Preparation of Cu-Mn and Cu-Mn-Ce Oxide/Mesoporous Silica via Silicate Exfoliation for Removal of NO and Hg0

摘要

Cu-Mn and Cu-Mn-Ce oxide-incorporated mesoporous silica was formed by hydrothermally exfoliating silicate, and the physicochemical properties and NO/Hg~(0) removal efficiency were investigated. The exfoliation induced structural reformation, resulting in a large specific surface area and the uniform dispersion of metal oxides on the surface. The transfer of valences between Cu~(2+) and Mn~(3+) in the Cu-Mn silica contributed to the single reduction peak displayed in the H_(2) temperature-programmed reduction profiles and the high Mn~(4+)/Mn and Cu~(+)/Cu ratios observed via X-ray photoelectron spectroscopy (XPS). The high oxygen lability of the Cu-Mn silica may have inhibited its ability to remove NO. By contrast, when SO_(2) was present, incorporating Ce enhanced the NO removal efficiency due to the increased number of Br?nsted acid sites. Hg~(0) removal tests indicated that adsorption was the primary removal mechanism for both the Cu-Mn and the Cu-Mn-Ce silica samples. Cu2Mn8 exhibited the highest Hg removal efficiency, suggesting that Ce’s enhancing effect on Hg~(0) adsorption was diminished when a large amount of Mn was present. Of the gaseous components, the adsorbed HCl was mainly responsible for the oxidation and subsequent adsorption of Hg~(0). Furthermore, with the addition of SO_(2), the competitive adsorption of SO_(2) and the resulting HgCl_(2) did not decrease the Cu-Mn silica’s efficiency in oxidizing Hg~(0), but the oxidized Hg was less adsorptive.