Navegando por Autor "Fajardo, Humberto Vieira"

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1D coordination polymer based on copper(II)-containing tetrameric 1,2,3- triazole ligand from click chemistry : magnetic and catalytic properties.
(2019) Teixeira, Leonardo César de Moraes; Souza, Gilmar Pereira de; Fajardo, Humberto Vieira; Luz, Sulusmon Cesar; Álvarez, Eleuterio; Lloret, Francesc; Viana, Renato Márcio Ribeiro; Rojo Marcos, Francisco Javier; Stumpf, Humberto Osório; Figueiredo, Rute Cunha; Correa, Rodrigo de Souza
A novel tetrameric tetra[O-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)]-pentaerythritol (TBTP) has been synthesized using click chemistry strategy. TBTP was characterized and used as ligand to form new Cu(II) complexes, forming 1-D coordination polymers. Two square planar complexes were characterized by single-crystal X-ray diffraction, presenting formula [Cu(TBTP)][Cu(NO3)4] (1) and [Cu(TBTP)](NO3)2 (2). In both structures, a cationic 1-D coordination polymer (CP) has been formed. The CP contain a 1:1 Cu(II)/TBTP ratio with four neutral triazole groups coordinating the Cu(II) center, forming a CuN bonds ranging 1.988(2)–2.001(2) Å. The study of the magnetic properties of compounds 1 and 2 pointed to an antiferromagnetic behavior for both compounds, defined by inter- and intra-chain dipolar interactions among their metallic centers. In addition, the complex 1 was found to be an efficient catalyst for selective oxidation of aniline to azobenzene under mild reaction conditions.
Amorphization effects on the basic sites of nanometric magnesium oxide.
(2008) Carreño, Neftalí Lenin Villarreal; Keyson, David; Escote, Marcia Tsuyama; Leite, Edson Roberto; Longo, Elson; Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias; Valentini, Antoninho; Joya, Miryam Rincón; Pizani, Paulo Sergio
The paper reports the catalytic action of the basic sites of nanocrystalline particles of rare earth-doped magnesium oxide in the aldolization reaction between acetone and methanol leading to the C–C bond formation of an a,b-unsaturated compound (methyl vinyl ketone), also forming methyl ethyl ketone and isopropyl alcohol. Undoped and doped MgO samples were prepared by high-energy mechanical milling of commercial Mg, Y and Ce oxide powders. Catalytic activity and surface basicity of these compounds were strongly influenced by doping and the time of mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. Influence of mechanical processing of these compounds was investigated by means of N2 adsorption (BET), X-ray diffraction (XRD), TEM, CO2 chemisorption and room temperature photoluminescence emission. Strong changes of polar groups such as hydroxyl groups on the surface of the solid were directly related to the photoluminescence emission observed.
Application of Al2O3/AlNbO4 in the oxidation of aniline to azoxybenzene.
(2019) Batalha, Daniel Carreira; Luz, Sulusmon Cesar; Taylor, Jason Guy; Fajardo, Humberto Vieira; Noremberg, Bruno S.; Cherubin, Igor José da Silva; Silva, Ricardo Marques e; Gonçalves, Margarete Regina Freitas; Bergmann, Carlos Pérez; Valentini, Antoninho; Carreño, Neftalí Lenin Villarreal
Al2O3/AlNbO4 powder was fabricated by a facile high-energy milling process. The precursor materials, Al2O3 and Nb2O5, are readily available and have very attractive properties. Moreover, the catalytic activity of the sample in the liquid phase oxidation of aniline (OA) in the presence of hydrogen peroxide as oxidant was evaluated. The catalyst was found to be highly efficient and selective in the oxidation of aniline to azoxybenzene under mild conditions. When mixed with 28% AlNbO4 the alumina-based catalyst achieved high conversion and selectivity and very similar to the pure Nb2O5.
Carbon-coated SnO2 nanobelts and nanoparticles by single catalytic step.
(2009) Carreño, Neftalí Lenin Villarreal; Nunes, Michael Ramos; Garcia, Irene Teresinha Santos; Orlandi, Marcelo Ornaghi; Fajardo, Humberto Vieira; Longo, Elson
Several types of carbon nanostructures (amorphous and graphitic), for the coating of SnO2 nanobelts and nanoparticles were obtained by a single catalytic process, during methane, natural gas, and methanol decomposition using the reactivity of surface-modified SnO2 nanostructure as a nanotemplate. The nanostructured catalyst templates were based on transition metal nanoparticles supported on SnO2 nanobelts previously prepared by a carbothermal reduction process. Carbon-coated SnO2 nanopowders were also successfully synthesized for the fabrication of carbon spheres. The carbon coating process and yield, along with the nature of the nanostructured carbon, are strongly influenced by the chemically modified surface of the SnO2 nanostructure template and the chemical reaction gas composition. The preliminary catalytic activity and gas-sensing properties of these novel materials based on metal nanoparticles and carbon-coated SnO2 were determined.
Catalisadores baseados em óxidos e oxidróxidos de Fe modificados com Nb : obtenção de azoxibenzeno via oxidação de anilina em fase líquida.
(2019) Lima, André Luiz Dias; Silva, Adilson Cândido da; Fajardo, Humberto Vieira; Oliveira, Luiz Carlos Alves de; Nogueira, André Esteves; Silva, Adilson Cândido da
Nesse trabalho a oxidação parcial de anilina em fase líquida foi estudada utilizando catalisadores baseados em óxidos ou oxihidróxidos de ferro modificados com diferentes teores de nióbio. Os materiais sintetizados foram caracterizados por diversas técnicas de caracterização como, difração de raios-x (DRX), isotermas de adsorção/dessorção de N2 (BET), redução a temperatura programada (TPR), microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura (MEV) e espectroscopia de fotoelétrons excitados por raios-x (XPS). A atividade catalítica dos materiais foi avaliada em reações de conversão de anilina. Os dados de DRX confirmam que as fases -FeOOH e -Fe2O3 desejadas foram obtidas e através do refinamento de Rietveld sugeriu-se uma substituição isomórfica de Fe3+ por Nb5+ na estrutura do óxido ou oxihidróxido. Os dados catalíticos mostraram que a presença do Nb é essencial para se obter um catalisador mais ativo para obtenção do azoxibenzeno de maneira seletiva. As hematitas em particular têm essa atividade realçada pelo tratamento prévio com peróxido de hidrogênio (H2O2 ‒ 35%), que fez com que o tempo de reação para conversão total do substrato fosse reduzido de 24 horas para 3 horas. Para os catalisadores baseados em - FeOOH puro, sem a presença de Nb, a conversão alcançada foi de 60,6% do substrato com seletividade a azoxibenzeno de 72%, enquanto que o material contendo 10% em massa de Nb converteu o substrato de maneira completa com seletividade à azoxibenzeno de 70% após 24h de reação. Para a hematita, -Fe2O3, contendo 0% em massa de Nb a conversão do substrato foi de 76,5% e seletividade a azoxibenzeno foi de 33,7%, ao mesmo tempo que para o material contendo 10% de Nb e tratado previamente com H2O2 ‒ 35%, a conversão foi de 100,0% e seletividade a azoxibenzeno foi de 80,5%. Esses resultados mostram que esses catalisadores se mostram ativos para esse tipo de reação e externam a importância da incorporação do Nb5+ para conversão da anilina ao produto de interesse azoxibenzeno. Além disso, os dados sugerem que há um efeito sinérgico entre o peróxido de hidrogênio e o Nb nos catalisadores que auxiliam na interpretação dos resultados.
Catalytic oxidation of volatile organic compounds (n-hexane, benzene, toluene, o-xylene) promoted by cobalt catalysts supported on γ-Al2O3-CeO2.
(2014) Balzer, Rosana; Probst, Luiz Fernando Dias; Drago, V.; Schreiner, W. H.; Fajardo, Humberto Vieira
Cobalt catalysts supported on γ-alumina, ceria and γ-alumina-ceria, with 10 or 20%wt of cobalt load, prepared by the wet impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission transmission electron microscopy (FETEM), N2 adsorptiondesorption isotherms (BET/BJH methods), energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS), O2-chemisorption and temperature programmed reduction (TPR) were used to promote the oxidation of volatile organic compounds (n-hexane, benzene, toluene and o-xylene). For a range of low temperatures (50-350 °C), the activity of the catalysts with a higher cobalt load (20% wt) was greater than that of the catalysts with a lower cobalt load (10% wt). The Co/γ-Al2O3-CeO2 catalytic systems presented the best performances. The results obtained in the characterization suggest that the higher catalytic activity of the Co20/γ-Al2O3-CeO2 catalyst may be attributed to the higher metal content and amount of oxygen vacancies, as well as the effects of the interaction between the cobalt and the alumina and cerium oxides.
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 Alejandra
Heterogeneous 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.
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 Cury
Among 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.
Correlation of catalytic oxidation and ionic conductivity properties of nanostructured gadolinium-doped ceria.
(2021) Godinho Júnior, Mário; Rodrigues, Murillo H. M.; Gonçalves, Rosana de Fátima; Roca, Román Alvarez; Longo, Elson; Mota, Fabiana Villela; Fajardo, Humberto Vieira; Balzer, Rosana
This paper reports the relationship between ionic conductivity and catalytic activity of ionic conductors based on gadolinium-doped ceria (GDC) at different temperatures. The samples have been characterized by transmission electron microscopy techniques, and the results indicated a highly homogeneous particle size, which confirmed their nanometric size. Afterward, the structure determined using X-ray diffraction analysis has been used to analyze the effect of dopant insertion. Lastly, ionic conductivity data were obtained using the impedance technique and were compared with the conversion rates of volatile organic compounds using GDC heterogeneous catalysts. The samples containing 15% gadolinium presented higher catalytic activity for the oxidation of n hexane (82,5%) as well as higher ionic conductivity at 400 ◦C (3.09 × 10− 4 S⋅cm− 1 ). An attempt is made to correlate conductivity and catalytic oxidation in terms of oxygen mobility, vacancies, and superoxide formation.
Desenvolvimento de catalisadores heterogêneos a base de nióbio para oxidação do tioanisol.
(2022) Aguiar, Guilherme Carletti de; Silva, Adilson Cândido da; Fajardo, Humberto Vieira; Silva, Adilson Cândido da; Nogueira, André Esteves; Oliveira, Luiz Carlos Alves de
O estudo da oxidação do tioanisol é de grande importância, pois esse é modelo mais comum para se estudar oxidação de sulfetos orgânicos. Sua oxidação gera os grupos sulfóxido e sulfona, importantes precursores da indústria química, principalmente farmacêutica, pois são utilizados como blocos de construção de moléculas que possibilitarão a sintetização de uma ampla variedade de fármacos. Atualmente, a produção de ambos é realizada pelo método de oxidação aplicando diversos catalisadores (baixa atividade catalítica), tempos elevados e altas temperaturas. O que torna de enorme importância o desenvolvimento de catalisadores heterogêneos, que apresentam boa atividade catalítica e seletividade para obtenção de sulfóxidos e sulfonas. Os compostos de nióbio são importantes materiais encontrados tanto em associação com o elemento tântalo na forma de pegmatita e que após um processamento o nióbio é obtido na forma de Nb2O5, quanto sintético. Esses compostos despertam interesse para a aplicação em catálise heterogênea devido às características como a estabilidade química, baixa toxicidade e, principalmente, grande número de sítios ativos, como os grupos ácidos superficiais (Lewis e Brønsted), que podem ser modificados para formar espécies oxidantes denominados grupos peroxo-nióbio. Dessa forma, por serem bons candidatos para aplicação na catálise heterogênea, propôs-se a desenvolver um catalisador à base de nióbio com propriedades ácidas superficiais interessantes, através da síntese do oxihidróxido de nióbio (NbO2OH), de modo a compará-lo com outro composto a base de nióbio, o óxido de nióbio hidratado (Nb2O5∙nH2O) frente à reação de oxidação do tioanisol aos produtos metil fenil sulfóxido e metil fenil sulfona.Caracterizaram-se os materiais por adsorção/dessorção física de nitrogênio (BET), espectroscopia de infravermelho com piridina adsorvida (PyFTIR) e difração de raios-X (DRX).Os resultados obtidos nas caracterizações mostraram a obtenção de um catalisador com propriedades texturais interessantes, com elevada acidez superficial tanto de Lewis quanto de Brønsted. Para ambos os materiais, avaliaram-se as taxas de conversão variando a massa de catalisador, o tempo de reação, teor de H2O2, temperatura reacional e natureza do solvente. O NbO2OH apresentou conversões satisfatórias, sendo seu máximo de 92% em duas horas de reação, temperatura ambiente e utilizando H2O2 como agente oxidante.
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 da
A 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.
Direct decomposition of methane over Ni catalyst supported in magnesium aluminate.
(2012) Nuernberg, Giselle De Boit; Foletto, Edson Luiz; Campos, Carlos Eduardo Maduro de; Fajardo, Humberto Vieira; Carreño, Neftalí Lenin Villarreal; Probst, Luiz Fernando Dias
In this paper, the results obtained in the methane decomposition reaction promoted by a Ni catalyst supported on MgAl2O4 spinel are presented. The textural properties of the catalyst were investigated by X-ray diffraction (XRD), N2 adsorption/desorption isotherms (BET and BJH methods), thermogravimetric (TGA) and temperature-programmed reduction (TPR) analysis. The influence of the operating conditions employed on the methane decomposition was studied. According to the results, it was found that a N2:CH4 molar ratio of 7:1 and catalyst reduction temperature of 700 ◦C/1 h were the best conditions for methane decomposition. In addition, in the methane decomposition over Ni/MgAl2O4, multiwall carbon nanotubes were formed.
Effect of different synthesis methods on the textural properties of calcium tungstate (CaWO4 ) and Its catalytic properties in the toluene oxidation.
(2018) Alencar, Lorena Dariane da Silva; Lima, Naiara Arantes; Mesquita, Alexandre; Probst, Luiz Fernando Dias; Batalha, Daniel Carreira; Rosmaninho, Marcelo Gonçalves; Fajardo, Humberto Vieira; Bernardi, Maria Inês Basso
Calcium tungstate (CaWO4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FE-SEM images showed particles with rounded morphology and particles in clusters dumbbells-like shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples.
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 Alejandra
This 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.
Estudo da oxidação da anilina utilizando catalisadores de ferro.
(2020) Amaral, Nathália Braga; Silva, Adilson Cândido da; Rosmaninho, Marcelo Gonçalves; Silva, Adilson Cândido da; Moura, Flávia Cristina Camilo; Fajardo, Humberto Vieira
Neste trabalho foram sintetizados cinco materiais com diferentes metodologias de síntese dos óxidos e oxi-hidróxidos de ferro, hematita e goethita. Destes cinco, quatro catalisadores foram sintetizados pelo método microemulsão, dois óxidos de ferro, e dois óxido-hidróxido de ferro. Em dois destes materiais a dissolução do agente percursor, nitrato férrico nona hidratado, ocorreu na microemulsão (síntese 1) e em dois na solução aquosa (síntese 2). Foram então obtidos materiais denominados de HmS1, HmS2, GtS1 e GtS2. Para efeito de comparação e continuidade do estudo foi sintetizada uma hematita pelo método de decomposição térmica, denominada de Hm. Estes catalisadores foram caracterizados segundo suas características físicas e químicas, morfológicas e texturais, pelas técnicas de difração de raio-x, espectroscopia Mössbauer, isotermas de adsorção e dessorção de nitrogênio e microscopia eletrônica de varredura. Os materiais sintetizados por microemulsão obtiveram elevada área superficial específica, sendo que os materiais da síntese 1 (microemulsão reversa), alcançaram área de 27 m2 g -1 e 257 m2 g -1 para hematita e goethita, respectivamente. Estes catalisadores foram aplicados em ensaios catalíticos oxidando anilina em fase líquida. Foram realizados estudo cinético, de variação de volume de peróxido de hidrogênio, de efeito de diferentes solventes, e por fim reuso destes catalisadores. Observou-se a seletividade a azoxibenzeno para catalisadores de goethitas e à nitrosobenzeno para catalisadores de hematitas.
Feasible and clean solid-phase synthesis of LiNbO3 by microwave- induced combustion and its application as catalyst for low- temperature aniline oxidation.
(2018) Carreño, Neftalí Lenin Villarreal; Deon, Vinícius Gonçalves; Silva, Ricardo M.; Santana, Luiza R.; Pereira, Rodrigo M.; Orlandi, Marcelo Ornaghi; Ventura, Wellington Martins; Dias, Anderson; Taylor, Jason Guy; Fajardo, Humberto Vieira; Mesko, Márcia Foster
In this work, a feasible, fast, clean and efficient microwave-induced combustion method for direct synthesis of LiNbO3 in solid phase was developed. X-ray powder diffraction studies showed that quasi-pure Li−Nb−O phases, such as LiNbO3 and Li3NbO4, or mixtures of LiNbO3, Li3 NbO4 and LiNb3O8, could be successfully synthesized. The resulting powders were efficiently applied as catalysts under ambient conditions in the oxidation process of aniline using hydrogen peroxide as oxidant. The proposed method was performed in a commercial system using high-pressure quartz vessels, which allowed safe control of the reactions−that usually occurs in less than 1 min. The results showed that the reaction conditions as well as the structural and morphological characteristics of the catalyst influenced the aniline oxidation process. Therefore, the present method for the preparation of LiNbO3 described herein, displayed many advantages when compared to conventional combustion methods, such as the physical characteristics of the obtained compound. Moreover, this new approach is considerably faster, safer and cleaner than other traditional procedures described in literature for LiNbO3 synthesis. This new microwave-induced combustion method is less time-consuming, saves energy, as well as affording the stoichiometric formation of inorganic particles.
Gadolinium-doped cerium oxide nanorods : novel active catalysts for ethanol reforming.
(2010) Godinho, Mario; Gonçalves, Rosana de Fátima; Leite, Edson Roberto; Ratmann, Cristiane Wienke Raubach; Carreño, Neftalí Lenin Villarreal; Probst, Luiz Fernando Dias; Longo, Elson; Fajardo, Humberto Vieira
The gadolinium-doped ceria nanorods (Gd0.2 Ce0.8O2-x) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd0.2 Ce0.8O2-x nanorods were more catalytically active than commercial CeO2 in the ethanol reforming reaction.
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 Paim
Noble-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.
Hydrogen production from ethanol steam reforming over Ni/CeO2 nanocomposite catalysts.
(2007) Fajardo, Humberto Vieira; Probst, Luiz Fernando Dias; Carreño, Neftalí Lenin Villarreal; Garcia, Irene Teresinha Santos; Valentini, Antoninho
The organic polymer chitosan was used as the polymeric precursor for the synthesis of Ni/CeO2 nanocomposite catalysts. The materials were characterized by N2 physisorption, H2 chemisorption, AA, XRD, TGA, TPR, SEM and TEM analyses. The catalysts provide very good reactivity in ethanol steam reforming compared to the conventional Ni/CeO2 catalyst prepared by the impregnation method using a commercial support. High hydrogen selectivity (>75%) was obtained on Ni/CeO2 catalysts by operating at a temperature range of 325–500 C and a H2O/ C2H5OH molar ratio of 3. It was verified that the catalytic behavior could be influenced depending on the experimental conditions employed.
Influence of Nb2O5 grown on SrTiO3 nanoseeds in the catalytic oxidation of thioanisole.
(2022) Riemke, Fábio Calcagno; Ücker, Cátia Liane; Carreño, Neftalí Lenin Villarreal; Cava, Sergio da Silva; Teixeira, Moisés Paulo; Fajardo, Humberto Vieira; Taylor, Jason Guy; Silva, Marcio José da; Batalha, Daniel Carreira; Ratmann, Cristiane Wienke Raubach
There is a growing interest on the reach for new environmentally friendly catalysts especially solid metal oxides. The functional properties of SrTiO3 (STO) and its combination with other materials seem promising to yield catalytic reactions. In this sense, niobium oxides, particularly its most stable form Nb2O5, have showing a stunning compatibility with SrTiO3 arrays producing applicable compounds for high yield catalytic benchmarks. Here we investigate the yield of SrTiO3 and the activity of SrTiO3/Nb2O5 catalytic system in the oxidation process of thioanisole. This catalyst was synthesized through microwave assisted hydrothermal process in which Nb2O5 react with SrTiO3 nanoseeds in solution. The SrTiO3 nanoseeds seem to have induced a long-range order monoclinic array for the Nb2O5 stoichiometry for a certain period after which a disordered nanocrystalline phase for Nb2O5 was formed. Although this Nb2O5 growth on SrTiO3 arrays has already been shown in the literature, it differs from the results expected for a Nb2O5 synthesis using the MAH method, which will only produce nanocrystalline matrices at the temperature of 130 ◦C in a 15-min synthesis. The SrTiO3/Nb2O5 catalyst demonstrated to be highly efficient in thioanisole oxidation with hydrogen peroxide.