Estudo das propriedades físicas e químicas de esferas compostas de SiO2-Al2O3, sintetizadas pelo método híbrido empregando-se os polímeros quitosana e pva (álcool polivinílico).

Abstract

The science of materials provides the study and understanding of the properties of materials and their use in the most diverse needs of our society. Nowadays it is perceived the great need of sources of clean energy in substitution to the fossil fuels, in this way a great quantity of scientific works directed for this purpose is observed. It is reported the development of materials by the most diverse methods of synthesis, which causes materials with distinct properties and extremely interesting catalysis. An important class of materials applied in the production of clean energy with the aid of catalysts are the aluminosilicates, these materials present acidic sites that are very important in the reactions of dehydration and cracking, besides providing high surface area. In this way, spheres composed of aluminum and silicon oxides were synthesized using the chitosan polymer as a structure and porosity conductor. The influence of the partial replacement of the chitosan mass with polyvinyl alcohol in relation to the morphological properties of the spheres was studied. Additionally, the effect of the presence of sodium silicate on the acid and morphological properties of the aging medium of the spheres was studied. For this, different alkaline solutions (NH4OH or Na2SiO3) were used. In order to evaluate the behavior of the material synthesized as catalytic support, it was impregnated with iron oxide. Obtaining a material with great possibilities of application in diverse reactions. The samples were characterized with different techniques, such as: (XRF) X-ray fluorescence, (XRD) X-ray diffraction, adsorption isotherm and N2 desorption, Infrared Spectroscopy (IR), CO2 Desorption at Programmed Temperature TPD-CO2), Pyridine Adsorption Isotherm, Thermogravimetric Analysis (TG), Differential Thermogravimetric Analysis (DTA) and catalytic test for ethanol dehydration. The replacement of chitosan (Qts) by polyvinyl alcohol (PVA) promotes significant changes in surface area and pore volume. A similar effect was observed when Na2SiO3 solution was used. The diffractograms of the samples have amorphous characteristics, even after calcination at 600oC. The ethanol dehydration reaction was used for the purpose of analyzing the acidity of the material. It was observed that the conversion is affected by the progressive decrease of the surface area. The major selectivity observed was diethyl ether; but the selectivity to the ethylene product increases with the replacement of the Qts polymer with PVA, which promotes a higher acidity in the samples.