Tunning active oxygen species for boosting Hg0 removal and SO2-resistance of Mn-Fe oxides supported on (NH4)2S2O8 doping activated coke
2023
Du, Xueyu | Li, Caiting | Zhang, Jie | Zhu, Youcai | Liang, Caixia | Huang, Le | Yang, Guang | Yao, Chaoliang | Ma, Ying
Active oxygen species (AOS) play an essential role in modulating the activity of activated coke (AC) based samples. In this paper, AC was endowed with abundant AOS by modifying with (NH₄)₂S₂O₈ and MnOₓ-FeOₓ for Hg⁰ removal. (NH₄)₂S₂O₈ treatment induced abundant micropores and oxygen-containing functional groups, and thus provided more anchoring sites for the dispersion of MnOₓ-FeOₓ. The synergy of MnOₓ-FeOₓ and interaction between MnOₓ-FeOₓ and NAC support contributed to a larger surface area, highly-dispersed active components, stronger reducibility, and more metal ions with high valence of MnFe/NAC. The optimal MnFe/NAC exhibited superior Hg⁰ removal efficiency above 90% at 120∼180 ℃, as well as excellent performance for simultaneous removal of Hg⁰ and NO, and 600 ppm SO₂ and 8 vol.% H₂O addition led to a slight deterioration. XPS and Hg-TPD revealed that mercury adsorbed on MnFe/NAC included phy-Hg, C=O-Hg, COO-Hg, and OL-HgO. Besides, the priority of AOS for Hg⁰ chemisorption was C=O > COO- > OL, and Hg²⁺ was also detected in the outlet. Moreover, the SO₂-poisoning effect was ascribed to the sulfation of MnOₓ and the occupation of COO- and C=O, and FeOₓ incorporation enhanced the SO₂-resistance through weakening SO₂ adsorption on C=O and COO-. The motivation of O₂ mainly contributed to the regeneration of AOS, especially OL. The excellent regeneration performance and stability further affirmed the application potential of MnFe/NAC for Hg⁰ capture from coal-fired flue gas.
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