Synthesis and application of perovskite materials used in electrochemical promotion of VOCs catalytic combustion

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Molten salt synthesis of lanthanum cuprate, La2CuO4+ (delta)

Matei, Cristian Berger, Daniela Marote, Pedro Deloume, Jean-Pierre Sp. Iss. SILanthanum cuprate (LCO) was synthesized from lanthanum and copper precursors in molten sodium nitrate-potassium nitrate eutectic. The chemical reactions were studied by thermogravimetric analysis and X-ray powder diffraction was used to identify the crystalline phases. The chemical reactions of copper and lanthanum precursors in alkaline nitrate eutectic were studied and the basicity of the reaction mixture was increased in order to precipitate the crystalline mixed oxide. Scanning electron microscopy investigation has shown the obtaining of lanthanum cuprate as large platelet crystals of quadratic shape. The synthesis conditions are favourable for a direct formation of a superoxygenated lanthanum cuprate, La2CuO4 + (delta)

Study of oxygen desorption from doped lanthanum cobaltites: new possibilities through fast intermittent temperature-programmed desorption

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Intermittent temperature-programmed desorption study of perovskites used for catalytic purposes

International audienceA differential desorption technique, called intermittent temperature-programmed desorption (ITPD), was used to give new insights into the properties of La1−xSrxCo0.8Fe0.2O3 perovskites as a contribution to improve their performances with respect to various important application fields such as catalysis, electrocatalysis and solid oxide fuel cells (SOFC). Both ITPD and interrupted TPD (carried out at different heating rates) evidenced two distinct oxygen adsorbed states, desorbing at temperatures lower than 400 °C, corresponding to less than 5% of a compact monolayer of oxide ions. The first one, for low desorption temperatures (lower than 290 °C) exhibits a heat of adsorption (ΔH) distribution from 101 to 121 kJ mol−1. The second one, for higher desorption temperatures (between 290 and 400 °C) corresponds to ΔH = 146 ± 4 kJ mol−1. Additionally, for temperatures higher than 400 °C, we observed a continuous desorption of oxygen species, probably originating from the sub-surface or semi-bulk, with an associated activation energy of desorption ≥175 kJ mol−1

Catalytic combustion of toluene over a Sr and Fe substituted LaCoO3 perovskite

International audienceA series of La1 − xSrxCo1 − yFeyO3 (LSCF) perovskite catalysts was synthesized by a combined citrate–EDTA complexing method. The powders obtained were characterized by XRD, N2 adsorption and O2-TPD. After comparing the activities of the LSCF catalysts for the catalytic combustion of toluene, it was found that the substitution by little amounts of Sr and Fe improved the activity of LaCoO3. Such improvement can be explained by the increased amount of weakly adsorbed oxygen, evidenced by O2-TPD profiles

Lanthanum-based perovskites obtained in molten nitrates or nitrites

International audienceLanthanum-based perovskites, LaMO3 (where M = Mn, Fe, Co, Ni), have been synthesised from lanthanum precursors and corresponding 3d transition metal salts in molten alkali metal nitrates or nitrites. The reactivity of eight precursors in three molten salts of different basicity was analysed. Single phase orthorhombic LaMnO3.11, and orthorhombic LaFeO3 have been obtained in molten NaNO2 at 723 K, for 2 h. LaCoO3 is also formed in molten nitrite, but an increase of basicity, by adding Na2O2, was necessary to obtain LaNiO3. The reaction systems were investigated by thermal analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and specific surface area measurements (BET method) were used to characterise the synthesised nanopowders

Study of oxygen desorption from substituted perovskites: New possibilities through fast intermittent temperature-programmed desorption

International audienceA differential desorption technique, named intermittent temperature-programmed desorption (ITPD), has been used to get new insights into the properties of La1 − xSrxCo0.8Fe0.2O3 − δ perovskites. The apparent activation energy of desorption (Eapp) and the frequency factor (ν) were calculated from ITPD data, for the two distinct oxygen species desorbing from perovskite at temperatures lower than 400 °C. The low values (about 107–108 s−1) obtained for νapp indicated that re-adsorption occurred during the TPD process and therefore that Eapp is equal to the Heat of adsorption (E=−ΔH). The first oxygen species, related to lower desorption temperatures, exhibits a distribution of E from 105 to 125 kJ mol−1. The second one, related to higher desorption temperatures, corresponds to E=146±4 kJ mol−1 and 139±5 kJ mol−1, for x=0.2 and x=0.3, respectively. The relative amounts of these species contributing to the desorption peak are dependent upon Sr content in the perovskite

Synthesis and application of perovskite materials used in electrochemical promotion of VOCs catalytic combustion

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Oxygen mobility in lanthanum nickelate catalysts for deep oxidation of propane

Boreave, Antoinette Tan, Huili Roche, Virginie Vernoux, Philippe Deloume, Jean-Pierre 16th International Conference on Solid State Ionics JUL 01-06, 2007 Shanghai, PEOPLES R CHINANickelate catalysts were prepared by a modified Pechini method. Single phases of La2NiO4 (LN) and La1.9Sr0.1NiO4 (LSN) were obtained after calcination at 1000 degrees C in air. O-2-temperature-programmed desorption (TPD-O-2) experiments have shown that, in spite of quite small specific area, this material exhibits extremely high bulk oxygen mobility since interstitial oxygen species can be exchanged with the gas phase at temperatures as low as 230 degrees C. Furthermore, these oxygen species can react with propane to mainly form CO2 from 300 degrees C. (c) 2008 Elsevier B.V. All rights reserved

La(1-x)SrxCo1-yFeyO3 perovskites prepared by sol-gel method: Characterization and relationships with catalytic properties for total oxidation of toluene

Rousseau, S. Loridant, S. Delichere, P. Boreave, A. Deloume, J. P. Vernoux, P.La(1-x)SrxCo(1-y)FeyO3 samples have been prepared by sol-gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co3O4 that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 degrees C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La3+ by Sr2+ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La0.7Sr0.3Co0.8Fe0.2O3. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mossbauer spectroscopy. Cobalt oxidation states and the amount of O- electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La3+ by Sr2+. The strong lowering of the temperature at conversion 20% for the La0.7Sr0.3Co(1-y)FeyO3 samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O- electrophilic species for the La0.7Sr0.3Co(1-y)FeyO3 samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O- species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn-Teller effect and Mossbauer spectroscopy evidenced the presence of Fe4+ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La0.7Sr0.3Co0.8Fe0.2O3 sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co3O4 particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co3O4. (C) 2008 Elsevier B.V. All rights reserved