This study reports the electrochemical properties for NOx reduction of a ceria-based mixed ionic electronic conducting porous electrode promoted by Pt nanoparticles, as efficient catalyst for NO oxidation, and BaO, as sorbent to store NOx. This catalytic layer was deposited by screen-printing on a dense membrane of gadolinia-doped ceria, an O2− ionic conductor. The targeted Ba and Pt loadings were 150 and 5 μg/cm2, respectively. The NOx selective electrochemical reduction was performed between 400 °C and 500 °C with and without oxygen in the feed. Variations of the open-circuit voltage with time were found to be a good sensor of the NOx storage process on the ceria-based catalyst-electrode. However, no N2 production was observed in the presence of O2 phase in spite of nitrates formation.

This paper is a comprehensive study dealing with the parameters that influence the response of a resistive soot sensor which was developed for Diesel Particulate Filter (DPF) failure detection in a past project. From the conductance measurement between two Pt electrodes, and a regeneration strategy, this kind of sensor can provide the weight concentration of particulate matter (PM). In this study, we have characterized and determined the key parameters such as the PM distribution size and the polarization voltage between the electrodes that could influence the sensor response. First results show that the sensor response strongly depends on the polarization voltage applied between the two electrodes. (C) 2016 Elsevier B.V. All right reserved.

In this work, the origin of the Raman defects band at 570cm(-1) of praseodymium-doped ceria was revisited from in situ spectra using six different exciting lines between 458 and 785nm at low temperatures after oxidizing or reducing treatment. The observation of overtones and the fast change of relative intensity with excitation wavelength were explained by a resonance effect around 514nm, which involved a Pr4+ containing defect stabilized at the oxidized state leading to an absorption band around 530nm. The reduction of Pr4+ cations contained in such defects modifies the electronic properties of praseodymium doped ceria inhibiting the resonance effect. Additionally, the number of D1 defects that involved Pr3+ cations and oxygen vacancies increased allowing them to be distinguished. Copyright (c) 2016 John Wiley & Sons, Ltd.

1. Introduction Environmental regulations on NOx emissions of mobile sources are becoming increasingly demanding. The NOx storage-reduction (NSR) catalytic technology is one of the solution lean-burn engines. NSR catalysts work in cyclic gas-composition conditions. During the first step (lean phase), NSR materials store emitted NOx as nitrates until the surface reaches the saturation threshold. A pulse of fuel post-injection then triggers the short second step (rich phase), during which the reducing conditions lead to nitrate decomposition and release as well as subsequent NOx reduction into N2 and surface regeneration. Ceria is an interesting material since it plays a double function first as a high specific surface area support [1] for platinum group metal (PGM) dispersion and secondly as a NOx trap at low temperature until 350°C. Below 200°C, the NOx storage capacity of ceria is higher than that of barium which is commonly used as a storing agent [2]. In addition, ceria can limit the thermal sintering of Pt nanoparticles [3]. This study aims to deeply characterize the impact of the nature of dopant (Zr and Pr) on the redox properties of ceria-based oxides. 2. Experimental/methodology Different compositions of commercial ceria-based oxides were provided by the Solvay Special Chem Company : CeO2, Ce0.49Zr0.51O2 (CZ)) and Ce0,80Pr0,20O2 (CP20). All samples have been calcined at 800°C for 2 h. In-situ X-Ray Diffraction measurements were carried out in an atmosphere-controlled Anton Paar XRK 900 reactor chamber, either under air, N2 or H2, using a Versatile Panalytical X’Pert Pro MPD Diffractometer equipped with a diffracted beam graphite monochromator (Cu Kα radiation) and a 1-dimensional multistrip detector (X’Celerator). Diffractograms were collected at several temperatures from 25 to 750°C and crystallographic parameters were determined by the Rietveld method. Surface and bulk reducibility was characterized by Temperature-Programmed Reduction (TPR) in H2 from room temperature up to 850°C. Oxygen-Temperature-Programmed Desorption (TPD) experiments were also performed to quantify the surface reactivity of the different oxides toward oxygen. Oxygen was adsorbed at 500°C while the desorption was followed in He from RT up to 800°C with an heating ramp of 10°C/min. In-situ Raman spectroscopy was used to determine structural/electronic defects and surface oxygen species of the samples after reducing/oxidizing treatments. Spectra were recorded with a LabRam HR Raman spectrometer (Horiba-Jobin Yvon) at low temperature after oxidation or reduction at 525°C. Three exciting wavelengths were used (514, 633 and 785 nm) and the laser spot was focused using a ×50 long working distance objective. The in-situ Raman spectra were recorded using a THMS600 cell (Linkam) between -196°C and 525°C under 10 % H2-N2, N2 and 10% O2-N2. 3. Results and discussion XRD patterns have evidenced the cubic structure (Fm-3m) for CeO2 and CP20 while CZ also contains a t’ tetragonal phase. The lattice parameters were extracted from in-situ patterns in air, N2 and H2 as a function of the temperature. The increase of the lattice parameter with respect to the one measured in air at a given temperature was used to estimate the bulk reducibility. Figure 1a clearly shows that CP20 is reduced in pure H2 from 300°C, instead of 400°C for CZ and above 700°C for CeO2. These results are in good agreement with TPR experiments which evidenced that the surface reduction of doped ceria is promoted by the insertion of Pr. By the same way during O2-TPD experiments, a low O2 desorption peak below 400°C was only observed on CP20. In addition, the capacity of the ceria oxide to chemisorb oxygen was strongly improved in the presence of Pr. Beyond confirming the XRD structural characterization, Raman mappings evidenced a high homogeneity at the micrometer scale. Furthermore, structural defects and oxygen species were observed with this technique. In particular, Raman spectra of CP20 oxide highlighted a defects band at 570 cm-1 (Figure 1B) which can be explained by a resonance effect involving a particular defect stabilized at the oxidized state. The reduction of cations contained in such defect modifies its electronic properties inhibiting the resonance effect. Concerning CZ support, a typical band of Ce3+ was visible after reduction whereas peroxo species were observed after re-oxydation contrarily to the other solids. Figure 1. (A) Variation of the fluorite lattice parameter as a function of temperature in pure H2 (B) Evidence of a new defects band enhanced by Raman Resonance effect for CP20. 4. Conclusion Structure, surface and bulk properties of three different ceria oxides have been deeply investigated in both oxidized and reduced states. The role of the dopants, i.e. Pr and Zr, on the redox properties in cycling lean/rich conditions encountered in NSR processes will be discussed. 5. References [1] Z. Say, E.I. Vovk, V.I. Bukhtiyarov, E. Ozensoy, Appl. Catal. B Environ. 142-143 (2013) 89–100. [2] E. Rohart, V. Belliere-Baca, K. Yokota, V. Harle, C. Pitois, Top. Catal. 42-43 (2007) 71–75. [3] Y. Nagai, T. Hirabayashi, K. Dohmae, N. Takagi, T. Minami, H. Shinjoh, S. Matsumoto, J. Catal. 242 (2006) 103–109.

The NO x (mainly NO and NO 2 ) pollutions that come from the exhaust of the thermal engines can give rise to a serious threat to the environment and human health. The design of more efficient and stable catalysts to reduce NO x to nitrogen in atmospheres containing excess oxygen (typically, from exhaust gas emitted by diesel and lean-burn gasoline engines) has attracted so much attention in the last years. The two actual technologies are using an additional reducing agent to remove NOx, i.e. Diesel fuel post-injection for the NOx storage reduction process and urea for the selective catalytic reduction. An alternative solution could be the electrochemical reduction of NOx in solid oxide electrolysis cell (SOEC) [1,2] that can save the huge reducing agents storage system. This study reports the electrochemical properties for NO x reduction of a Mixed Ionic Electronic Conducting (MIEC) porous electrode promoted by Pt nanoparticles, as efficient catalyst for oxidation reactions, and BaO, as sorbents to store NO x . Pt and BaO nanoparticles were finely dispersed in the porosity of a MIEC film, based on a composite between LSCF (La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3-δ ) and GDC (Gd 0.2 Ce 0.8 O 1.9 ), which was deposited using screen-printing. This catalytic layer was interfaced on a dense pellet of gadolinium doped ceria (GDC), an O 2- ionic conductor. The Ba and Pt loadings were around and 150 and 5 µg/cm², respectively. The catalytic performances, upon positive and negative polarizations, have been measured as a function of temperature in the range 200°C-500°C, partial pressure of oxygen and in the presence of propene in the feed. The NO x electrochemical conversion into N 2 was found to be driven by the current (Figure 1) and the catalytic activity of the electrode for NO oxidation. In parallel, electrochemical properties have been carried out by using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the electrocatalytic mechanism. Finally, the Pt and BaO nanoparticles in the LSCF/GDC film were characterized by transmission electronic microscopy. References T.J. Huang, C.Y. Wu, S.H. Hsu, C.C. Wu, Energy Environ. Sci. , 4 , 4061 (2011). R. M. L. Werchmeister, J. J. Bentzen, K. B. Andersen, and K. Kammer Hansen, J. Electrochem. Soc. , 161(10) H663-H669 (2014) Figure 1

The NOx (mainly NO and NO2) pollutions that come from the exhaust of the thermal engines can give rise to a serious threat to the environment and human health. The design of more efficient and stable catalysts to reduce NOx to nitrogen in atmospheres containing excess oxygen (typically, from exhaust gas emitted by diesel and lean-burn gasoline engines) has attracted so much attention in the last years. The two actual technologies are using an additional reducing agent to remove NOx, i.e. Diesel fuel post-injection for the NOx storage reduction process and urea for the selective catalytic reduction. An alternative solution could be the electrochemical reduction of NOx in solid oxide electrolysis cell (SOEC)[1,2]that can save the huge reducing agents storage system. This study reports the electrochemical properties for NOx reduction of a Mixed Ionic Electronic Conducting (MIEC) porous electrode promoted by Pt nanoparticles, as efficient catalyst for oxidation reactions, and BaO, as sorbents to store NOx. Pt and BaO nanoparticles were finely dispersed in the porosity of a MIEC film, based on a composite between LSCF (La0.6Sr0.4Co0.8Fe0.2O3-δ) and GDC (Gd0.2Ce0.8O1.9), which was deposited using screen-printing. This catalytic layer was interfaced on a dense pellet of gadolinium doped ceria (GDC), an O2- ionic conductor. The Ba and Pt loadings were around and 150 and 5 µg/cm², respectively. The catalytic performances, upon positive and negative polarizations, have been measured as a function of temperature in the range 200°C-500°C, partial pressure of oxygen and in the presence of propene in the feed. The NOx electrochemical conversion into N2 was found to be driven by the current (Figure 1) and the catalytic activity of the electrode for NO oxidation. In parallel, electrochemical properties have been carried out by using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the electrocatalytic mechanism. Finally, the Pt and BaO nanoparticles in the LSCF/GDC film were characterized by transmission electronic microscopy. References T.J. Huang, C.Y. Wu, S.H. Hsu, C.C. Wu, Energy Environ. Sci., 4, 4061 (2011). R. M. L. Werchmeister, J. J. Bentzen, K. B. Andersen, and K. Kammer Hansen, J. Electrochem. Soc., 161(10) H663-H669 (2014) Figure 1

The modification of a HY zeolite (with Si/Al ratio = 2.5) by impregnation with a platinum salt or ion exchange with Cu2+ cations was carried out in order to evaluate the potential interest of the obtained materials as hydrocarbon traps for cold-start application. Textural, structural and chemical characterizations were carried out using N-2 adsorption isotherms at -196 degrees C, XRD and DRIFTS of adsorbed CO and NO. Acidic properties of the parent H/Y and Cu- and Pt-modified zeolites were determined using FTIR of adsorbed pyridine. The methodology used to investigate the adsorption behaviour of the parent and modified HY zeolites consisted in: (i) analysing qualitatively and quantitatively the breakthrough curves obtained at 35 degrees C during the adsorption of a ternary hydrocarbon mixture (propene, toluene, decane) as well as the data from subsequent temperature-programmed experiments (TPD under He or TPSR in presence of 10%O-2 or 10%O-2/0.2%NO) (ii) establishing relationships between adsorption/reactivity data and the structural, textural and chemical properties of the modified zeolites. Namely, the introduction of copper and platinum species considerably improves the adsorption of unsaturated hydrocarbons, such as propene or toluene, at the expense of decane. This results in a more adequate balance between all the hydrocarbons adsorbed, which is required for cold-start application. In addition, Cu/Y and Pt/Y zeolites were also found to be efficient for the removal of NOx or HC total oxidation, respectively. (C) 2016 Elsevier Inc. All rights reserved.

Adsorption behavior of commercial zeolites were investigated for the trapping of a hydrocarbon mixture (propene, toluene and decane) mimicking Diesel cold start exhausts under dry conditions. The studied commercial zeolites, in most cases under protonated form, (with Si/Al ratio in the range 2-15) present different structures: FAU, *BEA, MOR, MFI, FER, and LTA. Textural and structural characterizations were carried out using N-2 adsorption at-196 degrees C and X-ray diffraction. In situ FTIR spectroscopy of adsorbed pyridine was used to probe quantitatively the acid sites. The methodology used in this study consisted of an adsorption phase at 35 degrees C followed by temperature-programmed desorption (TPD) under He at 10 degrees C/min, and three different adsorption mechanisms were highlighted according to the pore size and the host framework. MOR and MFI structures appear to be the less selective for any type of hydrocarbon and are thus the most suitable for cold start applications. Except for these types of zeolites presenting a "single-file diffusion" mechanism, propene often desorbs at low temperatures or is adsorbed very little. By contrast, heavier hydrocarbons such as toluene and decane desorb at temperatures that match with three-way catalyst (TWC) or Diesel oxidation catalyst (DOC) light-off temperatures.

The behavior of 5%Ni-wt.-impregnated and 5%Ni-wt.-15%Ce-wt.-impregnated zeolites (of USY type) were investigated by in situ/operando IR spectroscopy, both for CO2 adsorption and under methanation conditions (H-2:CO2/4:1) reaction. In situ FTIR and CO2-TPD experiments highlighted that CO2 adsorption is rather poor over NiUSY zeolite, whereas CO2 uptake over CeNiUSY leads to the formation of a large amount of adsorbed carbonates on the CeO2 surface. Mechanistic pathways involved in CO2 methanation over CeNiUSY catalyst are discussed in accordance with infrared spectroscopic data. Under methanation conditions, hydrogen is dissociated on Ni degrees particles and reacts with hydrogen and bidentate carbonates, leading first to the formation of monodentate formates, and then to methane, by further hydrogenation. No adsorbed carbonyls onto Ni were detected while a large amount of formates was highlighted from 150 degrees C. The formate decomposition appears to be a kinetic relevant step to the observed kinetics of the CO2 hydrogenation reaction. (C) 2016 Elsevier B.V. All rights reserved.

Ni-impregnated USY zeolites with increasing Ni content (5, 10, 14%(wt).) were investigated by operando IR spectroscopy for both CO2 adsorption and CO2 methanation conditions reaction. In-situ FTIR and TPD experiments highlighted a rather weak CO2 adsorption, which occurs namely as carbonates or CO2 linear complexes over cations (e.g., Na+). Under methanation conditions, dissociated hydrogen reacts with carbonates and/or physisorbed CO2, leading to monodentate formates, then carbonyls (both adsorbed onto Ni-0 particles), and finally to methane. A detailed mechanism of the pathways involved in CO2 methanation over NiUSY catalysts is then discussed in accordance with infrared spectroscopic data. (C) 2015 Elsevier B.V. All rights reserved.

In this work, CO2 methanation reaction was studied on Ni-based zeolite catalysts, which were prepared by incipient wetness impregnation of USY zeolite with 5 wt% Ni. The effects of the drying method after impregnation, the calcination temperature and the pre-reduction temperature on the catalysts performances were evaluated. The catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction, diffuse reflectance UV–Vis spectroscopy (DRS UV–Vis), transmission electron microscopy and X-ray diffraction. Drying under microwaves irradiation induced remarkable changes on the type, location and reducibility of Ni species at the same time that leaded to effects in the structural and textural properties of the support and in the average nickel particle size. As a result, changes in the catalytic performances were observed. The calcination temperature changed the location and reducibility of the Ni species being concluded that calcining at 300 °C leads to higher conversions and selectivities. At high reduction temperatures the amount of reduced Ni species (active sites) was greater, but the impact of sintering processes was also stronger. For catalysts with 5 % Ni, the reduction at 550 °C was observed as the most favourable. However for 14 % Ni sample no remarkable effects were observed by reducing at higher temperatures. Thus, it was proved that CO2 conversion and CH4 selectivity can be maximised through the proper choice of both preparation and pre-reduction conditions.

Adsorption behavior of a hydrocarbon mixture (propene, toluene, decane) mimicking Diesel cold-start was investigated under dry and wet conditions for commercial HY zeolites with a Si/Al ratio ranging from 2.5 to 100. Textural and structural characterizations were carried out using N-2 adsorption at 77 K and X-ray diffraction. In situ FTIR spectroscopy of adsorbed pyridine was exploited to probe acidic sites. The methodology used in this study consisted of adsorption phase at 35 degrees C with several kinds of mixtures followed by a Temperature-Programmed Desorption (TPD) at 10 degrees C/min. At high Si/Al ratio, a competitive thermodynamic adsorption between toluene and decane was demonstrated. To the opposite, propene is substantially not adsorbed whatever the Si/Al ratio of the zeolite. By decreasing the Si/Al ratio, the presence of large amounts of acidic sites enhances adsorption of unsaturated hydrocarbons. Water adsorption was found to be detrimental for HC storage due to hydrophilic nature.

The general purpose of this work is to examine the relative ability of some well-selected zeolitic materials for the reduction of HC emissions generated within the Diesel "cold-start" period, i.e. when the work temperature of the Diesel Oxidation Catalyst (DOC) has not been reached. More peculiarly, this study is focused on the chemical, textural and structural parameters of zeolites influent on the elimination, namely by adsorption, of unburnt HC (propene, toluene and decane) in presence of potential inhibitors (H2O, CO, NO). Simulated "cold-start" conditions consisted in the rapid heating of the pre-treated zeolite sorbent/catalyst under the whole gas mixture from 35 to 530 C. The quantity of trapped HC and those converted to CO, by oxidation were measured in function of the temperature, as well as the amount of NOx converted by the HC-SCR reaction. The interpretation of the HC emission profiles in close relation with the porous and acidic (through FTIR of adsorbed pyridine) properties of the corresponding zeolites allowed to gain insight onto the relative contributions of the pore topology, the pore size and the acid strength. For some selected zeolites, several consecutive cold-start cycles were performed in order to assess their stability. (C) 2014 Elsevier B.V. All rights reserved.

AbstractThe effect of water on NOx storage performance of a Pt/BaO/Al2O3 catalyst was investigated. The adsorption capacity of a model NOx storage‐reduction system (NSR) catalyst was studied in the presence of NO, oxygen, and water in nitrogen. Fixed‐bed and in situ DRIFTS adsorption tests were carried out in order to evaluate the influence of water on the adsorption capacity of the catalyst, adsorbed species on the surface of the catalyst, and stability of these species. The presence of water slightly reduces the NOx storage capacity of the NSR catalyst. A decrease of platinum oxidation activity was observed which was correlated to a slowdown of surface bidentate nitrate formation, detected by in situ DRIFTS tests. On the other hand, surface monodentate nitrates were favored and formation of bulk nitrates was not affected. A set of reactions corresponding to these observations is proposed.

The influence of the presence of H2O on the contact between carbon, used as model soot, and a model four-way catalyst (1% Pt-10% BaO/Al2O3) was investigated. NOx adsorption/TPD cycles at 300 degrees C together with XRD, XPS and DRIFTS characterizations showed that only surface nitrate species are destabilized by the carbon present in the catalytic bed, leading to a decrease of the NOx storage capacity and carbonate species formation. In another way, injection of water in the reactive gas flow decreases also the NOx storage capacity of the catalyst, but promotes the formation of stable nitrate species. A non-cumulative effect of carbon and water was observed. It was proposed that a competition between the destabilization, by carbon, of weakly bonded surface nitrate species and the enhancement of bulk nitrate species formation in the presence of water occurs. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Silver species present in four different Ag-based catalysts, with different supports (Al2O3, ceria-zirconia, sulphated ceria-zirconia and MFI zeolite), were identified by a combination of different characterization techniques (Powder XRD, Raman Spectroscopy, TEM, H-2-TPR, DRS UV-Vis Spectroscopy, CO adsorption followed by DRIFTS and pyridine adsorption followed by FTIR), each one allowing to obtain information on specific Ag species. While Powder XRD and Raman gave structural information on the Ag species present on the catalysts, complementary information on their relative reducibility and electronic state was obtained by H-2-TPR, DRS UV-Vis and CO adsorption followed by DRIFTS.The possibility of different redox cycles occurring during the NOx SCR reaction between the silver species present in each catalyst was discussed. (C) 2013 Elsevier B.V. All rights reserved.