Preparation of Cu-Mn and Cu-Mn-Ce oxide-incorporated mesoporous silica via silicate exfoliation for the removal of NO and Hg⁰

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.