The concern regarding the environment, especially with gases emission by burning fossil fuels, and the increase of energy demand have influenced the development of cleaner and more efficient technologies for energy generation. In this context, studies involving hydrogen and fuel cells are remarkable among future technologies due to its great commercial potential and high energetic efficiency of the process. Theoretically speaking, hydrogen production from biomass or liquids derived from biomass such as ethanol can be considered a carbon emission free process since all the carbon dioxide produced can be recycled by the plants using sun power [1]. Obtaining hydrogen from ethanol might be carried out through catalytic reaction of ethanol steam reforming: (C2H5OH + 3H2O „_ 6H2 + 2CO2) [2-4]. This pathway is extremely attractive and capable of solving many questions involved in hydrogen storage and delivery infrastructure, allowing a well spread production strategy [1].
This work presents an evaluation of performance of the 0.5% Pd-0.5% Ru/Nb2O5-TiO2 catalyst in the reaction between ethanol and steam at temperatures of 573, 648 and 723 K under atmospheric pressure. The catalysts tests were carried out with H2O/C2H5OH molar ratio equals to 10/1 and W/Feth equals to 17.16 (gcat h/mol). The feeding of the reagent mixture was carried out in liquid phase without the presence of inert gases and a packed bed tubular reactor (7g) built in stainless steel (18 cm X 2.1 cm i.d.) was used to obtain the data under closer conditions to the necessary ones for industrial application. Prepared by impregnation from alcoholic solutions of chloride salts precursors of Pd and Ru, the catalyst was characterized by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), textural analysis by adsorption/desorption isotherms of N2 at 77 K, temperature programmed reduction (TPR) and temperature programmed desorption of NH2 (TPD-NH3).
The catalytic tests results reveal that the increase in reaction temperature causes the decrease of catalytic activity to ethanol conversion. When the hydrogen production process was carried out at 573 K, it was possibly dominated by reactions of ethanol decomposition and partly of steam reforming reactions and ethanol dehydrogenation. At 648 and 723 K, the efficiency decrease for hydrogen production occurs due to catalytic activity increase for ethanol dehydration and dehydrogenation reactions causing the increase of acetaldehyde and ethane selectivity respectively. Under all temperature conditions evaluated H2, CO2, CH4, CO, C2H4, C2H6, C2H4O, (C2H5)2O and coke, were produced from simultaneous reactions identified as dehydrogenation, dehydration, decomposition and ethanol steam reforming.
References
[1] H. Song, L. Zhang, R. B. Watson, D. Braden, U. S. Ozkan, Cat. Today 129 (2007) 346.
[2] D. R. Sahoo, S. Vajpai, S. Patel, K. K. Pant, Chem. Eng. J. 125 (2007) 139.
[3] A. Casanovas, J. Llorca, N. Homs, J. L. G. Fierro, P. R. de la Piscina, J. Mol. Cat. A: Chem. 250 (2006) 44.
[4] B. Zhang, X. Tang, Y. Li, W. Cai, Y. Xu, W. Shen, Cat. Commun. 7 (2006) 367
