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Previous issue date: 2017-07-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Esse trabalho prop?s uma rota alternativa de s?ntese de catalisadores para rea??es de oxida??o do metanol e etanol a serem aplicados em c?lulas a combust?vel, sendo estes a base de ?xidos e precursores mistos de ni?bio e t?ntalo puros e dopados com cobalto, cobre e n?quel, obtidos a partir do mineral de base, a columbita/tantalita. Inicialmente, foi efetivado um planejamento experimental da purifica??o total deste min?rio, na sequ?ncia, foi realizada a dopagem usando um percentual de 10%, em massa. Os tratamentos t?rmicos foram realizados em tr?s diferentes temperaturas (110, 400 e 600 ?C). Na sequ?ncia, foi efetivada a s?ntese do precursor oxalato, que foi utilizado, por conseguinte, na s?ntese dos precursores dopados onde estes passaram pelos mesmos procedimentos dos ?xidos. O min?rio puro e tratado foi caracterizado por fluoresc?ncia de raios X (FRX) e difra??o de raios X (DRX) que mostraram a sua total purifica??o. O precursor foi avaliado atrav?s das an?lises de difra??o de raios X (DRX), espectroscopia de infravermelho (IV), an?lises t?rmicas (TG/DTG/DSC e DTA) e a microscopia eletr?nica de varredura (MEV); apresentando part?culas inferiores a 0,2 micrometros, um alto valor de perda de massa (76,6 %) e uma estrutura porosa de formas irregulares. Os catalisadores puros e dopados foram submetidos ?s an?lises por difra??o de raios X (DRX), espectroscopia de fotoel?trons excitados por raios X (XPS), microscopia eletr?nica de varredura (MEV) e microscopia eletr?nica de transmiss?o (MET), que apresentaram fortes ind?cios de propriedades catal?ticas para a oxida??o devido a sua r?pida redu??o. Na caracteriza??o el?trica, estes catalisadores foram avaliados pela t?cnica da voltametria de pulso diferencial (DPV) atrav?s de sensores em rea??o para a oxida??o dos ?lcoois. As an?lises demonstraram que estes materiais s?o ?timos condutores, porque aumentaram a passagem de corrente el?trica do eletrodo de trabalho em at? duas ordens de grandeza superior ao eletrodo de ouro. Os melhores desempenhos para as rea??es foram observados principalmente com o dopante de cobre, seguido por o n?quel, o puro e depois o de cobalto, considerando ainda que os materiais obtidos possuem caracter?sticas apropriadas para aplica??o em eletrodos de c?lulas a combust?vel. / This paper proposes an alternative route for producing catalysts for methanol and ethanol oxidation reactions to be applied on fuel cells. Those catalysts are based on oxides and precursors of mixed niobium and tantalum materials in their pure and doped (with Co, Cu or Ni) forms. These materials are obtained from columbite/tantalite, which is the base mineral for Nb, Ta. At first, an experimental planning for the complete purification of the mineral was performed. After purification, 10%wt. doping with each of the metals, and thermal treatment at three different temperatures (110,400 and 600?C) was carried out. Un-doped purified oxides were then subject to complexation process followed by metal addition (doping) and thermal treatment. Purified and thermally treated mineral was characterized by X-Ray Fluorescence (XRF) and X-Ray Diffraction and complete purification was attained. Complex precursors were evaluated on the basis of XRD, Infra-Red Spectroscopy (IR), thermal behavior (TG/DSC and DTA) and morphology (Scanning Electron Microscopy) and presented particle sizes under 0.2 ?m, elevated weight loss (76.6%) and a porous structure of irregular shape. Pure and doped catalysts were characterized on XRD, XPS (X-Ray Excited Photon Spectroscopy), SEM and TEM (Transmission Electron Microscopy) basis, presenting indication of catalytic properties interesting for oxidation reactions, such as quick surface reduction. Electrical evaluation of the catalysts was performed according to Differentia Pulse Voltammetry (DPV) with the use of micro sensors during alcohol oxidation reactions. These analyses indicated the excellent conducting characteristics of the materials as electric current flow was increased in two orders of magnitudes in comparison to gold electrodes. The best catalytic behaviors were observed when dopping was performed with copper, followed by nickel, without and cobalt dopant addition. Therefore, the synthesized materials presented characteristics that indicate their suitability for use as fuel cells electrodes.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/24350 |
| Date | 31 July 2017 |
| Creators | Barbosa, Cleonilson Mafra |
| Contributors | 13681389420, Oliveira, Ana Karla Costa de, 02293566480, Silva, Ariadne de Souza, 00735940401, Penha, F?bio Garcia, 68001851915, Gomes, Uilame Umbelino, Souza, Carlson Pereira de |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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