Relationship between Hg0 capture performance and physicochemical properties of CeO2-CrOx mixed oxides. Issue 5 (October 2022)

• Record Type: Journal Article
• Authors: Ye, Dong; Wang, Xiaoxiang; Wang, Runxian; Hu, Yongjin; Liu, Xin; Liu, Hui; Wang, Haining
• Is Part Of: Journal of environmental chemical engineering. Volume 10:Issue 5(2022)
• Publication Date: 2022-10
• Subjects: CeO2-CrOx -- Hg0 removal -- Acidity -- Oxidative ability -- Mechanism; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2022.108252
• Languages: English
• ISSNs: 2213-2929

Abstract

Abstract: To effectively reduce the emission of Hg 0, developing an adsorbent with a superior Hg 0 removal performance constituted an important step. As a typical rare earth metal oxide, CeO2 was always used for Hg 0 capture because of its tunable physicochemical properties. However, the weak acidity and the intermediate oxidative ability restrained its effective removal of Hg 0, especially from the flue gas with a high Hg 0 content. Thanks to the superior acidity and oxidability, CrO x addition could ensure the sufficient physisorption of Hg 0 and accelerate its oxidation to HgO. Thus in this study, a serial CeO2 -CrO x mixed oxides were prepared. The sample with Ce/Cr molar ratio of 3/1 exhibited the best performance; ca . 90 % Hg 0 removal efficiency could be reached at 150 °C. Compared with virgin CeO2 and CrO x, the combination of these two metal oxides brought out a larger specific surface area, which would provide an increased number of active sites for Hg 0 removal. Meanwhile, the presence of plentiful acid sites and reactive oxygen species favored the physisorption and oxidation of Hg 0, hence contributing to a relatively high Hg 0 removal efficiency of CeO2 -CrO x mixed oxides. During the Hg 0 adsorption cycles, Mars-Maessen route dominated; Cr 6+ played the role of an active site to oxidize Hg 0, while Ce 4+ acted as a promoter-like site to boost the regeneration of Cr 6+ . Finally, CeO2 -CrO x mixed oxide exhibited a satisfactory recyclability and a relatively weak gas component adaptability, suggesting that further modification should be conducted to improve the practicality of CeO2 -CrO x mixed oxide. Highlights: The combination of CrO x and CeO2 elevates the Hg 0 removal efficiency. Adsorbent physicochemical properties mainly determine its Hg 0 capture capability. Mars-Masessen mechanism explains the Hg 0 capture process over CeO2 -CrO x surface. Cr 6+ is responsible for oxidizing Hg 0 with Ce 4+ facilitating the regeneration of Cr 6+ .