Navegando por Autor "Camargo, Pedro Henrique Cury"
Agora exibindo 1 - 4 de 4
Resultados por página
Opções de Ordenação
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 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 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 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 performances