Oxidation Reduction Behavior of Iron-Bearing Olivines (FexMg1-x)2SiO4 Used as Catalysts for Biomass Gasification

Natural iron-bearing olivines (FexMg1-x)2SiO4 have been recognized as one of the most promising tar-cracking catalytic materials for fluidized bed biomass gasification to produce syngas (H2 + CO). Iron present in the olivine significantly influences its catalytic activity. However, the Fe0-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 57Fe Mossbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-progr...