Efeito do método de preparação nas propriedades de catalisadores anódicos de céria para células a combustível de óxido sólido

Abstract

Considering the current need for energy, in all aspects of modern life, it is essential to meet the growing demands within a perspective of sustainability of the planet. Fossil sources used for energy supply cause severe environmental impacts, making the search for renewable energy sources urgent, as well as the efficient generation of energy. Among the technologies proposed to overcome these difficulties, solid oxide fuel cells (SOFCS) are recognized as the most suitable for large-scale clean energy production, especially in remote places. These devices are versatile and have the advantage of using different fuels, including biogas, a renewable fuel made up of methane and carbon dioxide. This gaseous mixture can be fed directly in the SOFC anode, over a suitable catalyst and produce hydrogen and syngas, reactants of the electrochemical reaction, which will produce electricity. In this work, nickel catalysts (10% w/w) supported on cerium oxide, doped or not, with gadolinium (10% w/w), prepared by different methods, were studied in order to obtain catalysts for dry reforming ( reaction between methane and carbon dioxide), directly at the anode of the SOFC. Sol-gel, combustion and Marcilly methods were used to obtain the supports that were impregnated with nickel nitrate solutions (10% m). The supports and catalysts were characterized by X-ray diffraction, temperature programmed reduction, Raman spectroscopy, UV-Visible spectroscopy, Fourier transform infrared spectroscopy, temperature programmed desorption with ammonia and transmission electron microscopy. The formation of the cubic phase of cerium oxide was observed for all samples, regardless of the preparation method and the presence of gadolinium. Nickel oxide was identified, but gadolinium formed a solid solution with cerium oxide. In the lattice of this oxide, gadolinium induced the formation of oxygen vacancies, increasing the mobility of ions in the solid and facilitating the reduction process. This effect was more pronounced in samples prepared by the Marcilly and combustion methods. The preparation method decreased the interaction of nickel with the support in the combustion<Marcilly<sol-gel order, making difficult nickel reduction, regardless of the presence of gadolinium. In all cases, only the formation of weak and moderate acid sites was observed, related to structural defects, which favor the storage of oxygen with a high capacity for electron donation. The Marcilly method led to the formation of weaker acid sites, in relation to the materials obtained by the other methods. The average particle sizes of the catalysts were dependent on the preparation method in the order Marcilly<combustion<<sol-gel. Considering the properties generated in the solids as a result of the different methods, the gadolinium-containing catalyst prepared by the Marcilly method is the most promising to perform dry reforming at the anode of a SOFC. It has the lowest nitrate content, the smallest particles size and the lowest acidity, which are suitable properties for this application.