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Previous issue date: 2011-07-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The main goal of this work was to produce nanosized ceramic materials of the
family of the tungstates (tungstates of cerium and strontium), and test them for their
catalytic activity in processes involving the transformation of methane (CH4). The
methodology used for the synthesis of the ceramic powders involved the complexation
combining EDTA-citrate. The materials characterization was performed using simple
and differential thermogravimetry, x-ray diffraction, transmission electron microscopy,
and energy dispersive spectroscopy (EDS). The microstructure analysis was performed
using the refinement by the Rietveld method, and the crystallite size and distribution of
the materials was elucidate by the Scherrer and Williamson-Hall methods. The
conditions of the synthesis process for the three envisaged materials (SrWO4, SrWO4
using tungsten oxide concentrate as raw material, and Ce2(WO4)3) were adjusted to
obtain a single phase crystalline material. The catalytic tests were carried out in the
presence of methane and synthetic air, which is composed of 21% O2 and 79% N2. The
analysis of the conversion of the reaction was done with the aid of an fourier transform
infrared device (FTIR). The analysis showed that, structurally, the SrWO4 produced
using raw materials of high and poor purity (99% and 92%, respectively) are similar.
The ideal parameters of calcination, in the tested range, are temperature of 1000 ?C and
time of calcination 5 hours. For the Ce2(WO4)3, the ideal calcination time and are
temperature 15 hours and 1000?C, respectively. The Williamson-Hall method provided
two different distributions for the crystallite size of each material, whose values ranged
between the nanometer and micrometer scales. According to method of Scherrer, all
materials produced were composed of nanometric crystallites. The analyses of
transmission electron microscopy confirmed the results obtained from the Williamson-
Hall method for the crystallite size. The EDS showed an atomic composition for the
metals in the SrWO4 that was different of the theoretical composition. With respect to
the catalytic tests, all materials were found to be catalytically active, but the reaction
process should be further studied and optimized. / O objetivo principal deste trabalho foi produzir materiais cer?micos
nanom?tricos da fam?lia dos tungstatos (tungstatos de c?rio e de estr?ncio), e test?-los
quanto ?s suas atividades catal?ticas em processos envolvendo a transforma??o do g?s
metano (CH4). A metodologia empregada para a s?ntese dos p?s cer?micos envolveu o
m?todo de complexa??o combinando EDTA-Citrato. A caracteriza??o dos materiais foi
feita atrav?s das t?cnicas de termogravimetria simples e diferencial, difra??o de raios-x,
microscopia eletr?nica de transmiss?o, e espectroscopia de energia dispersiva (EDS). A
an?lise da microestrutura foi realizada atrav?s do refinamento utilizando o m?todo de
Rietveld, e para a estima??o do tamanho de gr?o e de sua distribui??o foram utilizados
os m?todos de Scherrer e Williamson-Hall. As condi??es de obten??o dos tr?s materiais
desenvolvidos (SrWO4, SrWO4 utilizando concentrado de ?xido de tungst?nio como
mat?ria-prima, e Ce2(WO4)3) foram ajustadas para a obten??o de um material cristalino
monof?sico. Os testes catal?ticos explorat?rios foram realizados na presen?a dos gases
metano e ar sint?tico, composto por 21% de O2 e 79% N2. A an?lise da convers?o foi
feita com o aux?lio de um equipamento de infravermelho ? transformada de Fourier. As
an?lises mostraram que, estruturalmente, os materiais SrWO4 produzidos com mat?riaprima
de elevada pureza (99% de pureza) e oriunda do concentrado de ?xido de
tungst?nio (92% de pureza) s?o semelhantes. Seus par?metros ideais de produ??o,
dentro do que foi testado, s?o temperatura de calcina??o de 1000?C e tempo de
perman?ncia de 5 horas na isoterma. Para o Ce2(WO4)3, as condi??es ideais dentro do
que foi testado s?o temperatura de calcina??o de 1000?C e tempo de perman?ncia na
isoterma de 15 horas. O m?todo de Williamson-Hall forneceu duas distribui??es
diferentes para o tamanho de cristalito de cada material, cujos valores oscilaram entre as
escalas nanom?tricas e microm?tricas. Com o m?todo de Scherrer, todos os materiais
produzidos possu?ram tamanho de cristalito nanom?trico. As an?lises de microscopia
eletr?nica de transmiss?o confirmaram o resultado obtido com o m?todo de Williamson-
Hall para o tamanho de cristalito. A EDS indicou a presen?a de diverg?ncias entre a
composi??o at?mica met?lica te?rica e experimental do SrWO4. Com rela??o aos testes
catal?ticos explorat?rios, os materiais se mostraram ativos por?m o processo reacional
ainda precisa ser melhor estudado e otimizado.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/15812 |
| Date | 21 July 2011 |
| Creators | Moriyama, Andr? Luiz Lopes |
| Contributors | CPF:13681389420, http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4781094H3, Santos, Andarair Gomes dos, CPF:02813010421, http://lattes.cnpq.br/3470634368296605, Costa, Francin? Alves da, CPF:45327220478, http://lattes.cnpq.br/8698567925323942, Souza, Carlson Pereira de |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Engenharia Qu?mica, UFRN, BR, Pesquisa e Desenvolvimento de Tecnologias Regionais |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| 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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