Navegando por Autor "Alencar, Lorena Dariane da Silva"

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    Effect of different synthesis methods on the textural properties of calcium tungstate (CaWO4 ) and Its catalytic properties in the toluene oxidation.
    (2018) Alencar, Lorena Dariane da Silva; Lima, Naiara Arantes; Mesquita, Alexandre; Probst, Luiz Fernando Dias; Batalha, Daniel Carreira; Rosmaninho, Marcelo Gonçalves; Fajardo, Humberto Vieira; Bernardi, Maria Inês Basso
    Calcium tungstate (CaWO4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FE-SEM images showed particles with rounded morphology and particles in clusters dumbbells-like shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples.
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    Preparation, characterization and catalytic application of Barium molybdate (BaMoO4) and Barium tungstate (BaWO4) in the gas-phase oxidation of toluene.
    (2017) Alencar, Lorena Dariane da Silva; Mesquita, Alexandre; Feitosa, Carlos Alberto Carneiro; Balzer, Rosana; Probst, Luiz Fernando Dias; Batalha, Daniel Carreira; Rosmaninho, Marcelo Gonçalves; Fajardo, Humberto Vieira; Bernardi, Maria Inês Basso
    Barium molybdate and Barium tungstate are important materials due their photoluminescent properties and they also have catalysis and photocatalysis applications. In this work, powders of these compounds were prepared by microwave-assisted hydrothermal (MAH) method and polymeric precursor method (PPM) and their structural and optical properties were studied. Furthermore, these materials were employed as solid catalysts towards gas phase toluene oxidation reactions. X-ray diffraction confirms the purity of materials at both preparation methods and reveals a preferential growth when the powders are prepared by MAH due polymeric agents and processing using microwave, which was confirmed by Field emission scanning electron microscopy. Photoluminesce emission was attributed to the charge-transfer transitions within the [WO4]2- and [MoO4]2- complexes. The H2 Temperature-Programmed Reduction (H2-TPR), O2-chemisorption and extended X-ray absorption fine structure (EXAFS) results indicated that BaWO4 samples, compared with BaMoO4 samples, have higher oxygen mobility and oxygen vacancies that appear as key factors for the achievement of better catalytic performances.