The catalytic activity of the Pr2Zr2-xFexO7±d system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO2, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr2Zr2-xFexO7±d (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO2 sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.Postprint (published version

Structural and electrical properties of Zr-doped K0.48 Na 0.52 NbO 3 ceramics: “Hard” lead-free piezoelectric

The structural and electrical properties of K0.48Na0.52Nb1−xZrxO3−δ (x = 0–0.04) ceramics prepared by the conventional solid-state reaction method were studied. Pellets with composition x ≤ 0.03 sintered at 1125 °C for 2 h showed single-phase of potassium sodium niobate (KNN) perovskite structure. Based on X-ray diffraction and Raman results, a mixture of orthorhombic and monoclinic phases was observed in intermediate compositions. The addition of Zr improved the sinterability and the “hard” piezoelectric properties of KNN, increasing the Ec and Qm values. The composition with x = 0.03 presented the highest permittivity at room temperature, ɛr′ = 363 and the lowest dielectric losses, tan δ = 0.027. Moreover, it was the sample with the highest Qm and d33 values, with Qm = 1781 and d33 = 82 pC/N. It was therefore the best compositions to obtain a “hard” piezoelectric material based on Zr-doped KNN, which makes it promising candidate for use as “hard” lead-free piezoelectric material for high power applications

Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study

PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.

PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Materials based on RE2Zr2O7 compositions: a comprehensive study on advanced properties and multifunctional applications

Compendi d'articles. Doctorat internacional.In the face of imminent challenges posed by climate change, urgent strides in sustainable development, particularly in energy-efficient alternatives, are crucial. Technological advancements, especially in advanced materials, are key factors contributing to the achievement of the Sustainable Development Goals (SDGs) outlined in the United Nations' 2030 Agenda. This thesis focuses on enhancing advanced materials, specifically RE2Zr2O7 compositions, through innovative synthesis methods for energy-efficient and environmentally sustainable applications. The incorporation of rare-earth elements (REEs) in A2B2O7-type structures shows promise in electroceramic materials, catalytic converters, and photocatalysts. Divided into four parts, the thesis introduces A2B2O7 structures and outlines the doctoral thesis objectives. Results encompass electrical properties studies and catalytic applications of various compositions. The thesis concludes by emphasizing the materials' potential contributions to technological advancements addressing both energy and environmental issues.Programa de Doctorat en Cièncie

Análise de roteiros experimentais de Quí­mica presentes nos livros didáticos aprovados pelo Programa Nacional do Livro Didático - triênio 2015-2017

A experimentação no Ensino de Quí­mica tem como objetivo ilustrar teorias para facilitar o aprendizado, além de criar um ambiente favorável para a discussão de temas pertinentes à sociedade. Logo, deve ser constantemente utilizada pelo professor. Porém, nos últimos anos, vem sendo criticada por estudiosos da área por não alcançar seus principais objetivos. Conforme os critérios presentes no guia do Programa Nacional do Livro Didático (PNLD) de Quí­mica, também em concordância com os Parâmetros Curriculares Nacionais para o Ensino Médio e as Diretrizes Curriculares da Educação Básica do Estado do Paraná para a disciplina de Quí­mica, a experimentação deve adotar uma metodologia construtiva e investigativa, como o enfoque CTS ou CTSA, abandonando então a abordagem tradicional, que prioriza a reprodução de um roteiro de forma mecânica, sem a constante participação dos estudantes. Este trabalho é voltado para a busca de experimentos no livro didático, instrumento presente desde antes da metade do século passado nas escolas brasileiras. Foram analisados todos os 128 experimentos das quatro coleções de Quí­mica selecionadas pelo PNLD de 2015, averiguando se as propostas de atividades experimentais estão de acordo com o que é exigido nos documentos oficiais, com temas contextualizados, que proporcionem não só a construção do conhecimento, mas também a alfabetização cientí­fica. Após a análise verificou-se que cada coleção faz uso da experimentação com frequências e metodologias diferentes, além disso, alguns temas, principalmente no terceiro volume de cada coleção poderiam ser melhor explorados. Algumas obras não trazem avisos suficientes de segurança ou descarte adequado de resí­duos, fatores importantes para a correta execução de uma aula experimental. Por fim, é perceptí­vel a necessidade de pequenas adaptações metodológicas e informativas nos livros selecionados pelo PNLD, para que a experimentação atinja seus objetivos e contribua para o desenvolvimento cientí­fico-social do aluno, associado também ao compromisso ambiental

Evaluation of Pr2Zr2-xCexO7±δ pyrochlores as a potential Cu support catalysts for CO oxidation in simulated GDI conditions

This study evaluates the catalytic activity, both as bulk catalysts and as supports for copper catalysts for CO oxidation in a simulated Gasoline Direct Injection Engine (GDI) of two pyrochlores: Pr2Zr2O7 (PZ) and Pr2Zr1.9Ce0.1O7±δ (PZC). These pyrochlores were synthesized by the solvothermal method. XRD, FE-SEM, HR-TEM, XPS, H2-TPR, and O2-TPD characterization techniques were employed to determine the structural, microstructural, and redox properties of the samples. All materials exhibited high catalytic activity for CO oxidation, with Cu-PZC showing the best performance, which is comparable to that of a 1% Pt/Al2O3 commercial catalyst used as a reference. Thus, the synthesized solids could be a promising and cost-effective alternative to noble metal-based catalysts used to control GDI exhaust gas composition.H.B-M, E.C. and E.L.S.V. thank the Spanish Government (Ministerio de Ciencia e Innovación, Project PID2020-116149GB-I00) for the financial support. E.L.S.V thanks the Generalitat Valenciana for the predoctoral contract (GRISOLIA/2019/054) and for the financial support for the international stay (CIBEFP/2021/22). A.D-V and MJ.I-G thank the Spanish Government (Ministerio de Ciencia e Innovación, Project PID2019-105542RB-I00), the European Union (FEDER Funds) and the Regional Government (Generalitat Valenciana, Project CIPROM/2021-070) for the financial support. A.D-V thanks the University of Alicante the financial support for the predoctoral contract

Understanding the rapid reoxidation process and the electrical properties of Spark Plasma sintered pyrochlores

Pyrochlore structures with composition Pr2−xSmxZr2O7 (x = 0, 1, and 2) were synthetized and studied. Spark Plasma Sintering (SPS) was employed to produce ceramics with over 95% of relative density. The reoxidation behavior and the influence of the sintering process on the electrical properties were studied by Electrochemical Impedance Spectroscopy. The overall conductivity of the materials is higher for the samples with Pr, while the introduction of Sm induced an additional electrical contribution. The reoxidation of the samples presented fast kinetics and increased conductivity, particularly in the PrSmZr2O7 (PSZO) sample. PSZO also exhibits a total conductivity comparable to that of the reference materials used as ionically conductive solid electrolytes. The prepared ceramics, especially the PSZO sample, demonstrate excellent relative density, good conductivity, and fast oxidation, holding promise for applications such as Solid Oxide Fuel Cells, gas sensors, and clean energy technologies that require thermal and physical stability, as well as rapid oxidation-reduction processes