Abstract: Cerium modified semi coke adsorbent (Ce/SC) was prepared by impregnation method and a bench-scale fixed bed reactor was used to study the effect of H₂O vapor and α-Fe₂O₃ on elemental mercury removal efficiency over Ce/SC. Characterizations of X-ray powder diffraction (XRD), Hydrogen temperature programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the mechanism of elemental mercury removal.The adsorption results showed that H₂O had a negative effect on the oxidation activity of the adsorbent. H₂O can be dissociated on the surface of CeO₂ with partial lattice oxygen transformation into Ce-OH functional groups which led to the decrease of its oxidation activity and thus resulted in the inhibitory effect of mercury removal efficiency. The addition of α-Fe₂O₃ had no significant effect on mercury removal over Ce/SC. The mercury removal efficiency of Ce/SC was decreased when the water vapor and α-Fe₂O₃ existed simultaneously. However, the decrease rate was much lower than that of water vapor conditions alone mainly due to the interaction between water vapor and α-Fe₂O₃ increased the content of the surface chemical adsorbed oxygen and thus the oxidation activity and elemental mercury removal performance of Fe₂O₃were promoted.