Navegando por Autor "Silva, Anderson Gabriel Marques da"
Agora exibindo 1 - 13 de 13
Resultados por página
Opções de Ordenação
Item Air stable ligandless heterogeneous catalyst systems based on Pd and Au supported in SiO2 and MCM-41 for Suzuki–Miyaura cross-coupling in aqueous médium.(2013) Speziali, Marcelo Gomes; Silva, Anderson Gabriel Marques da; Miranda, Débora Michelini Vaz de; Monteiro, Adriano Lisboa; Robles Azocar, Patrícia AlejandraPalladium and palladium-gold containing siliceous-MCM-41 and sol–gel palladium and palladium-gold silica composites have been prepared. The catalytic performance of incorporated Pd/MCM-41, Au- Pd/MCM-41 and Pd and Au-Pd/SiO2 sol–gel catalysts for the Suzuki–Miyaura cross-coupling reaction was determined and the influence of the matrix and the catalyst composition on the catalytic activity were also studied. The catalysts were characterized by N2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The silica-containing palladium and palladium-gold catalysts prepared using the MCM-41 matrix showed greater catalytic activity than using the conventional sol–gel method; however, gold had a significant influence on this reaction. The catalyst did not undergo metal leaching and could be easily recovered and re-used (reused).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 Desenvolvimento de catalisadores nanoestruturados para obtenção de produtos de interesse comercial via processos de oxidação do tioanisol em fase líquida.(2022) Teixeira, Moisés Paulo; Fajardo, Humberto Vieira; Fajardo, Humberto Vieira; Ramalho, Teodorico de Castro; Silva, Anderson Gabriel Marques da; Carreño, Neftalí Lenin Villarreal; Silva, Adilson Cândido daA catálise está presente em pelo menos uma das etapas da maioria dos processos industriais. A literatura científica está repleta de estudos que envolvem o desenvolvimento de materiais para aplicações catalíticas, buscando obtê-los com custo reduzido, que sejam ativos, seletivos, estáveis frente às reações catalisadas e de preferência ambientalmente amigáveis. Com os avanços da pesquisa, é possível produzir materiais nanoestruturados de diversas morfologias. Estes materiais têm demonstrado maiores atividades catalíticas em comparação com os sólidos estendidos. O objetivo desse projeto é desenvolver catalisadores heterogêneos em escala nanométrica, sintetizados por diferentes rotas, visando a aplicação na reação de oxidação do tioanisol, em fase líquida, para obtenção de produtos de interesse industrial. Foram preparados, como catalisadores, nanofios de CeO2 e nanofios de CeO2 decorados com nanopartículas de ouro (Au-CeO2#nw), além de materiais análogos obtidos a partir do CeO2 comercial. Utilizou- se o método hidrotérmico para a preparação dos materiais. Observou-se que os nanofios de Au- CeO2, apresentaram desempenhos catalíticos significativamente melhores comparativamente aos demais catalisadores. Pôde ser alcançada conversão de até 90% sobre esse catalisador, com 100% de seletividade para metil fenil sulfóxido. Preparou-se, também, catalisadores à base de titanato de estrôncio (STO) e titanato de estrôncio recoberto com óxido de nióbio (STO/Nb2O5) por dois métodos: método Pechini e método hidrotérmico assistido por micro-ondas (MHAM). O catalisador STO/Nb2O5 demonstrou maior atividade catalítica para essas reações quando comparado ao STO puro, alcançando 100% de conversão do reagente e 100% de seletividade para metil fenil sulfona. Por fim, foram preparados catalisadores de sílica sintética (SiO2), sílica dopada com 5% de nióbio (Nb5%SiO2) e sílica dopada com 10% de nióbio (Nb10%SiO2). Os catalisadores com nióbio foram obtidos a partir da impregnação da SiO2 com uma solução de oxalato amoniacal de nióbio. A presença do nióbio na matriz impulsionou a atividade catalítica, atingindo-se 88% de conversão sobre o catalisador (Nb10%SiO2). De um modo geral, os catalisadores preparados durante essa pesquisa demonstraram desempenhos equiparáveis e, em alguns casos, superiores àqueles apresentados por catalisadores relatados na literatura. Cabe ressaltar também que os resultados obtidos nesse estudo, através da utilização de catalisadores heterogêneos associados a um agente oxidante ambientalmente amigável, como o peróxido de hidrogênio, em condições reacionais relativamente brandas, podem se tornar economicamente atrativos, satisfazendo os ideais da química verde.Item Efficient ceria – silica catalysts for BTX oxidation : probing the catalytic performance and oxygen storage.(2016) Silva, Anderson Gabriel Marques da; Fajardo, Humberto Vieira; Balzer, Rosana; Probst, Luiz Fernando Dias; Prado, Nayara Teodoro do; Camargo, Pedro Henrique Cury; Robles Azocar, Patrícia AlejandraThis paper describes a systematic investigation on the synthesis of CeO2 supported on SiO2 by two different methods: (i) the in situ incorporation of CeO2 onto MCM-41 and (ii) wet impregnation. We were interested in investigating how the CeO2 preparation could influence their physicochemical properties and catalytic performances towards the benzene, toluene, and o-xylene (BTX) oxidation reactions. Our results showed that the catalytic performances were strongly dependent on the synthetic approach, in which the CeO2–MCM-41 material prepared by the in situ incorporation showed better BTX oxidation activities than the CeO2-based catalysts prepared by conventional wet impregnation. This result could be assigned to the higher specific surface area, better interaction between CeO2 and the support, improved Ce4+/Ce3+ redox process, and higher concentration of oxygen vacancies as enabled by the in situ approach. The influence of CeO2 content in the ordering of the SiO2 mesoporous structure was also demonstrated.Item Gold, palladium and gold–palladium supported on silica catalysts prepared by sol–gel method : synthesis, characterization and catalytic behavior in the ethanol steam reforming.(2013) Silva, Anderson Gabriel Marques da; Robles Azocar, Patrícia Alejandra; Dias, Anderson; Fajardo, Humberto Vieira; Lovón, Adriana Siviero Pagani; Quintana, Juan José Lovón; Valença, Gustavo PaimNoble-metal-based catalysts supported on silica (Au/SiO2, Pd/SiO2 and Au–Pd/SiO2) were prepared by the sol–gel method and were evaluated in the steam reforming of ethanol for hydrogen production. The catalysts were characterized by N2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The structural characterization of the Au- and Pd-containing catalysts after calcination showed that the solids are predominantly formed by Au0 , Pd0 and PdO species and was observed that the metallic Pd dispersion diminished in the presence of Au0 . The results revealed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. The Pd/SiO2 catalyst showed the best performance among the catalysts tested at the highest reaction temperature (600 C) due to the more effective action of the metallic active phase, which covers a greater area in this sample. At this same reaction temperature, the Au–Pd/SiO2 catalyst showed a significant deactivation, probably due to the lower Pd dispersion presented by this catalyst.Item MnO2-Ir nanowires : combining ultrasmall nanoparticle sizes, O-Vacancies, and low noble-metal loading with improved activities towards the oxygen reduction reaction.(2022) Lima, Scarllet Lalesca Santos de; Pereira, Fellipe dos Santos; Lima, Roberto Batista de; Freitas, Isabel Cristina de; Spadotto, Julio; Connolly, Brian J.; Barreto, Jade; Stavale, Fernando; Vitorino, Hector Aguilar; Fajardo, Humberto Vieira; Tanaka, Auro Atsushi; Garcia, Marco Aurélio Suller; Silva, Anderson Gabriel Marques daAlthough clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2 -Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2 -Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2 -Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion.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 Obtenção de matrizes dopadas com metais de transição : estudo da atividade catalítica em reações de química fina.(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) Silva, Anderson Gabriel Marques da; Robles Azocar, Patrícia AlejandraEste trabalho foi dividido em duas partes independentes. No capítulo 1, foram preparados catalisadores heterogêneos via processo sol-gel e via MCM-41 utilizando sílica como matriz e os metais transição Pd e Au-Pd como dopantes. Os compósitos de Pd e Au-Pd foram caracterizados por difração de raios X (DRX), análise de adsorção-dessorção de N2 através da equação BET e do método BJH, redução à temperatura programada (RTP), espectrometria de emissão atômica com plasma indutivamente acoplado (ICP-AES) e espalhamento de raios X a baixo ângulo (SAXS). O desempenho catalítico dos compósitos foi avaliado em reações de acoplamento Suzuki através de um sistema catalítico no qual uma série de haletos de arila e o ácido fenilborônico foram utilizados como substratos. Os resultados dos testes indicaram a obtenção de biarilas em rendimentos entre 50 e 99%. Nos testes de reciclo, os catalisadores não mostraram perda significativa da atividade (< 5%). A presença do metal ouro em catalisadores de paládio provocou um aumento na atividade catalítica. Além disso, os catalisadores preparados por MCM-41 também se mostraram mais ativos que os catalisadores preparados por sol-gel. No capítulo 2, foi desenvolvido um processo sustentável que abrange as cadeias produtivas da indústria sucroalcooeira e da química fina interconectado com o desenvolvimento sustentável das mesmas através da valorização de resíduos como o bagaço de cana. Este material orgânico foi utilizado como adsorvente na remoção de contaminantes ambientais e como matriz de catalisadores heterogêneos na valorização de matéria-prima nacional, via oxidação seletiva de componentes dos óleos essenciais, gerando produtos de alto valor agregado.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 Processo de isomerização e de hidratação do β-cariofileno catalisado por heteropoliácido.(2022) Silva, Marcelly Maurício Brandão; Rocha, Kelly Alessandra da Silva; Vieira, Camila Grossi; Rocha, Kelly Alessandra da Silva; Vieira, Camila Grossi; Silva, Anderson Gabriel Marques da; Nogueira, André EstevesNeste trabalho foi desenvolvido um processo catalítico homogêneo via reação de isomerização e hidratação para a valorização do composto sesquiterpênico, β-cariofileno, empregando catalisadores heteropoliácidos (HPAs) comerciais da série de Keggin, particularmente, H3PW12O40·xH2O (ácido fosfotúngstico, HPW), H3PMo12O40·xH2O (ácido fosfomolíbdico, HPMo) e H4SiW12O40·xH2O (ácido silicotúngstico, HSiW). O processo de transformação do β-cariofileno, um dos sesquiterpênicos mais abundantes na natureza, foi realizado em meio ácido sob condições brandas de reação na presença de solventes cetônicos, acetona e butanona. Os principais produtos obtidos no processo foram o (-)-cloveno (via reação de isomerização) e os álcoois sesquiterpênicos, β-cariolanol e β-clovanol (via reação de hidratação). A quantidade de água de hidratação presente nos solventes cetônicos (acetona ou butanona), bem como nos catalisadores comerciais empregados foi suficiente para a formação dos compostos β-cariolanol e β-clovanol, sem a necessidade de adição de água extra ao sistema catalítico. Os experimentos em condições otimizadas empregando HPW, HSiW e HPMo em solução de butanona e acetona apresentaram perfis reacionais similares e também, melhor desempenho catalítico em comparação ao catalisador ácido convencional, H2SO4, obtendo rendimento total em torno de 70-80% para os três produtos principais. Os produtos obtidos apresentam aplicação nas indústrias farmacêuticas e de perfumaria e apresentam valor comercial expressivamente superior ao do β-cariofileno. Até o presente momento, não existem relatos de estudos empregando catalisadores a base de heteropoliácido para o desenvolvimento de um processo de transformação do β-cariofileno envolvendo reações de hidratação e isomerização realizadas de modo simultâneo, sendo inédita a aplicação do HPW, HPMo e HSiW no desenvolvimento do processo aqui descrito.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 Synergistic effect between CeO2 nanowires and gold NPs over the activity and selectivity in the oxidation of thioanisole.(2021) Rosado, Taíssa F.; Teixeira, Moisés Paulo; Moraes, Leonardo César de; Silva, Leonardo A. da; Silva, Augusto V. Pontes; Taylor, Jason Guy; Freitas, Isabel Cristina de; Oliveira, Daniela Coelho de; Gardener, Jules; Solorzano, Guilhermo; Alves, Tiago Vinicius; Venancio, Mateus Fernandes; Silva, Maria Isabel Pais da; Brocchi, Eduardo de Albuquerque; Fajardo, Humberto Vieira; Silva, Anderson Gabriel Marques daGold nanoparticles incorporated on ceria nanowires have been employed as efficient nanocatalysts for the se lective oxidation of thioanisole. The control of both physical and chemical parameters as well as metal–support interactions are important factors that determine their performances. Considering their one-dimensional morphology with large surface area, thin diameters, high concentration of oxygen vacancies, and small Au NPs uniformly on the entire CeO2 surface with a high fraction of oxidized gold species, these characteristics make them favorable nanocatalysts for oxidation transformations. The CeO2-Au nanowires displayed improved per formances towards the oxidation of thioanisole when compared to the pure CeO2 nanowires and commercial CeO2-Au catalysts. The CeO2-Au nanowires catalyzed the selective synthesis of methyl phenyl sulfoxide with up to 100 % of selectivity and high conversion. The impact of solvent and temperature during the catalytic reaction was also experimentally and theoretically investigated by DFT calculations, indicating a key role in the observed activities.