Different crystal-forms of one-dimensional MnO2 nanomaterials for the catalytic oxidation and adsorption of elemental mercury
2015
Xu, Haomiao | Qu, Zan | Zhao, Songjian | Mei, Jian | Quan, Fuquan | Yan, Naiqiang
MnO2 has been found to be a promising material to capture elemental mercury (Hg0) from waste gases. To investigate the structure effect on Hg0 uptake, three types of one-dimensional (1D) MnO2 nano-particles, α-, β- and γ-MnO2, were successfully prepared and tested. The structures of α-, β- and γ-MnO2 were characterized by XRD, BET, TEM and SEM. The results indicate that α-, β- and γ-MnO2 were present in the morphologies of belt-, rod- and spindle-like 1D materials, respectively. These findings demonstrated noticeably different activities in capturing Hg0, depending on the surface area and crystalline structure. The performance enhancement is in the order of: β-MnO2<γ-MnO2<α-MnO2 at 150°C. The mechanism for Hg0 removal using MnO2 was discussed with the help of results from H2-TPR, XPS and Hg0 removal experiments in the absence of O2. It was determined that the oxidizability of three forms of MnO2 increased as follows: β-MnO2<γ-MnO2<α-MnO2. The mechanism for Hg0 capture was ascribed to the Hg0 catalytic oxidation with the reduction of Mn4+→Mn3+→Mn2+. Furthermore, the interaction forces between mercury and manganese oxide sites are demonstrated to increase in the following order: β-MnO2<γ-MnO2<α-MnO2 based on the desorption tests.
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