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Previous issue date: 2014-11-06 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / Esta tese ? parte de pesquisa sobre novos materiais para catalisadores e
sensores de g?s mais ativos, sens?veis, e seletivos. O objetivo desta tese foi desenvolver
e caracterizar ferrita de cobalto em diferentes morfologias, a fim de estudar sua
influ?ncia sobre a resposta el?trica e a atividade catal?tica do material. Foi tamb?m de
hierarquizar estes nanocristalitos para obter maior difusividade do g?s no material. Os
p?s foram produzidos via hidrot?rmica e solvot?rmica, e foram caracterizados por
termogravimetria, difra??o de raios X, microscopia eletr?nica de varredura, microscopia
eletr?nica de transmiss?o (difra??o de el?trons, simula??es de alta resolu??o), e
espectroscopia de energia dispersiva. As propriedades catal?ticas e el?tricas foram
testados em presen?a dos gases CO e NO2, este ?ltimo em diferentes concentra??es (1-
100 ppm), e a diferentes temperaturas (temperatura ambiente at? 350 ?C).
Nanooctaedros com tamanho m?dio de 20 nm foram obtidos por via hidrot?rmica.
Determinou-se que a forma dos cristalitos est? principalmente associada ? natureza do
agente precipitante e ? presen?a de ?ons OHno
meio de rea??o. Por via solvot?rmico,
foram preparados p?s esf?ricos de CoFe2O4 e com tamanho de cristalitos de 8 e 20 nm.
Os p?s de CoFe2O4 apresentam uma resposta forte a pequenas quantidades de NO2 (10
ppm a 200 ?C). Os nanooctatedros tem maior sensibilidade do que os cristalitos
esf?ricos de mesmo tamanho, e apresentam menor tempo de resposta e menor tempo de
retorno. Estes resultados foram confirmados atrav?s da modelagem da cin?tica de
resposta e de recupera??o do sensor. Testes iniciais de atividade catal?tica na rea??o de
oxida??o do CO entre 100 ? e 350 ? C mostram que o efeito do tamanho ? predominante
em rela??o ao efeito da forma no que diz respeito ? convers?o da rea??o. A morfologia
dos cristalitos nanom?tricos influenciou a taxa da rea??o. Uma maior taxa de rea??o ?
obtida em presen?a de nanooctaedros. A fim de melhorar as propriedades de detec??o e
catal?ticas do material, n?s desenvolvemos uma metodologia de hierarquiza??o de
nanocristalitos que envolve o uso de templates a base de carbono. / This thesis is part of research on new materials for catalysis and gas sensors
more active, sensitive, selective. The aim of this thesis was to develop and characterize
cobalt ferrite in different morphologies, in order to study their influence on the electrical
response and the catalytic activity, and to hierarchize these grains for greater diffusivity
of gas in the material. The powders were produced via hydrothermal and solvothermal,
and were characterized by thermogravimetric analysis, X-ray diffraction, scanning
electron microscopy, transmission electron microscopy (electron diffraction, highresolution
simulations), and energy dispersive spectroscopy. The catalytic and electrical
properties were tested in the presence of CO and NO2 gases, the latter in different
concentrations (1-100 ppm) and at different temperatures (room temperature to 350 ?
C). Nanooctahedra with an average size of 20 nm were obtained by hydrothermal route.
It has been determined that the shape of the grains is mainly linked to the nature of the
precipitating agent and the presence of OH ions in the reaction medium. By
solvothermal method CoFe2O4 spherical powders were prepared with grain size of 8 and
20 nm. CoFe2O4 powders exhibit a strong response to small amounts of NO2 (10 ppm to
200 ? C). The nanooctahedra have greater sensitivity than the spherical grains of the
same size, and have smaller response time and shorter recovery times. These results
were confirmed by modeling the kinetics of response and recovery of the sensor. Initial
tests of catalytic activity in the oxidation of CO between temperatures of 100 ?C and
350 ?C show that the size effect is predominant in relation the effect of the form with
respect to the conversion of the reaction. The morphology of the grains influence the
rate of reaction. A higher reaction rate is obtained in the presence of nanooctahedra. In
order to improve the detection and catalytic properties of the material, we have
developed a methodology for hierarchizing grains which involves the use of carbonbased
templates.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/19535 |
| Date | 06 November 2014 |
| Creators | Moriyama, Andr? Luis Lopes |
| Contributors | 13681389420, http://lattes.cnpq.br/1030834608582624, Leroux, Christine, 00000000000, Sousa, Jo?o Fernandes de, 12270202449, http://lattes.cnpq.br/7942158213535430, Arab, Madjid, 00000000000, http://lattes.cnpq.br/9941296974078492, Novak, Miguel Alexandre, 50456601791, http://lattes.cnpq.br/3940543577818673, Madigou, Veronique, 00000000000, Souza, Carlson Pereira de |
| Publisher | Universidade Federal do Rio Grande do Norte, P?S-GRADUA??O EM ENGENHARIA QU?MICA, 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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