Desenvolvimento de catalisadores de ródio e cobalto para a reforma a vapor do etanol.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The development of technologies based on the use of biofuels has taken the attention of the scientific community, due to the current dependence on fossil fuels, which results in an increase of air pollution. This pollution increase is related to public health problems and climate changes. In this context, the use of fuel cells moved by hydrogen is a mean of producing energy in a clean way, once the residual product of the cell operation is water. The hydrogen to be used in this equipment can be obtained from the reaction of hydrocarbons or alcohols with water vapor in the steam reforming process. Therefore, the present work is based on the development of catalysts for the production of hydrogen from the ethanol steam reforming. While the process involving hydrocarbons contributes to the increase of air pollution, once that large amounts of carbon dioxide are produced, the use of ethanol contributes to solve environmental problems because it can be produced from sugar cane and other crops and carbon dioxide produced is consumed during the growth of biomass. In this work, there were synthesized monometallic and bimetallic catalysts of rhodium (0.5%) and cobalt (1%) supported on aluminum oxide, magnesium oxide and on a mixed material containing aluminum and magnesium, obtained from the thermal decomposition of a hydrotalcite. The samples were characterized by chemical analysis, thermogravimetry, differential thermal analysis, Fourier transformed infrared spectroscopy, X rays diffraction, specific surface area measurements, temperature programmed reduction and Fourier transformed infrared spectroscopy using carbon monoxide as probe molecule. The catalysts were tested in the ethanol steam reforming reaction at 500, 600 and 700 C. The use of hydrotalcite as precursor produced catalysts with high specific surface area but with low resistance to sintering and phase change. It was noted that the rhodium containing catalysts were active and selective to hydrogen while the cobalt monometallic ones did not show activity, what was attributed to the low percentage of cobalt in the solids and to the formation of species with high reduction temperature, such as the solid solution CoO-MgO and the spinel CoAl2O4. The results showed that with increasing reaction temperature, higher ethanol conversions are obtained and the formation of by-products such as ethylene, acetaldehyde and ethyl ether is inhibited. Moreover, the acid-base properties of the supports showed influence on the selectivity of the catalysts to the gas products during the ethanol steam reforming. The catalysts containing magnesium showed low selectivity to ethylene, while those based on aluminum oxide showed high selectivities to this alcene.

ASSUNTO(S)

ethanol hydrotalcite ródio óxidos hydrogen hidrotalcita cobalto cobalt hidrogênio rhodium oxides fisico-quimica etanol

ACESSO AO ARTIGO

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