The evolution of Fe and Fe-Ca catalysts during char catalytic hydrogasification

The evolution of Fe and Fe-Ca catalysts during char catalytic hydrogasification was investigated in a pressurized fixed-bed reactor. The effects of Fe and Fe-Ca catalysts on CH4 yield and CH4 formation rate were studied. The change of the catalysts and char was also characterized by means of the transmission electron microscopy (TEM), X-ray diffraction (XRD), Temperature-programmed reduction (TPR), etc. The relationship between the CH4 formation rate and the ratio of Fe3C to Fe was discussed to identify the rate determining step, as well as possible reaction mechanism. The results show that the role of calcium on char catalytic hydrogasification is not only dispersion of iron-group metals and desulphurization but also promotes the reduction of metal iron as well as carburization reaction. As for Fe-Ca catalyzed case, a negative correlation between V-CH4 and ratio of Fe3C to Fe was found during hydrogasification. The larger the proportion of Fe3C is, the slower the methane formation rate becomes. These results indicate that iron carbide is a stable intermediate product of catalytic hydrogasification. The hydrogenation of iron carbide to form methane is the rate determining step for Fe catalyzed hydrogasification.