Navegando por Autor "Rodrigues, Thenner Silva"
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Item Ce1−xSmxO1.9−δ nanoparticles obtained by microwave assisted hydrothermal processing : an efficient application for catalytic oxidation of α-bisabolol.(2014) Silva, Anderson Gabriel Marques da; Rodrigues, Thenner Silva; Dias, Anderson; Fajardo, Humberto Vieira; Gonçalves, Rosana de Fátima; Godinho Júnior, Mário; Robles Azocar, Patrícia AlejandraHeterogeneous catalysts based on Sm-doped ceria were employed for the first time in the liquid-phase oxidation of α-bisabolol. Nanometer-sized catalysts were obtained by microwave-hydrothermal synthesis and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), Raman spectroscopy and N2-physisorption. The influence of Sm doping, temperature and the solvent used on the catalytic behavior was investigated. Conversions up to 84% and a combined selectivity for the products up to 77% were obtained for Ce0.9Sm0.15O1.85−δ catalysts. The reactions were highly selective for the epoxidation products (only bisabolol oxides A and B were obtained) and shown to be strongly dependent on the temperature and solvent employed. Best results were achieved for higher Sm concentrations, which indicate that changes in the textural properties due to doping produced a significantly more active catalyst.Item Combining active phase and support optimization in MnO2-Au nanoflowers : enabling high activities towards green oxidations.(2018) Silva, Anderson Gabriel Marques da; Rodrigues, Thenner Silva; Candido, Eduardo Guimarães; Freitas, Isabel Cristina de; Silva, Alisson Henrique Marques da; Fajardo, Humberto Vieira; Balzer, Rosana; Gomes, Janaina Fernandes; Assaf, Jose Mansur; Oliveira, Daniela Coelho de; Oger, Nicolas; Paul, Sebastien; Wojcieszak, Robert; Camargo, Pedro Henrique CuryAmong the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.Item Matrizes inorgânicas dopadas com metais de transição : preparo, caracterização e aplicação como catalisadores na dessulfurização oxidativa de combustíveis líquidos.(Programa de Pós-Graduação em Engenharia de Materiais. Rede Temática em Engenharia de Materiais, Pró-Reitoria de Pesquisa e Pós-Graduação, Universidade Federal de Ouro Preto., 2013) Rodrigues, Thenner Silva; Robles Azocar, Patrícia AlejandraA remoção de compostos sulfurados de combustíveis tem atraído muito interesse de pesquisadores nos últimos anos, impulsionados pela crescente rigidez das legislações ambientais, pois a queima destes compostos gera óxidos de enxofre (SOx), causadores de impactos ambientais como a chuva ácida. Diante disso, tecnologias de dessulfurização de combustíveis têm sido desenvolvidas, como por exemplo, a dessulfurização oxidativa (ODS), na qual os compostos sulfurados são oxidados e posteriormente removidos através da extração com solventes polares imiscíveis nos combustíveis. Neste trabalho o foco foi o desenvolvimento de matrizes inorgânicas a base de SiO2, TiO2 e SiO2-TiO2 com altas áreas superficiais e estreita faixa de tamanhao de poros, dopadas com os metais de transição cromo, cério e molibdênio; para utilização como catalisadores heterogêneos em reações de ODS de uma matriz simulada de combustível líquido empregando-se dibenzotiofeno (DBT) como composto sulfurado modelo, iso-octano como matriz simulada de combustível líquido; e peróxido de hidrogênio (H2O2), terc-butil hidroperóxido (tBOOH) e oxigênio molecular (O2) como oxidantes finais do processo. Os materiais foram caracterizadas por análises de difração de raios X (DRX), as quais indicaram que os dopantes inseridos nas matrizes de SiO2, TiO2 e SiO2-TiO2 encontram-se provavelmente homogeneamente dispersos nas superfícies das mesmas; análises de redução à temperatura programada de hidrogênio (H2-RTP), as quais indicaram a presença de fases redutíveis dos constituintes dos catalisadores e fortes interações destas fases com as matrizes dos catalisadores; por medidas de área superficial (Método BET) e distribuição de tamanho de poros (método BJH) via isotermas de adsorção-dessorção de N2, as quais revelaram elevadas áreas superficiais e estreitas faixas de distribuição de tamanho de poros para os catalisadores a base de SiO2 e SiO2-TiO2. Os catalisadores obtidos mostraram-se ativos nos processos de ODS com os diferentes oxidantes e diferenças na atividade catalítica foram observadas entre os catalisadores com diferentes suportes e/ou fases ativas. Em muitos processos executados alcançou-se a oxidação completa do DBT e o único produto observado foi a dibenzossulfona (DBTO2), a qual por apresentar alta polaridade, foi totalmente removida do combutível por extração com acetonitrila.Item A new use for modified sugarcane bagasse containing adsorbed Co2+and Cr3+ : catalytic oxidation of terpenes.(2013) Silva, Anderson Gabriel Marques da; Rodrigues, Thenner Silva; Gurgel, Leandro Vinícius Alves; Assis, Patrícia Aparecida de; Gil, Laurent Frédéric; Robles Azocar, Patrícia AlejandraThis study describes the applicability of two chemically modified sugarcane bagasses containing eitheradsorbed Co2+or Cr3+ions as heterogeneous catalysts for the autooxidation of monoterpenes. The mainobjective was to investigate new uses for these adsorbent materials which had been previously employedfor treatment of aqueous solutions or effluents containing metals such as Co2+and Cr3+. The adsorptionefficiency of Co2+and Cr3+on SCB2 and EB was evaluated by adsorption isotherms and other techniquessuch as XRD, ICP-AES and TGA. Catalytic activity of the four new catalysts, SCB2-Co, SCB2-Cr, EB-Co, andEB-Cr, were assessed in the oxidation reaction of _-citronellol(1), (+)-limonene(2), and (−)- _-pinene(3)in a free solvent system. Results obtained demonstrated that these materials were promising catalysts forthe oxidation of monoterpenes. Reactant conversion ranged from 49 to 78% as determined by GC analysisand a combined selectivity up to 59% for the oxidation products was achieved.Item Otimização das condições reacionais do processo catalítico de oxidação seletiva da anilina a nitrosobenzeno empregando bastões de polioxoniobato contendo cobre.(2022) Luz, Sulusmon César; Fajardo, Humberto Vieira; Fajardo, Humberto Vieira; Rodrigues, Thenner Silva; Lobo, Fabiana AparecidaO presente estudo fornece uma abordagem acerca da aplicação de uma classe de materiais, denominados polioxometalatos, em especial os isopoliânions, estruturados na forma do tipo Lindqvist, possuindo em sua composição química o elemento Nióbio (metal de transição em seu estado de oxidação 5+). Os catalisadores foram sintetizados pela rota de coprecipitação e posteriormente tratados hidrotermicamente, assistidos por irradiação de micro-ondas, em diferentes condições de temperatura e tempo. Os materiais obtidos foram avaliados como catalisadores heterogêneos frente a reação de oxidação da anilina em fase líquida, buscando- se a obtenção seletiva de nitrosobenzeno. A oxidação da anilina em seus respectivos produtos derivados, tais como fenilhidroxilamina, nitrosobenzeno, nitrobenzeno, azobenzeno e azoxibenzeno, gera insumos de excepcional valor agregado e diferentes aplicações no contexto das indústrias químicas, petroquímicas, farmacêuticas, dentre outras. Apesar de um amplo acervo a respeito das aplicabilidades de polioxometalatos encontrados na literatura científica, poucos são os estudos centrados na aplicação destes em reações de substratos orgânicos e seus derivados, particularmente em reações envolvendo as arilaminas. Perante essa premissa, nesse trabalho são apresentados os resultados dos ensaios catalíticos realizados com o objetivo de avaliar preliminarmente o método de síntese dos catalisadores empregado; eficiência dos catalisadores frente a reação de oxidação da anilina, empregando-se como agente oxidante o peróxido de hidrogênio; correlação entre a morfologia do material e a capacidade de conversão do substrato e a seletividade aos produtos derivados. Paralelamente, foi empregado um estudo multivariado com 5 variáveis independentes (tipo do catalisador, volume do agente oxidante, tempo da reação, temperatura de reação e solvente), condições reacionais utilizadas na reação proposta, com o intuito de otimizar o processo através do conhecimento das variáveis que influenciaram diretamente na conversão do substrato e seletividade aos produtos. Empregou-se um planejamento fracionário 25-1 no processo de experimentação de triagem, para a seleção do catalisador, com relação a conversão da anilina como variável dependente e após a seleção das variáveis significativas ao sistema químico em estudo, foi utilizado um planejamento experimental do tipo Doehlert que objetivou a obtenção dos coeficientes significativos e proposição do modelo (linear ou quadrático) que se ajustava ao sistema. De posse dessas informações, foi possível determinar a região ótima de trabalho, através da Metodologia de Superfície de Resposta, obtendo-se deste modo os valores das respectivas variáveis que encaminhavam para a maximização da conversão. O processo de síntese utilizado mostrou-se extremamente eficiente na obtenção de bastões de polioxoniobatos em tempos (10, 20 e 30 minutos) e temperatura (80 a 150oC) relativamente baixos. Em geral, os catalisadores desenvolvidos possuíram potencial para aplicações catalíticas, obtendo-se uma conversão máxima de 97,3% da anilina com 88,9% seletividade para nitrosobenzeno. Para a análise da quantificação das amostras dos ensaios catalíticos deste estudo foi utilizada a técnica de cromatografia gasosa, onde foram feitas as devidas curvas de calibração com as respectivas soluções padrão necessárias para identificação e quantificação dos produtos. Para a caracterização e estudo das propriedades físico-químicas dos materiais catalíticos obtidos foram empregadas as seguintes técnicas: Difração de Raios-X, Espectroscopia de Infravermelho por transformada de Fourier, Microscopia Eletrônica de Transmissão de Alta Resolução, Microscopia Eletrônica de Varredura, Espectroscopia de Refletância Difusa, Espectrometria de Absorção Atômica, Dessorção a Temperatura Programada de Amônia e Oxidação a Temperatura Programada empregando oxigênio.Item Pd-based nanoflowers catalysts : controlling size, composition, and structures for the 4-nitrophenol reduction and BTX oxidation reactions.(2016) Silva, Anderson Gabriel Marques da; Rodrigues, Thenner Silva; Taguchi, Laís Sanako Kato; Fajardo, Humberto Vieira; Balzer, Rosana; Probst, Luiz Fernando Dias; Camargo, Pedro Henrique CuryWe describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au58@Pd42[Au27@ Pd73[Ag20Pd80 and Ag8Pd92[Au12@Pd88[Ag38Pd62, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.Item Preparation, structural characterization and catalytic properties of Co/CeO2 catalysts for the steam reforming of ethanol and hydrogen production.(2012) Lovón, Adriana Siviero Pagani; Quintana, Juan José Lovón; Almerindo, Gizelle Inácio; Valença, Gustavo Paim; Bernardi, Maria Inês Basso; Araújo, Vinícius Dantas de; Rodrigues, Thenner Silva; Robles Azocar, Patrícia Alejandra; Fajardo, Humberto VieiraIn this paper, Co/CeO2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N2 physisorption (BET method), X-ray diffraction (XRD), UVevisible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physicalechemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 _C.Item Sub-15 nm CeO2 nanowires as an efficient nonnoble metal catalyst in the room-temperature oxidation of aniline.(2018) Silva, Anderson Gabriel Marques da; Batalha, Daniel Carreira; Rodrigues, Thenner Silva; Candido, Eduardo Guimarães; Luz, Sulusmon Cesar; Freitas, Isabel Cristina de; Fonseca, Fabio Coral; Oliveira, Daniela Coelho de; Taylor, Jason Guy; Torresi, Susana Ines Cordoba de; Camargo, Pedro Henrique Cury; Fajardo, Humberto VieiraWe described herein the facile synthesis of sub-15 nm CeO2 nanowires based on a hydrothermal method without the use of any capping/stabilizing agent, in which an oriented attachment mechanism took place during the CeO2 nanowire formation. The synthesis of sub-15 nm CeO2 nanowires could be achieved on relatively large scales (∼2.6 grams of nanowires per batch), in high yields (>94%), and at low cost. To date, there are only a limited number of successful attempts towards the synthesis of CeO2 nanowires with such small diameters, and the reported protocols are typically limited to low amounts. The nanowires displayed uniform shapes and sizes, high surface areas, an increased number of oxygen defects sites, and a high proportion of Ce3+/Ce4+ surface species. These features make them promising candidates for oxidation reactions. To this end, we employed the selective oxidation of aniline as a model transformation. The sub-15 nm CeO2 nanowires catalyzed the selective synthesis of nitrosobenzene (up to 98% selectivity) from aniline at room temperature using H2O2 as the oxidant. The effect of solvent and temperature during the catalytic reaction was investigated. We found that such parameters played an important role in the control of the selectivity. The improved catalytic activities observed for the sub-15 nm nanowires could be explained by: i) the uniform morphology with a typical dimension of 11 ± 2 nm in width, which provides higher specific surface areas relative to those of conventional catalysts; ii) the significant concentration of oxygen vacancies and high proportion of Ce3+/Ce4+ species at the surface that represent highly active sites towards oxidation reactions; iii) the crystal growth along the (110) highly catalytically active crystallographic directions, and iv) the mesoporous surface which is easily accessible by liquid substrates. The results reported herein demonstrated high activities under ambient conditions, provided novel insights into selectivities, and may inspire novel metal oxide-based catalysts with desired performancesItem Synthesis of NiMoO4 ceramics by proteic sol-gel method and investigation of their catalytic properties in hydrogen production.(2021) Silva, Maíra Vieira da; Fajardo, Humberto Vieira; Rodrigues, Thenner Silva; Silva, Felipe A. e; Bergamaschi, Vanderlei Sérgio; Dias, Anderson; Siqueira, Kisla Prislen FélixA proteic sol-gel route was used in the production of NiMoO4 catalysts, which used edible gelatin as a precursor. The triple helix structure of a protein in contact with identical structures acquires an unfolded form, which favors the interaction of the reactive groups of the gelatin (NH3 + and COO− ) with the metallic ions (MoO4 2− and Ni2+). The synthesized catalysts were thoroughly characterized using techniques such as X-ray diffraction, thermog ravimetric and differential thermal analysis, Raman scattering, scanning and transmission electron microscopies, UV–Vis spectroscopy, and colorimetry. The results showed that it is possible to prepare the phase-pure α-NiMoO4 polymorph only at temperatures above 700 ◦C, while a mixture of the polymorphs α and β were obtained at lower temperatures. The synthesized materials calcined at 300, 500, and 700 ◦C have their catalytic potentials tested in the ethanol steam reforming reaction aiming the production of hydrogen and presented a good performance. The results indicated that among tested materials, the sample calcined at 700 ◦C exhibited the highest stability, activity, and best selectivity relative to the product of interest.Item Synthesis, characterization and catalytic potential of MgNiO2 nanoparticles obtained froma novel [MgNi(opba)]n . 9nH2O chain.(2016) Rodrigues, Thenner Silva; Fajardo, Humberto Vieira; Dias, Anderson; Mezzalira, Daniela Paula Dal Zot; Probst, Luiz Fernando Dias; Stumpf, Humberto Osório; Barros, Wdeson Pereira; Profiles, Gilmar Pereira SouzaWe describe herein the synthesis of MgNiO2 nanoparticles employing a new one-dimensional system [MgNi(opba)]n . 9nH2O, with opba standing for ortho-phenylenebis(oxamato), as precursor. The MgNiO2 nanoparticles could be obtained after heat-treatment at 800 °C for 5 h under air atmosphere, which was responsible for the elimination of water and organic precursor material leading the formation of na- noparticles with average size of 40 7 9 nm. To this end, we first described the synthesis of [MgNi (opba)]n . 9nH2O chain, which was obtained using a pre-synthetized Na2[Ni(opba)] . 5H2O and Mg2 þ (molar ratio of 1:1) in aqueous media and then this chain was calcined to produce the desired MgNiO2 nanoparticles. The obtained MgNiO2 nanoparticles showed good catalytic performance towards ethanol decomposition achieving 100% of substrate conversion and producing acetaldehyde (56.8%) and hydro- gen (24.8%) as the main gaseous products. Also, carbon based structures of great interest for technolo- gical applications, carbon nanotubes and onions were formed as valuable byproducts. Thus, we believe that our reported results may inspire the synthesis of catalysts with improved performances for appli- cations in other gas-phase transformations.