Banca de QUALIFICAÇÃO: SERGIO DAMASCENO
Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.DISCENTE : SERGIO DAMASCENO
DATA : 20/04/2022
HORA: 14:00
LOCAL: Remoto
TÍTULO:
Ceria-based Catalysts Applied to Methane Conversion
PÁGINAS: 50
RESUMO:
Rare-earth-doped ceria is a material widely investigated for applications in which oxygen ion transport is relevant, including fuel cells and catalysis. In light of this, the project consists of the development of ceria-based catalysts for efficient thermochemical methane conversion at high temperatures. In a first part of the project ceria nanocubes were obtained by a hydrothermal synthesis route and the synthesis parameters were optimized to tune nanocubes size. The nanocubes were chosen due to the high thermal stability during the sintering and three different sizes distribution were obtained: < 50 nm, 50 to 100 nm, and 300 nm. The general aim is to evaluate the role of oxygen storage capacity, the thermal stability through dilatometry studies and chemical looping experiments at high temperatures, coupled with studies on surface area evolution, morphology changes and the nanocubes behavior by doping the material with lanthanum. The doping with lanthanum, La3+, which is a cation with a larger ionic radius promotes oxygen vacancies formation by charge balance and significant disorder in the fluorite structure that can be beneficial for applications such as catalysis. Therefore, in a second part, ceria-based catalysts were investigated in terms of the correlation between transport properties, defect chemistry and crystalline structure of lanthanum-doped ceria dense pellets (Ce1-xLaxO2-x/2) with 0 ≤ x ≤ 70 at.%. The transport properties were studied by electrochemical impedance spectroscopy and the results show that ionic conductivity increases with increasing La3+ concentration for x ≤ 5 at.%, remains constant up to 15 at.%, and decreases for x> 20 at.%. For low lanthanum-doping (<5 at.%), conductivity increases as a result of the increase in the number of oxygen vacancies, whereas, above 20 at.%, electrostatic and steric interactions between dopant and vacancies (defects) lead to clusters formation that are associated to lower mobility. In this regard, the activation energies decreases for lower doping and for x> 20 at.% it increases, which indicates an increased electrical resistance for defect migration. Moreover, X-ray diffraction and Raman spectroscopy provided insights on the structural changes on fluorite crystal structure. Scanning electron microscopy studies were used to investigate grain boundary and bulk evolution with the doping.
MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1545738 - MARCIA TSUYAMA ESCOTE
Membro Titular - Examinador(a) Interno ao Programa - 1305186 - SERGIO BROCHSZTAIN
Membro Titular - Examinador(a) Interno ao Programa - 1671394 - HUMBERTO NAOYUKI YOSHIMURA
Membro Titular - Examinador(a) Externo à Instituição - DANIEL ARAUJO DE MACEDO - UFPB
Membro Suplente - Examinador(a) Interno ao Programa - 1545089 - DANIEL ZANETTI DE FLORIO
Membro Suplente - Examinador(a) Interno ao Programa - 1734912 - ROOSEVELT DROPPA JUNIOR
Membro Suplente - Examinador(a) Externo à Instituição - FÁBIO CORAL FONSECA - IPEN
Membro Suplente - Examinador(a) Externo à Instituição - VICTOR BURATTO TINTI