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International audience; Lignin electrolysis offers the possibility of cogenerating valuable aromatic compounds and green H2 under mild conditions and with a lower energy cost than traditional water electrolysis. In recent years, significant progress has been accomplished towards this objective through the development of active electrocatalysts and the engineering of cell configuration. This short review gives an overview of the anode materials and cells investigated in acidic and alkaline conditions, below and above 100°C and summarizes the main bottlenecks which remain to be addressed. Low-temperature electrolysers could be integrated in biorefineries to convert lignin into higher-value industrial chemicals with co-generation of hydrogen.

International audience; The production of H2 via electrolysis seems to be the best alternative to traditional catalytic reforming processes. The electrolysis of lignin allows to produce pure H2 while valorizing a low-price biomass waste with (theoretically) lower energy requirements than water electrolysis. Previous studies were published in the last years dealing with the electro-oxidation of lignin on Ni-based catalysts. Ni is a robust non-expensive metal that presents a wide variety of oxidation states and phase transitions. To this date, it is still not completely clear how these states/transitions activate the lignin molecule. The aim of this study is to get more insights into the cleavage of the main chemical bonds present in the complex lignin structure over different Ni oxidation states. A Ni/C catalyst, prepared by the polyol method, was thoroughly characterized and tested for the electro-oxidation of both, lignin and 2-phenoxyethanol, where the latter is a model molecule representative of the quintessential β-O-4 linkage in lignin.

International audience; This study investigates the catalytic activity for soot combustion of Ag nanoparticles dispersed on various supports showing different redox properties. Temperature programmed soot oxidation and isotopic exchange experiments were performed to assess the impact of the soot/catalyst contact, the oxygen partial pressure and the ageing toward activity. Three different contact modes have been used to clearly highlight the catalytic performances: loose, tight and supertight. Whatever the support, in both loose and tight contact modes, the catalytic performances are linked with the Ag surface concentration which was found to be high on zirconia-based catalysts and low on ceria-zirconia. The ignition of the soot combustion process occurs on Ag nanoparticles except for catalysts supported on Yttria-Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, where Ag nanoparticles only promote the run-away of the reaction at higher temperatures. Catalysts based on SiO2, ZrO2 and YSZ exhibit a remarkable hydrothermal stability as performances in tight contact mode are fairly similar after the hydrothermal ageing.

International audience; Photochemical aging of volatile organic compounds (VOCs) in the atmosphere is an important source of secondary organic aerosol (SOA). To evaluate the formation potential of SOA at an urban site in Lyon (France), an outdoor experiment using a Potential Aerosol Mass (PAM) oxidation flow reactor (OFR) was conducted throughout entire days during January-February 2017. Diurnal variation of SOA formations and their correlation with OH radical exposure (OHexp), ambient pollutants (VOCs and particulate matters, PM), Relative Humidity (RH), and temperature were explored in this study. Ambient urban air was exposed to high concentration of OH radicals with OHexp in range of (0.2–1.2)×1012 molecule/(cm3•sec), corresponding to several days to weeks of equivalent atmospheric photochemical aging. The results informed that urban air at Lyon has high potency to contribute to SOA, and these SOA productions were favored from OH radical photochemical oxidation rather than via ozonolysis. Maximum SOA formation (36 µg/m3) was obtained at OHexp of about 7.4 × 1011molecule/(cm3•sec), equivalent to approximately 5 days of atmospheric oxidation. The correlation between SOA formation and ambient environment conditions (RH & temperature, VOCs and PM) was observed. It was the first time to estimate SOA formation potential from ambient air over a long period in urban environment of Lyon.

MICROSCOPIE:RX+CARE:ECI2D:MEME+GFE:MAO:FBS:LBU:CGE:TEP:SLO:PVE; International audience; This study explores the dynamic properties of Pt/CeO2 catalysts to develop active catalytic converters for diesel exhausts. It is now well established that single Pt atoms can be stabilised on ceria surface defects under oxidising conditions. However, their catalytic activity is rather poor. A reducing treatment is required to build more active Pt nanoparticles. A Pt/CeO2 catalyst, containing mainly atomically dispersed Pt species, was exposed to reduction steps either at 250 or 500 °C to build Pt nanoparticles. Their redispersion after oxidising treatments in oxygen at three temperatures (room temperature, 250 °C and 500 °C) as well as in a simulated diesel exhaust gas was deeply investigated using different characterisation techniques such as high angle annular dark field scanning transmission electron microscopy, in situ Raman spectroscopy, in situ X-ray diffraction, X-ray photoelectron spectroscopy and H2-temperature-programmed reduction. The arrangement of close packed Pt clusters is a permanent event at low temperatures (

Understanding and controlling the formation of nanoparticles at the surface of functional oxide supports is critical for tuning activity and stability for catalytic and energy conversion applications. Here, we use a latest generation environmental transmission electron microscope to follow the exsolution of individual nanoparticles at the surface of perovskite oxides, with ultrahigh spatial and temporal resolution. Qualitative and quantitative analysis of the data reveals the atomic scale processes that underpin the formation of the socketed, strain-inducing interface that confers exsolved particles their exceptional stability and reactivity. This insight also enabled us to discover that the shape of exsolved particles can be controlled by changing the atmosphere in which exsolution is carried out, and additionally, this could also produce intriguing heterostructures consisting of metal-metal oxide coupled nanoparticles. Our results not only provide insight into the in situ formation of nanoparticles but also demonstrate the tailoring of nanostructures and nanointerfaces. ©

fff; International audience; Reductive treatments with pulses of CO-rich atmosphere have been used to increase and maintain the low temperature activity of a Pt/CeO2-based oxidation catalyst. A combination of operando infrared thermography and spatiotemporal-resolved quick scanning extended X-ray absorption fine structure spectroscopy on a fixed bed microreactor unraveled that, apart from the pulse length, the reaction atmosphere, and the reactor temperature, also the emerging reaction heat during such activating pulses has a strong influence on the structure and catalytic performance of CO and propylene conversion in the axial direction of a fixed-bed and a monolithic reactor. The reductive pulse activation led to an increase of the integral catalyst activity as well as to the generation of zones of different particle sizes along the catalyst bed. In the case of an activation temperature between 250 and 350 °C and pulse lengths between 5 and 30 s, a hotspot of more than 80 K was observed at the beginning of the catalyst bed. Spatially resolved X-ray absorption spectroscopy indicates that larger and more reduced Pt particles are formed particularly at the beginning of the catalyst bed, whereas its subsequent part is less affected. Both the length of the reductive pulses and activation temperature have a distinct influence on the noble metal particle size. On the basis of these results, a Pt/CeO2 based honeycomb shaped substrate was activated in a similar manner. Spatially resolved gas phase profiling showed different reaction rates at the beginning of the reactor, which indicates that the concept can be transferred also to industrially relevant catalysts. In the future, such an activation procedure might open up the door to a new class of operation strategies, by which individual zones generated in the catalyst bed could be assigned for removal of specific pollutants in the exhaust stream

Embargado hasta 15/12/2023 Valorization of glycerol into high added-value products by photocatalysis can not only create good economic benefits, but also cater to the global low-carbon and energy-saving environmental protection needs. In this study we proposed, for the very first time, to perform the photooxidation of glycerol towards added-value products with homemade WO3 and commercial WO3/TiO2 (DTW5)). Their performance was compared with that of state-of-the-art TiO2-based photocatalysts (Anatase, Rutile, and P25). We found that, while TiO2 favours the total oxidation of glycerol, WO3-based materials exhibit an outstanding selectivity towards one of the most valuable oxidation products: glyceraldehyde. It was attributed to their enhanced acidity, which selectively activates Csingle bondO bonds in glycerol and facilitates the further desorption of glyceraldehyde to the liquid phase. This study establishes therefore a new starting point towards the development of advanced materials for an efficient valorization of glycerol.

This paper investigates a new path to synthesis an ordered nanostructured mesoporous titanosilicate by the assembly of preformed titanosilicate (MTS-9) precursors with triblock copolymers. Silver nanoparticles (AgNPs) with different loadings are supported on MTS-9 composite by two different methods: Deposition Precipitation with Urea (DPU) and Impregnation Reduction with Citrate (IRC). The structure and active component of catalysts were confirmed trough N2 adsorption‐desorption, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and high‐resolution transmission electron microscopy (HRTEM). The influence of catalytic activity of AgNPs supported on MTS-9 has been evaluated in the oxidation of Carbon monoxide (CO). The obtained results emphasize on the improvement of catalytic activity of MTS-9 by AgNPs. A total of CO-oxidation up to 100% was achieved at 240 °C for the catalyst prepared by impregnation reduction with citrate. Indeed, the 0.5% Ag/MTS-9 (IRC) catalyst exhibited a high stability after four continuous runs. Overall, this catalyst could be very suitable for oxidation of carbon monoxide industrial process.

International audience; Supported transition metal materials have been identified as ideal candidates for decades to catalyze various reactions of interest in the fields of hydrocarbon refining, energy and environmental catalysis. As the resources in transition metals on earth are known to be limited, it appears to be of the utmost interest to improve the efficiency of the catalytic materials in achieving the best use of these transition metals, in other words the highest metal accessibility when supported on oxide carriers. The present study demonstrates that the deposition of oxotungstates (with a W surface density of 1.3 W/nm2) coupled with the selective deposition of Rh on the CeO2 surface (via successive strong electrostatic adsorptions of an anionic [RhCl6]3- precursor) significantly reduces Rh sintering after reduction at 600 °C under H2 compared to a W-free CeO2 support. Oxotungstates are found to decrease the number of nucleation sites of CeO2 and, therefore, to act as spacers leading to the isolation of the nucleation sites. Oxotungstates may also act as a physical barrier preventing the sintering of the Rh metallic phase in the course of the reduction step at high temperature. Various morphologies of subnanometric Rh clusters exhibiting a limited atomicity (4 to 13 Rh atoms) were considered and most were found to be consistent with the very low coordination numbers of 4.0 ± 0.2 determined experimentally by EXAFS. The coordination numbers and the H2 chemisorption data led the conclusion that the Rh subnanometric clusters must be at the maximum two to three Rh layers thick and not larger than 5 Rh atoms. The benzene hydrogenation turnover frequencies at 50 °C were found to be similar on both the subnanometric Rh clusters and the 2.5 nm Rh nanoparticles (0.12 ± 0.3 s-1).

International audience

This study reports the catalytic properties of Ag nanoparticles dispersed on mixed ionic and electronic conducting layers of LSCF (La0.6Sr0.4Co0.2Fe0.8O3) for propene combustion. A commercial and a synthesized LSCF powder were deposited by screen-printing or spin-coating on dense yttria-stabilized zirconia (YSZ) substrates, an oxygen ion conductor. Equal loadings (50 &micro, g) of Ag nanoparticles were dispersed via drop-casting on the LSCF layers. Electrochemical and catalytic properties have been investigated up to 300 &deg, C with and without Ag in a propene/oxygen feed. The Ag nanoparticles do not influence the electrochemical reduction of oxygen, suggesting that the rate-determining step is the charge transfer at the triple phase boundaries YSZ/LSCF/gas. The anodic electrochemical performances correlate well with the catalytic activity for propene oxidation. This suggests that the diffusion of promoting oxygen ions from YSZ via LSCF grains can take place toward Ag nanoparticles and promote their catalytic activity. The best specific catalytic activity, achieved for a LSCF catalytic layer prepared by screen-printing from the commercial powder, is 800 times higher than that of a pure Ag screen-printed film.

International audience; Hydrogen production by the electrolysis of plastic-waste was recently suggested as an alternative approach to water electrolysis, owing to its favoured thermodynamics. However, the fundamental aspects of such electro-catalytic process were not studied in detail. Here we propose a new approach to understand the electrolysis of polymers, by the use of model molecules. Our target is to develop a technology for the electrolysis of poly(methyl methacrylate), PMMA, plastic waste. We used methyl pivalate (MP) as a model molecule, since it contains similar functional groups than PMMA. We performed electrolysis experiments in a Polymer Electrolyte Membrane reactor with Nafion® protonic membranes and Pt/C electrodes at low temperatures (

The phenomenon of “Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA)” or “Electrochemical Promotion of Catalysis (EPOC)” has been extensively studied for the last decades. Its main strength, with respect to conventionally promoted catalytic systems, is its capability to modify in-situ the activity and/or selectivity of a catalyst by controlling the supply and removal of promoters upon electrical polarization. Previous reviews have summarized the main achievements in this field from both the scientific and technological points of view. However, to this date no commercial application of the EPOC phenomenon has been developed, although numerous advances have been made on the application of EPOC on catalyst nanostructures (closer to those employed in conventional catalytic systems), and on the development of scaled-up reactors suitable for EPOC application. The main bottleneck for EPOC commercialization is likely the choice of the right chemical process. Therefore, from our point of view, future efforts should focus on coupling the latest EPOC advances with the chemical processes where the EPOC phenomenon offers a competitive advantage, either from an environmental, a practical or an economic point of view. In this article, we discuss some of the most promising cases published to date and suggest future improvement strategies. The considered processes are: (i) ethylene epoxidation with environmentally friendly promoters, (ii) NOx storage and reduction under constant reaction atmosphere, (iii) CH4 steam reforming with in-situ catalyst regeneration, (iv) H2 production, storage and release under fixed temperature and pressure, and (v) EPOC-enhanced electrolysers.

Here we report the influence of surface composition on the NOx removal efficiency of lean NOx trap Pd–La1-xAxCoO3/Al2O3-type catalysts. Three catalysts were prepared by the sequential impregnation of 30 wt.% of La1-xAxCoO3-type perovskites and 1.9 wt.% of Pd over alumina. The following perovskite compositions were used: La0.7Sr0.3CoO3, La0.7Ba0.3CoO3 or La0.5Ba0.5CoO3. The results of X-Ray diffraction, N2 adsorption-desorption at −196 °C, electron microscopy, temperature programmed techniques, and Raman and X-ray photoelectron spectroscopies demonstrated that lanthanum partial substitution by barium promoted the presence of Ba-based phases homogeneously distributed at the surface. This fact together with the higher basicity of Ba than Sr led to an increase of the surface basicity for Ba-doped samples. Likewise, Ba doping also favors the formation of small PdO particles homogenously distributed over the surface in close contact with the perovskite phase. Hence, the interactions between Pd and surface basic sites were also promoted. As a result, 1.9 wt.% Pd–30 wt.% La0.5Ba0.5CoO3/Al2O3 catalyst exhibited the highest NOx adsorption and reduction efficiency. Specifically, the NO global conversion and nitrogen production were as high as 90 % and 72 % at 350 °C, respectively. The enhancement of NOx storage capacity during the lean period is mainly assigned to the displacement of gas/solid equilibrium between NO2 and the available NOx adsorption sites due to the presence of higher concentration of basic sites at the surface. Meanwhile, the promotion of the NOx reduction capacity is due to the higher strength of NOx adsorbed species, which slows down the decomposition rate of NOx adsorbed species. Furthermore, the high proximity of Pd and perovskite phase favors the intermediate compounds diffusion. These results confirmed the excellent NOx removal efficiency of the 30 wt.% La0.5Ba0.5CoO3-based catalyst, even above than Pt-based model catalyst.

SSCI-VIDE+CARE+ACV:PVE:SGI; International audience; This study deals with the catalytic decomposition of N2O into harmless N2 and O2, in view of its potential application to decrease the pollution from internal combustion engines. The key of this work was to pre-reduce a Rh/CeZrOx catalyst under a H2 based atmosphere, in order to enhance the amount of oxygen vacancies in the ceria-based support. The results demonstrated that both, Rh species and oxygen vacancies of the ceria-based support catalyze the N2O decomposition reaction. However, the presence of high concentrations of H2O and O2 strongly inhibited the catalytic activity. Nevertheless, small O2 concentrations maintained the performance. Therefore, the pre-reduced Rh/CeZrOx could be potentially used for the reduction of N2O emitted by internal combustion engines working in stoichiometric conditions. In addition, a short injection of a reducing agent (e. g. H2) allowed to partially recover the initial catalytic activity of the system. All in all, this study proposes a new potential approach to mitigate the overall N2O greenhouse gas emissions

Here we report the effects of the incorporation of palladium into 30% La0.7Sr0.3CoO3/Al2O3 catalyst by different methods on the NOx storage and reduction behaviour. Several catalysts were prepared incorporating four palladium nominal loadings (0.75, 1.5, 2.25 and 3.0%) by doping the perovskite formulation (30% La0.7Sr0.3Co1-yPdyO3/Al2O3) or by wetness impregnation over alumina-supported perovskite (y% Pd-30% La0.7Sr0.3CoO3/Al2O3). The results of X-Ray diffraction, N2 adsorption-desorption at −196 °C, electron microscopy, temperature programmed techniques, Raman and X-ray photoelectron spectroscopies demonstrated that the wetness impregnation method induces the formation of small PdO particles homogenously distributed over the surface in strong interaction with the perovskite. Meanwhile, doping method leads to the formation of a mix between intraframework palladium species and surface agglomerated PdOx particles with weaker interaction with the perovskite phase. Therefore, palladium accessibility and the synergetic effects with the perovskite are lower for Pd-doped samples. The NO-to-NO2 conversion is similar irrespective of the palladium content and the incorporation method. This confirms the perovskite phase as the main active site for NO oxidation. However, NOx adsorption during lean conditions and NOx reduction to N2 during rich periods are significantly promoted after the incorporation of palladium, especially by impregnation method. This enhancement is assigned to better NOx adsorption sites regeneration and to a promotion of NOx reduction rate, respectively. Thus, the best De-NOx performance of Pd-impregnated catalysts is derived from the higher efficient use of the palladium active sites. Among the developed formulations, the 1.5% Pd-30% LSCO/Al2O3 sample shows the best balance between NOx removal efficiency and minimum palladium content. This sample shows a NO removal efficiency and nitrogen yield as high as 86.2% and 69.5%, respectively. Based on these results, the developed formulation is revealed as a promising alternative to the NSR model catalyst (1.5% Pt-15% BaO/Al2O3) for NOx removal in the automotive application.

Studies on CH4 oxidation are of special interest due to the difficulty in activating this particular hydrocarbon, due to the demand of an active catalyst at low temperatures (T50 at 300°C) as well as due to possible deactivation of the catalyst upon exposure at high temperatures [1]. To address these issues, we used Electrochemical Promotion of Catalysis (EPOC), which was discovered in the early 80's and has been studied for more than 100 catalytic systems [2]. EPOC allows for the controlled enhancement of the catalytic activity by potential or small current application between a catalyst (working electrode) supported on a solid electrolyte and an auxiliary electrode. In this study, Pd nanoparticles (2-4 nm) deposited on O2- conductor (YSZ) was used to study the electrochemical promotion of methane oxidation. It was found that EPOC could be used to promote nanodispersed catalysts and enhance the reaction rate at temperatures lower than those that have been observed in previous studies [3,4]

Catalytic and electrocatalytic tests have been carried out in a solid oxide cell for propylene combustion using two different Ag screen-printed films deposited on yttria-stabilized zirconia. Competitive adsorption between oxygen and propylene has been observed at 300 °C. Catalytic performances can be tailored by current application in a non-Faradaic manner. The predominant impact of current applications is to modify the reactivity of oxygen present on the Ag surface. Positive current applications enhance the propylene conversion by producing more reactive oxygen species. This beneficial effect is more pronounced under lean-burn conditions where the oxygen coverage on Ag is high.

Metal-support electronic interactions were investigated in CO oxidation by using a Pd/CeO2 model catalyst with well-defined interfaces, and electron transfer from Pd cubes to CeO2 nanorods through interfaces triggered CO oxidation at low temperature where standalone Pd and CeO2 are inert.

International audience; Ethylene oxide (EO) is industrially produced by epoxidation of ethylene on Ag-based heterogeneous catalysts. Electrophilic oxygen species are assumed to be active key species in the EO production. This study explores the possibility to electrochemically produced these oxygen species in a solid oxide electrochemical cell. Two series of Ag based cermet electrodes were prepared either with Yttria Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, or with Gadolinia-Doped Ceria (GDC), a mixed ionic and electronic conductor. Ag/YSZ cermet layers were deposited on planar and tubular YSZ dense substrates by using a conventional chemical method while Ag/GDC cermets were coated on GDC dense pellets by reactive magnetron sputtering. We evidenced a self-redispersion of Ag in the ethylene/oxygen mixture in Ag/YSZ cermet layers leading to the formation of small Ag clusters in close interaction with YSZ which are selective for epoxidation. However, the sintering process of these small Ag clusters is too fast even at 260°C to maintain the EO selectivity. On the other hand, the selectivity towards EO and the ethylene conversion of Ag/GDC cermet coatings were found to linearly increase with the applied current, demonstrating for the first time, the direct electrooxidation of ethylene into EO.

A novel catalyst design for electrochemical promotion of catalysis (EPOC) is proposed which overcomes the main bottlenecks that limit EPOC commercialization, i.e., the low dispersion and small surface area of metal catalysts. We have increased the surface area by using a porous composite electrode backbone made of (La0.8Sr0.2)0.95MnO3-δ/Ce0.9Gd0.1O1.95 (LSM/GDC). Highly dispersed Pt nanoparticles with an average diameter of 6.5nm have been deposited on LSM/GDC by atomic layer deposition (ALD). This novel design offers, for the first time, a controllable and reproducible method for the fabrication of EPOC catalysts. The bare electrode backbone shows negligible activity for propane oxidation, while in the presence of Pt nanoparticles a high catalytic activity is obtained above 200°C. The performance of the Pt-loaded LSM/GDC catalyst was significantly improved by application of small currents (I

A dynamic structural behavior of Pt nanoparticles on the ceria surface under reducing/oxidizing conditions was found at moderate temperatures ( H2>C3H6). This dynamic nature of Pt on ceria at such low temperatures (250–500 °C) was additionally confirmed by in situ environmental transmission electron microscopy. A general concept is proposed to adjust the noble metal dispersion (size, structure), for example, during operation of an exhaust gas catalyst.

International audience; Resistive soot sensors capable of measuring the mass concentration of particles in an exhaust pipe have been developed in a previous work. In particular, it has been shown that these sensors have an optimal sensitivity for a certain polarization voltage depending on the nature of the particles.This work shows that this effect can be explained by an equilibrium between the creation of soot bridges between the two collecting electrodes and their destruction initiated by Joule effect due to the polarization voltage. Based on this assumption, a model is proposed to predict the load curve (response versus time) of the sensor. In addition, the high frequency sampling of the sensor response has revealed some jumps of the sensor response (electrical conductance), which are exploited through a statistical approach to obtain additional information on the nature of the collected particles.

In this study, we have investigated, for the very first time, the oxygen electrode reactions on Ag/YSZ electrochemical catalysts both in oxygen and under reaction conditions compatible with the ethylene epoxidation reaction. Electrochemical Impedance Spectroscopy (EIS) in combination with in-situ Raman spectroscopy and catalytic activity measurements were used to identify and understand the main oxygen reaction pathways. The results obtained suggested that the rate limiting step under an O2 reaction atmosphere (at 300 °C) is the O2 adsorption/dissociation process on the Ag catalyst-electrode. In addition, the polarization resistance increased with time under the presence of O2. This was attributed to the formation of Ag2O on the catalyst surface or near surface, which limits the oxygen electrode reactions. Finally, we observed that the addition of ethylene in the feed stream hinders the electrode reaction, due to its competitive chemisorption with oxygen on Ag. These results give new insights into the design of selective Ag/YSZ catalyst for ethylene epoxidation. Keywords: Electrochemical Impedance Spectroscopy (EIS), Oxygen electrode reaction, Ag/YSZ, Ethylene epoxidation

The very close contact between ceria–zirconia and carbon soot allows the detection of oxygen transfer from ceria–zirconia to carbon by in situ Environmental HRTEM already at low temperatures. This highlights the outstanding redox behavior and soot oxidation potential of ceria–zirconia when suitable carbon–catalyst arrangements are generated at the nanoscale.

International audience; The preparation and characterization of pure fluorite-type phases allowed exploring the CeO2–ZrO2–PrOx (CZP) phase diagram. On the basis of magnetic susceptibility measurements, the Pr4+/Pr3+ molar ratio of several oxides annealed at T = 700 °C under air was determined; the higher the Zr content, the lower the Pr4+ concentration. Thermogravimetric analysis and temperature-programmed reduction measurements showed various Pr and Ce reduction steps. The Pr4+ reduction starts at T = 250 °C and is maximum around T = 400 °C. For the most reducible compositions, which exhibit the lowest Zr content and the highest Pr rate, the reduction phenomena strongly depend on the Pr/Ce molar ratio. As a remarkable result, Pr and Ce reductions can simultaneously take place at lower temperature (T > 430 °C) than for oxides of the CeO2–ZrO2 solid solution evidencing that the increase of Pr content also allows enhancing the reducibility of Ce4+ at low temperature. On the basis of a discussion taking into account the probability of oxygen surroundings in disordered fluorite networks and the rate of oxygen released in materials after the first reduction step performed at T < 500 °C, a mapping of the most probable labile oxygen sites in the CZP phase diagram is proposed. In particular, it is shown that for the oxides containing 10 atom % Zr, the most labile oxygen site should be systematically coordinated with one Zr atom, one Ce, and two Pr atoms. In the same series (10 atom % Zr), the electronic transport properties allowed showing semiconducting behavior with a strong increase of the total conductivity as the Pr content increases. On the basis of the thermal variation of the Seebeck coefficient, these phenomena are associated with hopping of electrons and holes, involving intra-atomic charge transfers, which depend on the reduction temperature of Pr4+ ions under air. Finally, the oxygen mobility strongly increases with the Pr content in this series. The oxygen tracer self-diffusion coefficient D* has been estimated by two independent measurements, and the best value is around 10–8 cm2/s at T = 400 °C for the Ce0.45Zr0.1Pr0.45O2–x composition, which is quite high in this temperature range. These fundamental properties of CZP phases design very promising new materials like automotive exhaust catalysts, gas sensors, electrolytes, or oxygen electrodes for solid oxide fuel cells.

During the last two decades the Electrochemical Promotion of Catalysis (EPOC) phenomenon has been studied extensively for many catalytic reactions including hydrocarbon oxidation reactions and hydrogenations. In the majority of the studies, the catalysts/electrodes consisted of porous noble metal films (Pt, Pd, Rh) prepared, for instance, by calcination of organometallic pastes. This results in low metal dispersion and low active surface area, limiting therefore the overall catalytic activity. In view of further practical application of the EPOC phenomenon to industrial catalysts, we should be able to enhance the activity of nanodispersed materials. In this study, for the very first time, we observed an enhanced catalytic activity of a Pd nanodispersed catalyst supported on a porous Co3O4 semiconductor film. The Pd/Co3O4 composite powder was deposited on an yttria-stabilized zirconia (YSZ) solid electrolyte without the presence of an interlayer film. The observed enhancement was non-Faradaic, with Faradaic efficiency values as high as 80. The Pd/Co3O4 catalyst was characterized thoroughly by means of a wide variety of physicochemical techniques, such as TEM, SEM, TGA, ICP and BET. In addition, this material was further compared with a classical Pd/YSZ metallic film, prepared by calcination of an organometallic paste. This allows for a comparison of metal-support interactions (MSI) and the EPOC effect. Using supported catalysts as catalytic films for electrochemical promotion studies may lead to the practical utilization of EPOC in the chemical industry or in gas exhaust treatment.