Papers by Author: Jean R. Gavarri

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Authors: José Cosme Cunha Gomes, C.P. Souza, Uilame Umbelino Gomes, Jean R. Gavarri, Jean P. Dallas, C. Leroux
Abstract: Rare earth oxides have been widely investigated in catalysis as structured and electronic promoters to improve the activity and thermal stability of catalysts. Cerium has an important role in three-way catalysis and fluid catalytic cracking, two significant catalytic processes by their economic relevance and tonnage. Cerium and other rare earths have been studied as possible heterogeneous catalysts at selective oxidation of hydrocarbons. Cerite and monazite are minerals with high concentration of cerium element. Extraction of cerium metal using conventional leaching processes has shown low yields or high costs. The main purpose of this research work is to optimize the parameters in cerium purification stage from this mineral using leaching process. To separate particles with different granulometries, the mineral is ground and fractioned with sieves of 80, 200, 250 and 400 mesh. In order to put off organic components and oxidize cerium(III) to cerium(IV), samples were roasted at 1073K by twenty-four hours. The roasted samples were solubilized by acid attack (leaching) for approximately twenty-four hours; according to the acid used hydrochloric or sulfuric), cerium and other trivalent elements are solubilized as chloride or sulfate solution. Cerium was extracted by selective precipitation at pH~3,4 using ammonium or natrium hydroxide as pH changer. After filtration and drying, the precipitated product was characterized by XRD (x-ray diffraction), and then process efficiency was determined (cerium percentage and the different phases in the powder). Particles granulometry, roasting process (time and temperature), as well as leaching parameters (acid used, time, temperature and concentration of reagents) were the main variables studied.
Authors: S. Saitzek, Sylvie Villain, Jean R. Gavarri
Abstract: In the general framework of studies on nanomaterials for micro-sensors, cerium dioxide nanopowders (CeO2-z) and nanocomposites systems of copper doped ceria (CuOx-CeO2-z) were prepared and characterized. The aim of this specific study is to try to connect catalytic activity of such nanopowders with microstructure, additional phases and/or doping effect. The nanopowders of pure and doped cerium oxide were elaborated from various “Sol-Gel” chemical routes. Microstructural analysis was first carried out by X-ray diffraction (XRD). The specific areas were determined from BET adsorption techniques and the results were correlated to the size determinations obtained from XRD. The catalytic activity of such nanopowders in presence of methane gas CH4 was analyzed making use of FTIR spectrometry and a homemade device. For a better understanding of such catalytic responses, we proposed a modeling approach of solid gas interactions that takes into account a typical temperature dependent Avrami's model.
Authors: Sylvie Villain, C. Leroux, Jean Musso, Jean R. Gavarri, Agnes Kopia, Magdalena Klimczak, J. Kusinski
Authors: M. Chmielowska, Agnes Kopia, C. Leroux, S. Saitzek, J. Kusinski, Jean R. Gavarri
Abstract: The structural analysis of thin cerium dioxide films doped with Cu, produced by laser ablation for applications in catalytic and gas sensors, was the general aim of the study. The thin films deposited on a (100) silicon substrate were nanocrystalline structure with a well-developed texture. The morphology, as well as the preferred films orientation, is changed with the volume fraction of Cu. The observed changes affect the catalytic properties of the materials obtained which was confirmed by the catalytic tests undertaken with CH4.
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