VIVIAN VAZQUEZ THYSSEN
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Resumo IPEN-doc 29198 Lanthanum-ceria modified with calcium for oxidative coupling of methane2022 - THYSSEN, VIVIAN V.; VILELA, VANESSA B.; FONSECA, FABIO C.Ethylene (C2H4) is considered a fundamental component of the chemical industry, it is a raw material widely used to produce plastics, solvents, fertilizers, etc. Currently, the main route to obtain C2H4is the steam cracking of naphtha from crude oil, a well-established technology that is hardly challenged. The search for more sustainable alternatives must be ongoing, and among the alternative, we can mention the use of natural gas. The oxidative coupling of methane (OCM), the main component of natural gas, is a compelling direct pathway of methane (CH4) conversion into higher added value hydrocarbons, such as C2(C2H6and C2H4). [1] La2Ce2O7catalyst performs well in OCM due to its high thermal stability, suitable alkaline sites, and selective mobile oxygen sites. Doping La2Ce2O7with Ca increases the alkalinity, which can considerably increase C2selectivity in the OCM. We have explored a scalable method of combustion synthesis, a high-throughput technique that provides favorable porous microstructures for stable catalysts at high temperatures. The obtained La2Ce2- xCaxO7powders (0 ≤ x ≤ 0.5) SEM images evidenced a microstructure composed of porous sponge-like agglomerated particles with an irregular shape, expected from the type of synthesis. The materials showed crystalline structures of disordered fluorite and C-type, indicated by both XRD and Raman analysis. Raman spectroscopy data also evidenced the presence of surface oxygen vacancies on materials, which benefited the OCM reaction. The catalytic tests showed us that the addition of Ca increased the C2selectivity by 10%, at 750oC and a CH4:O2molar ratio of 6:1. [2].Artigo IPEN-doc 28661 Direct conversion of methane to C2 hydrocarbons in solid-state membrane reactors at high temperatures2022 - THYSSEN, VIVIAN V.; VILELA, VANESSA B.; FLORIO, DANIEL Z. de; FERLAUTO, ANDRE S.; FONSECA, FABIO C.Direct conversion of methane to C2 compounds by oxidative and nonoxidative coupling reactions has been intensively studied in the past four decades; however, because these reactions have intrinsic severe thermodynamic constraints, they have not become viable industrially. Recently, with the increasing availability of inexpensive “green electrons” coming from renewable sources, electrochemical technologies are gaining momentum for reactions that have been challenging for more conventional catalysis. Using solid-state membranes to control the reacting species and separate products in a single step is a crucial advantage. Devices using ionic or mixed ionic−electronic conductors can be explored for methane coupling reactions with great potential to increase selectivity. Although these technologies are still in the early scaling stages, they offer a sustainable path for the utilization of methane and benefit from the advances in both solid oxide fuel cells and electrolyzers. This review identifies promising developments for solid-state methane conversion reactors by assessing multifunctional layers with microstructural control; combining solid electrolytes (proton and oxygen ion conductors) with active and selective electrodes/catalysts; applying more efficient reactor designs; understanding the reaction/degradation mechanisms; defining standards for performance evaluation; and carrying techno-economic analysis.Artigo IPEN-doc 28526 Enhancing the catalytic activity of lanthanum-ceria fluorite for methane conversion in SOFC2021 - VILELA, V.B.; THYSSEN, V.V.; RODRIGUES, L.N.; FONSECA, F.C.A2B2O7 compounds with tailored compositions exhibit catalytic properties in a variety of high-temperature reactions, such as oxidative coupling of methane (OCM). La2Ce2O7 performs well in OCM due to selective mobile oxygen species, and suitable alkaline sites. Doping with Ca2+ increases the alkalinity, which can considerably increase selectivity for C2 products in OCM. We have explored the combustion synthesis to obtain homogeneous Ca2+-doped La2Ce2O7 materials to use as a catalytic layer in SOFC reactors for methane direct conversion to C2. The addition of Ca2+ in the A site of La2Ce2O7 resulted in the disordered fluorite-type crystalline structure. The formation of superficial oxygen vacancies related to the active oxygen species, which may benefit the OCM reaction, was detected. Electrochemical characterization showed no significant dependence of the conductivity with Ca2+-doping.Artigo IPEN-doc 28525 Development of anode-supported solid oxide fuel cell by co-tape casting and co-sintering2021 - RODRIGUES, L.N.; MACHADO, MARINA; MORAES, L.P.R.; THYSSEN, V.V.; FONSECA, F.C.Simple and cost-effective technologies to produce solid oxide fuel cells require control of microstructure, thickness, homogeneity, and reproducibility of the functional layers. The manufacturing of a solid oxide fuel cell (SOFC) involves significant ceramic processing challenges to obtain layers with controlled microstructure. Possibly the most common technique for large-scale production of SOFCs is tape casting. In this study, YSZ electrolyte and 60NiO/YSZ anode slurries were studied for the production of half-cells deposited by the sequential tape casting technique. A co-sintering procedure was developed for the half-cells and after cathode deposition the single cells were tested.