Caroline Tardivat

An all porous solid oxide fuel cell (SOFC): a bridging technology between dual and single chamber SOFCs

A novel concept that employs dual chamber SOFC technology with a porous electrolyte, which allows the controlled distribution of gaseous O2 at the anode side, was successfully designed using an all porous structure. The oxidative reforming of hydrocarbon streams can consequently operate in a similar fashion to single chamber SOFCs, but within a safer, better controlled process.

Role of Lattice Oxygen in the Propane Combustion Over Pt/Yttria-Stabilized Zirconia : Isotopic Studies

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 18O2 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/SiO2 and Pt/ZrO2 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

Mixed Ionic–Electronic Conducting Catalysts for Catalysed Gasoline Particulate Filters

A catalyst based on Pd and Rh nanoparticles supported on a Gadolinia-Doped Ceria support, a mixed O2−/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.

The role of lattice oxygen in CO oxidation over Ce18O2-based catalysts revealed under operando conditions

Ceria-based materials are today the most prominently used catalyst supports for CO oxidation and NOx reduction in three-way catalytic converters (TWCs) worldwide. Acting as oxygen buffer compounds, the underlying reaction mechanism and especially the distinct role of surface and lattice oxygen for catalytic reactions are still under debate. This is partially related to the complexity of the real CeO2 surface containing important amounts of water and carbonates. Combining TG-MS, Raman spectroscopic experiments and isotope labeling pulse temperature programmed oxidation reaction (ILPOR), coupled with mass spectrometric analysis of 18O-doped ceria, we explored here the oxygen uptake/release behavior under operando conditions, together with the catalytic activity related to surface and/or lattice oxygen mobility and exchange. Specific changes in the lattice dynamics induced by 18/16O isotope exchange were analyzed by Raman spectroscopy, allowing the temperature-dependent onset of lattice oxygen mobility and isotope exchange behavior to be studied selectively. For Pt-supported nano-ceria, we evidenced high catalytic performance for CO oxidation, activated slightly above ambient conditions without significant lattice oxygen participation. The distinct role of surface and lattice oxygen in the catalytic reaction of ceria catalysts is discussed as a function of temperature, grain size, Gd doping and Pt impregnation.

High specific surface area YSZ powders from a supercritical CO2 process as catalytic supports for NOx storage–reduction reaction

Nanometric yttria-stabilized zirconia (3 mol% yttria, SC-3YSZ) was synthesized using an innovative supercritical carbon dioxide-aided sol–gel process and used as a support for NOx storage catalysts. Wash-coats composed of noble metals (Pt and Rh) dispersed on 3YSZ were deposited inside the porosity of mini-diesel particulate filters. Commercial and SC-3YSZ powders were used as supports independently and mixed. NOx storage/reduction performances were compared under cycling conditions according to the YSZ support surface area, the washcoat localization inside the DPF and the metallic dispersions. All the results emphasize that the presence of high specific surface area SC-3YSZ inside the DPF improves the NOx conversion, the N2 selectivity and the NOx storage capacity. This enhancement of the catalytic properties was linked with the increase in both the metallic dispersion and the number of storage sites on the catalyst surface.

Effect of the Reduction Step on the Catalytic Performance of Pd–CeMO2 Based Catalysts (M = Gd, Zr) for Propane Combustion

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 H2–CO chemisorption, temperature programmed reduction, and XPS. In addition, the reduction step in H2 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, PdxCeO2−δ, which induces a re-dispersion of metallic Pd nanoparticles.

Coke-free operation of an all porous solid oxide fuel cell (AP-SOFC) used as an O2 supply device

Suppressing carbon deposition is crucial for operating solid oxide fuel cells (SOFCs) in dry hydrocarbon fuels. To prevent flammability and carbon deposition issues, a novel all porous SOFC (AP-SOFC) was developed as an O2 supply device. In the present work, cell performances were studied using an anode-supported thin-film Gd0.1Ce0.9O1.9 (CGO) configuration prepared by dry-pressing. The cell performance in a CH4–He mixture was improved over 14 times compared to an all porous electrolyte-supported SOFC. The peak power density of 183 mW cm−2 was obtained with 112 μm CGO porous electrolyte at 700 °C. The long-term operational stability of the AP-SOFC was investigated with CH4 and C3H8 under OCV conditions and with CH4 under a constant current of 450 mA cm−2. The anode-supported AP-SOFC was stable in CH4 fuel for at least 10 days without observable coking of the anode. This indicates that the operation of an AP-SOFC in hydrocarbon fuels is a feasible process. An additional advantage of such a process is improved safety, due to the distribution of O2 along the anode.

In situ generated catalyst: Copper (II) oxide and Copper (I) supported on Ca2Fe2O5 for CO oxidation

Two sets of copper oxide–brownmillerite Ca2Fe2O5 catalysts are prepared and studied for CO oxidation. The first set of catalysts is prepared by classical wet impregnation of the Ca2Fe2O5 support. The second set is prepared by Ca2Fe2O5 B-site doping. The active catalyst species are generated during hydrogen treatment. The two sets of catalysts behave very differently in CO oxidation. The performance of the impregnated catalysts is independent of the Cu content, while the performance of the doped catalysts can be tuned by the copper content. The best performing catalyst is a doped-reduced catalyst with 40 mol% Cu. Detailed characterization of the catalysts is carried out using nitrogen physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption fluorescence spectroscopy (XAFS).