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The effect of a reduction step on the catalytic activity of Pd supported doped ceria catalysts was investigated for the propane combustion. Two different oxides based on ceria zirconia (CZ), as a reference three-way catalyst support, and Gadolinia doped ceria (GDC), a mixed ionic electronic conductor, have been used to support Pd nanoparticles. The samples were characterized by H-CO chemisorption, temperature programmed reduction, and XPS. In addition, the reduction step in H was in situ observed by environmental transmission electron microscopy. It was found that the catalytic activity of Pd supported on ceria-based supports can be strongly promoted by a reduction step whereas it does not change on alumina. This effect was attributed, in particular on GDC, to the reduction of a surface interaction phase, PdCeO, which induces a re-dispersion of metallic Pd nanoparticles. [ABSTRACT FROM AUTHOR]

A catalyst based on Pd and Rh nanoparticles supported on a Gadolinia-Doped Ceria support, a mixed O/e ionic electronic conductor (MIEC), has been prepared and washcoated in SiC catalyzed gasoline particulate filters (cGPF) prototypes. These filters have been prepared and tested for the aftertreatment of gasoline direct injection engine exhausts. Catalytic performances of various configurations of cGPFs (different catalyst loadings and locations) have been carried out near real conditions and compared with those of a commercial three-way converter TC as well as a monolith washcoated with the same MIEC-supported catalyst. Among all the samples tested, the most promising one is a GPF equipped with a SiC filtration membrane on which a catalytic layer has been washcoated. This cGPF combines good filtering efficiency, due to the membrane, and remarkable catalytic performances in presence of soot and water. The catalytic performance is greater than those of a commercial TC, in spite of a 9 times lower platinum group metal loading. This is attributed to both self-sustained electrochemical promotion and a higher availability of the active sites localized on the membrane. [ABSTRACT FROM AUTHOR]

Nanoparticles of platinum were dispersed on an oxygen ionically conducting support, Yttria-Stabilized Zirconia (YSZ), on non-doped zirconia and on silica. The role of the support oxygen lattice in the mechanism of propane deep oxidation was investigated by using O Temperature-Programmed Desorption, catalytic activity measurements using isotopic oxygen, and isotopic exchange experiments. The results emphasize that the propane combustion mechanism on Pt/YSZ presents a different pathway compared with that involved on Pt/SiO and Pt/ZrO because, propane is preferentially oxidized by lattice YSZ oxygen species on Pt/YSZ. Strong Pt nanoparticles/YSZ interactions generate a promoted state similar to that observed on polarizations during electrochemical promotion of catalysis. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This study has shown that the phenomenon of electrochemical promotion of catalysis or NEMCA effect can be used to activate a metal catalyst for the propene deep oxidation in the presence of water in the feed and in both stoichiometric and lean-burn conditions. The electrochemical catalysts were based on sputtered Pt films interfaced with gadolinium-doped ceria solid electrolyte. This system allows implementing NEMCA effect at quite low temperatures and electrochemical activation of propene deep oxidation was evidenced at temperatures as low as 190 °C. In addition, a new design of electrochemical catalysts was proposed by depositing a interlayer of strontium-doped lanthanum manganite between the CGO dense support and an ultra-thin coating of Pt. This concept allows to drastically decrease the Pt loading since the electronic conductivity is ensured by the perovskite layer. [ABSTRACT FROM AUTHOR]

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Electrochemical catalysts based on Pd deposited by Physical Vapour Deposition on YSZ were used for methane deep oxidation. Different thicknesses of Pd films varying from 11 to 75 nm were catalytically characterized between 150 and 750 °C. The Pd loadings were extremely low. Catalytic and EPOC experiments were carried out on those electrochemical catalysts. Their catalytic activities were compared with the performances of a reference catalyst. It was found that the catalytic activity can be in situ tuned by applying an anodic polarization thus supplying oxygen ions at the surface of the catalyst. Faradaic efficiency values up to 258 were observed and the induced modifications of the catalytic rate were typically 100 times higher than the corresponding ionic current. The influence of the polarization on the temperature of decomposition of the palladium oxide was also examined. The polarization was found to enhance the thermal stability of the oxide and turn palladium oxide into metallic palladium at higher temperatures. [ABSTRACT FROM AUTHOR]

Electrochemical catalysts based on LSM deposited on YSZ were used for propane deep oxidation. Electrochemical characterizations such as impedance spectroscopy and current–overpotential measurements were performed. Different thicknesses of LSM films were catalytically characterized and EPOC experiments were carried out on those electrochemical catalysts. It was found that the reaction rates can be in situ tuned by applying an anodic polarization but with weak promotional effects. The faradaic efficiency decreased as the applied potential, the temperature, and the thickness of the catalyst increased. [ABSTRACT FROM AUTHOR]

Two series of electrochemical catalysts were prepared from sputtered Pt thin films onto two kinds of electrolyte membranes, 8 mol% Y2O3-stabilized ZrO2 (YSZ), an O2− conducting oxide and Na3Zr2Si2PO12 (NASICON), a Na+ one; respectively. The thickness of the Pt films varied from 8 to 120 nm. Therefore, the Pt loading was extremely low. The catalytic activity of Pt/YSZ and Pt/NASICON systems has been investigated between 200 and 500 °C for propane and propene, respectively. In spite of the low Pt loading, the Pt/YSZ electrochemical catalysts exhibited high activity for propane combustion. Furthermore, the catalytic activity can be in-situ controlled by applying electrical polarisation with high Faradaic efficiency (103). The catalytic rate of propene deep oxidation on Pt/NASICON electrochemical catalyst was found to be limited by the number of active sites, which is low on very thin Pt films. Moreover, initial anodic polarisation indicate that Na+ ions are already present on the top surface of Pt, probably proceeding from the preliminary stabilisation treatment of Pt in the reactive mixture. Nevertheless, polarisation allows the tuning of the catalytic activity of the electrochemical catalysts for propene oxidation. Finally, for both kinds of electrochemical catalysts, our results have evidenced that the measurement of the open-circuit voltage during catalytic process can be an indicator of the hydrocarbon conversion. [ABSTRACT FROM AUTHOR]

The origin of the electrochemical promotion of catalysis (EPOC) was investigated via oxygen temperature-programmed desorption (O2-TPD) from a polycrystalline Pt film interfaced with YSZ. TPD experiments were carried out under operating conditions similar to those used for catalytic activity measurements. This study has clearly shown that an anodic current generates the migration of “backspillover” ionic oxygen species from YSZ toward the Pt surface. These ionic species act as promoters and enable the formation of weakly adsorbed oxygen species coming from the gas phase which are more reactive and thus responsible for the activity enhancement. The effect of polarization is to carry or to remove the promoting ionic species on the Pt surface. Therefore, electrochemical promotion of catalysis can be considered as an electrically controlled metal support interaction, where the support is an O2− conducting solid electrolyte. [ABSTRACT FROM AUTHOR]

Electrochemical catalysts were used for environmental applications, such as the clean production of energy from propane and propene combustion, the elimination of VOC's like propene and the NOx abatement All the selected electrochemical catalysts were composed of a Pt film deposited on YSZ, NASICON or CGO. It was found that all these chemical reactions can be electropromoted. Moreover, the reaction rates can be in-situ tuned by applying a polarisation. Furthermore, the selectivity of Pt-based electrochemical catalysts can be modified in order to avoid the formation of pollutant. Finally, EPOC can improve the lifetime of a catalyst by inhibiting its poisoning by carbonaceous species. [ABSTRACT FROM AUTHOR]

8 to 120 nm-thick Pt coatings were sputter-deposited on Yttria-Stabilised Zirconia (YSZ) membranes, 17 mm in diameter, by magnetron sputtering of a Pt target at low pressure (0.3 Pa). The catalytic activity of propane combustion under open-circuit conditions is first measured near to the stoichiometry (0.2%C3H8/1%O2) and shows that the coatings present a rather high catalytic activity. Close-circuit measurements were finally performed at 337 °C and 400 °C. They show that rather high faradaic efficiencies in the range 106 can be reached as soon as the Pt film is thick enough to allow a bias of its whole area. [ABSTRACT FROM AUTHOR]

This study deals with the relationship between open-circuit potential and catalytic activity of the system Pt/YSZ. Temperature-programmed desorption (TPD) of oxygen was carried out in order to investigate the link between the oxygen coverage and the potential. Then, catalytic activity in parallel with the potential value was measured between 200 °C and 500 °C for NO oxidation, C3H8 combustion, C3H6 combustion and the selective catalytic reduction (SCR) of NO by C3H6 in the presence of oxygen. It was found that potential measurement can give precious information on the competitive adsorption between oxygen and other reactants. Finally, it seems to be also a good way to anticipate the NEMCA behavior for reactions, which involve oxygen. [ABSTRACT FROM AUTHOR]

The combustion of light hydrocarbons finds an important application in volatile organic compounds (VOCs) abatement. Catalytic combustion is interesting in this domain, because it may be carried out at relatively low temperatures and under large air excess. For this purpose, precious metal-based catalysts are very performing, but the quest for a lower-cost alternative solution is necessary. In this field, conducting mixed oxides such as perovskites are good candidates, especially when they are electrochemically promoted. The present work shows that electrochemical promotion of catalytic activity (NEMCA effect) in propene total combustion can be carried out with La0.8Sr0.2Co0.8Fe0.2O3, an electron-conducting perovskite-type oxide, deposited on YSZ. [ABSTRACT FROM AUTHOR]

The catalytic activity of polycrystalline Pt deposited on Yttria Stabilized Zirconia (YSZ) for the oxidation of propane to CO2 can be affected using the effect of Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA). It was found that by applying positive overpotentials and thus, supplying O2- onto catalyst surface, up to 3.2-fold increase in the catalytic rate of C3H8 oxidation could be obtained at 365 °C. At 305 °C, no effect was evidenced. Using cyclic voltammetry and impedance spectroscopy, we have shown the modifications induced by the addition of C3H8 on the kinetics of the 02, Pt/YSZ interface in the temperature range 300–400 °C. A decrease of the coverage of adsorbed oxygen species produced electrochemically was evidenced as well as a decrease of the oxygen electrode reaction rate under anodic potential. [ABSTRACT FROM AUTHOR]

The reduction of NO by C3H6 in the presence of oxygen, is of great environmental importance. Platinum-based catalysts are very active but not selective towards N2 production and mainly convert NO into N2O, which participates to the greenhouse effect. Moreover, their operating temperature window is quite narrow. Electrochemical promotion was used to improve platinum catalytic behaviour. Platinum was deposited on YSZ (Y2O3 — stabilised ZrO2), an O2-conductor. It was found that a negative current increased the rate of NO reduction and CO2 formation. This rate enhancement was non-Faradaic with an apparent Faradaic efficiency (Λ) close to 180 indicating the manifestation of a NEMCA effect. However, the current application had no effect on the N2 selectivity [ABSTRACT FROM AUTHOR]

The electrochemical behavior of pure lanthanum chromite and strontium dopedlanthanum chromite was studied by impedance spectroscopy under H2/H2O, CO/CO2 and CH4/H2O. Results show that the electrochemical oxidation of H2 is faster than that of CO or CH4. Strontium doping enhances the anodic activity of the material. The impedance diagrams are composed of two semi-circles. The high frequency one does not appear to be related to a chemical or electrochemical reaction. The low frequency one is linked to the nature and concentration of the electroactive species. [ABSTRACT FROM AUTHOR]