Synthesis of CeO2-modified activated carbon spheres by grafting and coordinating reactions for elemental mercury removal

Series of resin-based activated carbon spheres with well-dispersed CeO2 particles inside and high surface area were successfully prepared by the grafting of MMA and coordinating reactions of cerium(III) nitrate salt and steam activation. N2 adsorption isotherms, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction-meter and X-ray photoelectron spectroscopy were applied to study the textural and surface characteristics of the obtained activated carbon spheres, and the Hg0 removal performances were evaluated in a fixed bed reactor. The experimental results indicated that pore structure, surface chemical properties and Hg0 removal ability of activated carbon spheres were observably improved after the modification of grafting and coordinating reactions. The optimal cerium(III) nitrate loading value, reaction temperature and O2 content were 7%, 150 °C and 5%, respectively. Moreover, SO2 showed an obvious inhibitory effect on the Hg0 removal efficiency in the absence of O2, while it facilitated the Hg0 removal in the presence of O2. Nitrogen monoxide promoted the Hg0 removal with or without O2, while water vapor inhibited the Hg0 removal over ACS-M-7%Ce. In addition, both of stable removal performance and excellent recycling ability were shown for ACS-M-7%Ce in ten cycles. The Hg0 removal mechanism analysis indicated that introduced CeO2 significantly promoted the Hg0 removal ability of ACS-M-7%Ce by generating the active species (such as C=O or C–O) and the lattice oxygen through the Ce4+/Ce3+ redox couple, and catalytically oxidized Hg0 into HgO.