Síntese e caracterização de catalisadores obtidos a partir de materiais com estruturas do tipo φ

• Autor(a) principal: Santos, Letícia Pagotto dos
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12062
• topic: 𝚽z and 𝚽y Structures; Llayered structures; Vanadium; Molybdenum; Niobium; Estruturas 𝚽z e 𝚽y; Estruturas lamelares; Vanádio; Molibdênio; Nióbio; Síntese; CNPQ::ENGENHARIAS::ENGENHARIA QUIMICA::TECNOLOGIA QUIMICA

𝚽 type compounds has layered structures consisting of two divalent transition metals and another hexavalent or pentavalent, being possible to replace them totally or partially. The objective of this study was to synthesize and characterize the catalysts obtained from precursors with 𝚽 type structures, replacing partially by Mo, V and Nb the position of penta / hexavalent metal, using Zn as a divalent metal. To analyze the effect of heavy metals, the percentage (of these only) was varied, with Mo 19 to 81%, V 14 to 95% and Nb 5 to 15%. The synthesis method used was the co-precipitation, and also hydrothermal for Mo81V14Nb5 precursor. The technique of characterization by X-ray diffraction confirmed that the synthesized precursors have the 𝚽z type structure, except for the material with 81% Mo (Mo81V14Nb5), which has the 𝚽y type structure. The molar fraction of the respective metals on the precursors was determined from the results of XRF analysis, which showed that Mo was incorporated only in the precursor structure with most of the metal composition (81%) and a greater tendency to form 𝚽y phase. In the thermogravimetric analysis mass loss of about 15% for all precursors to 550 °C was determined and infrared Fourier transform been observed characteristic bands of V-O, Zn-O and Mo-O bonds. The catalysts were obtained by calcining the precursor at 550 and 750 °C, and the catalyst that has 95% V and 5% Nb (V95Nb5C550) which has high specific area. The identification by X-ray diffraction of the catalysts showed the formation of 𝚽-ZnMoO4 and Zn3Mo2O9 mixed oxide catalysts in the coming 𝚽y phase; ZnO, ZnV2O4 and Zn(V0,12Nb0,88)2O6 oxides for the V95Nb5C550 and V90Nb10C550 catalysts, and 𝚽-ZnV3O8 and Zn3V2O8 to the other catalysts. Raman spectroscopy was observed tetrahedral coordination of characteristic bands of the vanadate ion (VO43-), and also related to tetrahedral coordination ion molybdate (MoO42-). The catalyst with 95% V and 5% Nb calcined at 750 °C exhibited the best reactivity in the methane steam reforming reaction, with formation of products from 400 °C