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

Category: Control Techniques and Strategy

Volume: 19 | Issue: 6 | Pages: 1421-1438
DOI: 10.4209/aaqr.2018.10.0389
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Cong-Jhen Lin1, Chuan-Lin Chang2, Chih-Fu Tseng1,3, Hong-Ping Lin 2, Hsing-Cheng Hsi 1

  • 1 Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 10617, Taiwan
  • 2 Department of Chemistry, National Cheng-Kung University, Tainan 70101, Taiwan
  • 3 Taiwan Power Research Institute, Taiwan Power Company, New Taipei City 23847, Taiwan

Highlights

  • Cu-Mn and Cu-Mn-Ce silica were prepared via silicate-exfoliation method.
  • Silicate-exfoliation caused large surface area and uniform metal oxide dispersion.
  • Ce promoted NO removal with presence of SO2 by increasing Brønsted acid sites.
  • Oxidation followed by adsorption resulted in Hg0 removal for the tested samples.
  • Adsorbed HCl was the key component responsible for Hg0 oxidation and adsorption.

Abstract

Cu-Mn and Cu-Mn-Ce oxide-incorporated mesoporous silica was formed by hydrothermally exfoliating silicate, and the physicochemical properties and NO/Hg0 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 Cu2+ and Mn3+ in the Cu-Mn silica contributed to the single reduction peak displayed in the H2 temperature-programmed reduction profiles and the high Mn4+/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 SO2 was present, incorporating Ce enhanced the NO removal efficiency due to the increased number of Brønsted acid sites. Hg0 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 Hg0 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 Hg0. Furthermore, with the addition of SO2, the competitive adsorption of SO2 and the resulting HgCl2 did not decrease the Cu-Mn silica’s efficiency in oxidizing Hg0, but the oxidized Hg was less adsorptive.

Keywords

Silicate exfoliation Coal combustion Mercury Multipollutant Metal oxide


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