperature on particle number and particle size distribution for Euro 5 and Euro 6 vehicles. In the first experiment, the effects of dilution (ratio from 8 to 4000) and temperature (ranging from 50 °C to 150 °C) on particle quantification were investigated directly from tailpipe for a diesel and a gasoline Euro 5 vehicles. In the second experiment, particle emissions from Euro 6 diesel and gasoline vehicles directly sampled from the tailpipe were compared to the constant volume sampling (CVS) measurements under similar sampling conditions. Low primary dilutions (3-5) induced an increase in particle number concentration by a factor of 2 compared to high primary dilutions (12-20). Low dilution temperatures (50 °C) induced 1.4-3 times higher particle number concentration than high dilution temperatures (150 °C). For the Euro 6 gasoline vehicle with direct injection, constant volume sampling (CVS) particle number concentrations were higher than after the tailpipe by a factor of 6, 80 and 22 for Artemis urban, road and motorway, respectively. For the same vehicle, particle size distribution measured after the tailpipe was centred on 10 nm, and particles were smaller than the ones measured after CVS that was centred between 50 nm and 70 nm. The high particle concentration (H106 #/cm3) and the growth of diameter, measured in the CVS, highlighted aerosol transformations, such as nucleation, condensation and coagulation occurring in the sampling system and this might have biased the particle measurements

Pr-rich cerium-zirconium-praseodymium mixed oxides for automotive exhaust emission control

International audienceThis study describes the textural, structural, redox properties, oxygen reactivity of two Pr-rich cerium-zirconium-praseodymium (CZP) oxides (Ce 0.45 Zr 0.10 Pr 0.45 O 2-x and Ce 0.475 Zr 0.05 Pr 0.475 O 2-x) and their catalytic activity for propane and CO oxidation in both stoichiometric and lean conditions, two important reactions for automotive exhaust emission control. The concentration of oxygen vacancies can be tuned by the quantity of Pr 3+ cations which depend both on the preparation method and the composition. The Pr 4+ (4f 1)/Pr 3+ (4f 2) ratio was accurately determined by magnetic measurement. A highly energetic grinding step was found to double this Pr 3+ concentration, resulting in a strong enhancement of the lowtemperature reducibility, bulk oxygen mobility and catalytic activity for propane deep oxidation. Pr-rich CZP oxides seem to be less relevant for CO oxidation, which is mainly driven by the specific surface areas. These Pr-rich CZP mixed oxides present better performances for lean conditions, suggesting their possible role in diesel oxidation catalysts applications

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution

Secondary organic aerosol formation from photo-oxidation of toluene with NOx and SO2: Chamber simulation with purified air versus urban ambient air as matrix

SSCI-VIDE+CARE+ABO:CGOInternational audienceChamber studies on the formation of secondary aerosols are mostly performed with purified air as matrix, it is of wide concern in what extent they might be different from the situations in ambient air, where a variety of gaseous and particulate components preexist. Here we compared the photo-oxidation of "toluene + NOx + SO2" combinations in a smog chamber in real urban ambient air matrix with that in purified air matrix. The secondary organic aerosols (SOA) mass concentrations and yields from toluene in the ambient air matrix, after subtracted ambient air background primary and secondary organic aerosols, were 9.0-34.0 and 5.6-12.9 times, respectively, greater than those in purified air matrix. Both homogeneous and heterogeneous oxidation of SO2 were enhanced in ambient air matrix experiments with observed 2.0-7.5 times higher SO2 degradation rates and 2.6-6.8 times faster sulfate formation than that in purified air matrix, resulting in higher in-situ particle acidity and consequently promoting acid catalyzed SOA formation. In the ambient air experiments although averaged OH radical levels were elevated probably due to heterogeneous formation of OH on particle surface and/or ozonolysis of alkenes, non-OH oxidation pathways of SO2 became even more dominating. Under the same organic aerosol mass concentration, the SOA yields of toluene in purified air matrix experiments matched very well with the two-product model curve by Ng et al. (2007), yet the yields in ambient air on average was over two times larger. The results however were much near the best fit curve by Hildebrandt et al. (2009) with the volatility basis set (VBS) approach. (C) 2016 Published by Elsevier Ltd