Produção de hidrogênio a partir da decomposição termoquímica da água

Abstract

The feasibility of using hydrogen as energy vector has been intensified since the combustion of H2 produces only water and energy. One possible route for obtaining H2 is from the Thermochemical water splitting cycles using two or more steps. Thus, the aim of this work was to study the production of hydrogen from thermochemical decomposition of water in two stages, using perovskite oxides LaxSr(1-x)FeO3 and LayCe(1-y)FeO3. The catalysts were prepared by sol-gel method and characterized using the following techniques: BET surface area, X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Temperature Programmed Reduction (TPR) and Raman spectroscopy. The oxidation state of iron was determined by titration technique. The performance of perovskites in thermochemical water splitting was evaluated using reduction and oxidation cycles with water. In the characterization, BET analysis showed that partial substitution of La by a second metal, such as Ce or Sr, did not cause significant changes in surface area. XRF data showed that the measured composition is very close to the theoretical content calculated for the formation of the perovskites. The results of XRD and Raman spectroscopy showed that the synthesized materials have a well defined crystalline structure characteristic of perovskites. TPR analyses showed that only a small part of the material was reduced and the structure of the perovskite phase remained as predominant. The tests with oxidation and reduction cycles showed that all samples had higher H2 production in the second cycle, and the catalyst La0,95Ce0,05FeO3 obtained the best result, probably because of the good redox properties of Ce. XRD analysis of the perovskite LaFeO3 performed after two redox cycles, showed that the structure of the material did not changed significantly. This indicates that LaFeO3 perovskite-type catalysts are materials with good potential to perform the reactions of decomposition of water using oxidation and reduction cycles in order to produce hydrogen.