Oxidation Reduction Behavior of Iron-Bearing Olivines (Fe_xMg_1-x)₂SiO₄ Used as Catalysts for Biomass Gasification

Natural iron-bearing olivines (Fe x Mg 1 - x ) 2 SiO 4 have been recognized as one of the most promising tar-cracking catalytic materials for fluidized bed biomass gasification to produce syngas (H 2 + CO). Iron present in the olivine significantly influences its catalytic activity. However, the Fe 0 -active phase cannot be obtained by the reduction of olivine under the catalyst working conditions. A better understanding of olivine's behavior in oxidizing−reducing conditions is crucial for control of its catalytic properties. In this paper, we have demonstrated how the oxidation of iron-bearing olivines leads to the formation of reducible iron oxides dispersed in the iron-depleted olivine matrix. The choice of oxidation−reduction conditions permits us to control the amount of iron extracted from the olivine structure. The mechanism of the oxidation−reduction behavior of a natural olivine has been studied by 57 Fe Mössbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction (TPR).