resumo
Energy storage Natural minerals such as olivines, (Fe,Mg)2SiO4 have been proposed as potential low cost catalyst for biomass gasification. However, their mechanisms are still poorly understood. Thus, the present work is focused on synthesis of fayalite (Fe2SiO4), to allow detailed studies of effects of impurities and changes in composition, or other relevant factors such as structural and microstructural features, oxidation states, etc., which may be determined by thermochemical processing conditions or natural genesis. Thermodynamic predictions were performed to assess expected thermochemical conditions required for synthesis of Fe2SiO4, and the corresponding stability windows (redox and aFe/aSi activity ratio) in prospective catalytic operation, by analogy with methods proposed for Ni-based catalysts [1]. These predictions show that synthesis requires controlled reducing conditions, and also indicated that these redox conditions may be provided by CO/CO2 or H2/H2O redox pairs. However, this could not be achieved by using silica and iron oxides as precursors. Thus, one developed an alternative synthesis method based on high temperature powder reaction between silicon carbide and hematite, as described by: 〖SiC+Fe〗_2 O_3+2CO_2→〖Fe〗_2 〖SiO〗_4+3CO (1) This indicates that controlled fluxes of a CO2-based gas may correct the oxygen deficiency in the precursor mixture while yielding also the CO:CO2 ratio required to adjust required redox conditions. Successful synthesis of single phase catalysts was achieved by optimizing the thermal cycling under a continuous flow of dry CO2. Preiminary catalytic testing demonstrated that these synthetic Fe2SiO4 catalyst suppresses tar impurities in biomass derived gases and also promotes reforming reactions. Suitable control of thermal schedules also allow one to obtain binary Fe2SiO4+Fe3O4 catalyst or ternary Fe2SiO4+Fe3O4+Fe. In addition, the reducing character of SiC may also be used to prepare Fe2SiO4+FeTiO3 catalysts by reaction of ternary precursor mixtures.
autores
L.Ruivo1, R.Pinto, L. Tarelho, A.Yaremchenko, J. Frade
nossos autores
