Navegando por Autor "Ventura, Wellington Martins"

Agora exibindo 1 - 4 de 4

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.
Low temperature liquid phase catalytic oxidation of aniline promoted by niobium pentoxide micro and nanoparticles.
(2017) Ventura, Wellington Martins; Batalha, Daniel Carreira; Fajardo, Humberto Vieira; Taylor, Jason Guy; Marins, Natália Hadler; Noremberg, Bruno S.; Tański, Tomasz; Carreño, Neftalí Lenin Villarreal
A microwave-assisted hydrothermal method was employed to synthesis Nb2O5 (niobium pentoxide) nanoparticles and the effects of synthesis conditions on the physical-chemical properties were evaluated. The catalytic activity of the prepared samples in the liquid phase oxidation of aniline with aqueous hydrogen peroxide as oxidizing agent was also studied. The nanoparticles showed hexagonal structure and rounded shape covered by nanoneedles. The results evidenced high catalytic activity with total conversion of aniline at ambient condition. Aniline conversion and product selectivities depended on the experimental parameters, particularly the oxidizing agent concentration, the nature of the solvent, type of the catalyst and reaction time.
Preparação de catalizadores heterogêneos a base de Nb2O5 e CeO2 para oxidação da anilina em fase líquida.
(2017) Ventura, Wellington Martins; Fajardo, Humberto Vieira; Taylor, Jason Guy; Fajardo, Humberto Vieira; Bellido, Jorge David Alguiar; Rocha, Kelly Alessandra da Silva
O presente trabalho consiste na preparação, caracterização e testes de avaliação do comportamento dos catalisadores de Óxido de Nióbio (V) é Óxido de Cério (IV) na reação de oxidação da anilina em fase líquida. As obtenções dos sólidos foram conduzidas utilizando o método hidrotérmico assistido por micro-ondas, para o Nb2O5, e o método de complexação metal-quitosana, para o CeO2. Os efeitos das condições de síntese sobre as propriedades físico-químicas dos catalisadores foram avaliados. Os resultados obtidos através das caracterizações físico-químicas e dos ensaios catalíticos mostraram que as metodologias adotadas para a preparação dos catalisadores proporcionaram a obtenção de materiais com interessantes propriedades texturais e catalíticas, comparativamente aos materiais análogos disponíveis comercialmente. Os catalisadores se mostraram ativos frente ao processo de oxidação da anilina em fase líquida, usando o peróxido de hidrogênio como agente oxidante. Os resultados evidenciaram alta atividade catalítica, em alguns casos com conversão total da anilina em condições reacionais brandas (temperatura e pressão ambiente). A atividade e a seletividade dos catalisadores variaram em função da natureza do catalisador, quantidade de agente oxidante, tipo de solvente e tempo de reação empregados. Sobre os catalisadores de Nb2O5, os principais produtos formados foram a fenilhidroxilamina e nitrobenzeno, enquanto sobre os catalisadores de CeO2, nitrosobenzeno e azoxibenzeno foram os produtos reacionais majoritários.
Synthesis of a benzannulated pyrrolizidine by a copper-catalyzed intramolecular a-arylation reaction.
(2014) Araújo, Flavia Magalhães; Ventura, Wellington Martins; Taylor, Jason Guy
A synthetic route to the pyrrolo[1,2-a]indole ring system (benzannulated pyrrolizidine) involving a base-induced intramolecular aza-Michael reaction as the key C N bond-forming penultimate step, followed by a Cu-catalyzed intramolecular a-arylation reaction, to provide the tricyclic framework over six steps is described.