Made available in DSpace on 2014-12-17T14:06:55Z (GMT). No. of bitstreams: 1 AnaPP.pdf: 5176837 bytes, checksum: 9d8890c4a2dd055dfe7d581f34a7f4e8 (MD5) Previous issue date: 2011-01-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nickel-based catalysts supported on alumina have been widely used in various reactions to obtain synthesis gas or hydrogen. Usually, higher conversion levels are obtained by these catalysts, however, the deactivation by coke formation and sintering of metal particles are still problems to be solved. Several approaches have been employed in order to minimize these problems, among which stands out in recent years the use of additives such as oxides of alkali metals and rare earths. Similarly, the use of methodologies for the synthesis faster, easier, applicable on an industrial scale and to allow control of the microstructural characteristics of these catalysts, can together provide the solution to this problem. In this work, oxides with spinel type structure AB2O4, where A represents divalent cation and B represents trivalent cations are an important class of ceramic materials investigated worldwide in different fields of applications. The nickel cobaltite (NiCo2O4) was oxides of spinel type which has attracted considerable interest due to its applicability in several areas, such as chemical sensors, flat panel displays, optical limiters, electrode materials, pigments, electrocatalysis, electronic ceramics, among others. The catalyst precursor NiCo2O4 was prepared by a new chemical synthesis route using gelatine as directing agent. The polymer resin obtained was calcined at 350?C. The samples were calcined at different temperatures (550, 750 and 950?C) and characterized by X ray diffraction, measurements of specific surface area, temperature programmed reduction and scanning electron microscopy. The materials heat treated at 550 and 750?C were tested in the partial oxidation of methane. The set of techniques revealed, for solid preparations, the presence of the phase of spinel-type structure with the NiCo2O4 NixCo1-xO solid solution. This solid solution was identified by Rietveld refinement at all temperatures of heat treatment. The catalyst precursors calcined at 550 and 750?C showed conversion levels around 25 and 75%, respectively. The reason H2/CO was around 2 to the precursor treated at 750?C, proposed reason for the reaction of partial oxidation of methane, one can conclude that this material can be shown to produce synthesis gas suitable for use in the synthesis Fischer-Tropsch process / Catalisadores a base de n?quel suportados em alumina, t?m sido amplamente empregados nas diversas rea??es para obten??o de g?s de s?ntese ou hidrog?nio. Normalmente, altos n?veis de convers?o s?o obtidos por estes catalisadores, entretanto, a desativa??o por forma??o de coque e sinteriza??o das part?culas met?licas s?o ainda problemas a serem solucionados. Diversas abordagens t?m sido empregadas com a finalidade de minimizar estes problemas, dentre as quais tem se destacado nos ?ltimos anos a utiliza??o de aditivos como ?xidos de metais alcalinos e metais terras raras. Paralelamente, o uso de metodologias de s?nteses mais r?pidas, f?ceis, aplic?veis em escala industrial e que permitam o controle das caracter?sticas microestruturais destes catalisadores, pode em conjunto, prover a solu??o para este problema. Neste trabalho, ?xidos com estrutura tipo espin?lio AB2O4, onde A representa c?tions divalentes e B representa c?tions trivalentes, s?o uma classe importante de materiais cer?micos mundialmente investigados em diferentes campos de aplica??es. As cobaltitas de n?quel (NiCo2O4) s?o ?xidos do tipo espin?lio que tem atra?do consider?vel interesse devido a sua aplicabilidade em diversas ?reas, como em sensores qu?micos, monitores de tela plana, limitadores ?pticos, materiais para eletrodos, pigmentos, eletrocat?lise, cer?micas eletr?nicas, entre outras. O precursor catal?tico NiCo2O4 foi preparado por uma nova rota de s?ntese qu?mica usando a gelatina como agente direcionador. A resina polim?rica obtida foi tratada termicamente a 350?C. As amostras foram calcinadas em diferentes temperaturas 550, 750 e 950?C e caracterizadas por difra??o de raios X, medidas de ?rea superficial espec?fica, redu??o a temperatura programada e microscopia eletr?nica de varredura. Os materiais tratados termicamente a 550 e 750?C foram testados na oxida??o parcial do metano. O conjunto de t?cnicas revelaram, nos s?lidos preparados, a presen?a da fase de estrutura espin?lio do tipo NiCo2O4 juntamente com a solu??o s?lida NixCo1-xO. Esta solu??o s?lida foi identificada atrav?s do refinamento Rietveld em todas as temperaturas de tratamento t?rmico. Os precursores catal?ticos calcinados a 550 e 750?C apresentaram n?veis de convers?o em torno de 25 e 75%, respectivamente. A raz?o H2/CO foi em torno de 2 para o precursor tratado a 750?C, raz?o proposta pela rea??o de oxida??o parcial do metano, pode-se concluir que este material pode ser indicado para produzir g?s de s?ntese adequado para ser utilizado na s?ntese de Fischer-Tropsch

The main objective of nanotechnology is to build self-powered nanosystems that are ultrasmall in size, exhibit super sensitivity, extraordinary multi functionality, and extremely low power consumption. As we all know that 21st century has brought two most important challenges for us. One is energy shortage and the other is global warming. Now to overcome these challenges, it is highly desirable to develop nanotechnology that harvests energy from the environment to fabricate self-power and low-carbon nanodevices. Therefore a self-power nanosystem that harvests its operating energy from the environment is an attractive proposition. This is also feasible for nanodevices owing to their extremely low power consumption. One advantageous approach towards harvesting energy from the environment is the utilization of semiconducting piezoelectric materials, which facilitate the conversion of mechanical energy into electrical energy. Among many piezoelectric materials ZnO has the rare attribute of possessing both piezoelectric and semiconducting properties. But most applications of ZnO utilize either the semiconducting or piezoelectric property, and now it’s time to fully employ the coupled semiconducting-piezoelectric properties to form  the basis for electromechanically coupled nanodevices. Since wurtzite zinc oxide (ZnO) is structurally noncentral symmetric and has the highest piezoelectric tensor among tetrahedrally bonded semiconductors, therefore it becomes a promising candidate for energy harvesting applications. ZnO is relatively biosafe and biocompatible as well, so it can be used at large scale without any harm to the living environment. The synthesis of another transition metal oxide known as Co3O4 is also important due to its potential usage in the material science, physics and chemistry fields. Co3O4 has been studied extensively due to low cost, low toxicity, the most naturally abundant, high surface area, good redox, easily tunable surface and structural properties. These significant properties enable Co3O4 fruitful for developing variety of nanodevices. Co3O4 nanostructures have been focused considerably in the past decade due to their high electro-chemical performance, which is essential for developing highly sensitive sensor devices. I started my work with the synthesis of ZnO nanostructures with a focus to improve the amount of harvested energy by utilizing oxygen plasma treatment. Then I grow ZnO nanorods on different flexible substrates, in order to observe the effect of substrate on the amount of harvested energy. After that I worked on understanding the mechanism and causes of variation in the resulting output potential generated from ZnO nanorods. My next target belongs to an innovative approach in which AFM tip decorated with ZnO nanorods was utilized to improve the output energy. Then I investigated Co3O4 nanostructures though the effect of anions and utilized one of the nanostructure to develop a fast and reliable pH sensor. Finally to take the advantage of higher degree of redox chemistry of NiCo0O4 compared to the single phase of nickel oxide and cobalt oxide, a sensitive glucose sensor is developed by immobilizing glucose oxidase. However, there were problems with the mechanical robustness, lifetime, output stability and environmental adaptability of such devices, therefore more work is going on to find out new ways and means in order to improve the performance of fabricated nanogenerators and sensors.